Light Metals. Vol. 7, No. 80

LIGHT ALLOY PISTON FORGINGS supplied t o t he

A I R C R A F T I N D U S T R Y during 1 9 4 3

by fU-CH DUTY ALLOYS LTD

I ® » ™ ® ® ® ! " ' " " ' _ ' " • " r r s s f S i s s g t t i 'H n B i

B R B B f l f l f l f l B R B R E I

§^£gg|§§g2J|!

SSb cB B B B B B B B B !

I ll g i g g S i !

I B B B B B B B f l P

E i l i f e s .

p b b r b i

m im iM IBBBBBBBBBBBI

i p p

g l S i i f l

_{v '}

Advts. LICH T METALS September, 1944

D E P E N D A B I L I T Y ,

REFINED ALUMINIUM ALLOY INGOT IS OUR .ONE JOB AND WE DO IT AT THE HIGHEST LEVEL OF EXCELLENCE

KNOWN TO SCIENCE

LIGHT ALLOY P R O D U C T S C & MINWORTH. B I R M IN G H A M

September, 1 944 LIC H T M ETALS Advts. i

ILFORD PLATES

for PHOTOMICROGRAPHY

I L F O R D L IM IT E D m an u fa ctu re a w ide range o f p lates and films w hich adequately covers every requirem ent o f the m etallurgist w hether for la b o rato ry research o r re c o rd p u r­

poses. E xperience has p roved th a t fo r the p h o to m icro g rap h y o f polished specim ens there is no better plate th an the Ilford C hrom atic for general use w here achrom atic lenses are used in co n junction w ith deep yellow o r green filters.

T he Ilford boo k let “ P h o to g ra p h y as an aid to Scientific W o rk ” provides the research w o rk er w ith a concise guide to the selection o f p h o to g rap h ic m aterials for every scientific p u rp o se. A copy should be in every research lab o rato ry . ILFO RD

P ro cess Plate H .& D . 25 For all cases where high resolution is necessary.

ILFO RD

C h ro m a tic Plate H. & D. 135. For polished steel sections, in conjunction with a green filter.

ILFORD

R ap id Process Pan­

c h ro m a tic Plate H. & D. 100. For speci­

mens showing oxide or sulphur films but fre­

quently used for all specimens.

ILFO RD

S.R. P a n ch ro m a tic P late

H. & D. 700. A faster plate.

ILFO RD

H y p e rse n sitiv e P a n ch ro m a tic P late

H. & D. 3,500. For conditions of low in­

tensity lighting, such as work with polarised light at high magnifica­

tions.

M ild steel sprayed on m ild steel base by w ire pisto process

B a s e M e t a l — f e r r i t e ( w h i t e ) , p e a r l i t e ( h a l f t o n e ) S p r a y e d M e t a l — 1 s t p h a s e ( w h i t e ) , 2 n d p h a s e ( h a l f t o n e ) , p o r e s ( b la c k (B y courtesy o f Messrs. Metallisation Ltd., Staffordshire Education Committei

and H . A . M acColl, B .Sc.)

E T C H E D —Picric Acid M A G N IF IC A T IO N — X 150 O BJECTIV E— 16 m m . achrom at

N .A . O. 28

IL L U M IN A T IO N — G lass slip ver­

tical illum ination

Technical Details

EY EPIECE— X 6 com pensating L IG H T SO U R CE— 100 c.p. P o in t

olite D.C.

FILTE R — Ilford M icro 3 (green' PLA TE— Ilford C hrom atic E X PO S U R E— 50 secs.

I L F O R D L I M I T E D • I L F O R D • L O N D O N

¡¡ Advts. LIC H T M ETALS September, 1944

L

S l Q CK . B IN L I G H T I N G

T h e im p o r ta n c e o f being able to find w h a t y o u w a n t w h en y o u w a n t it m e an s th a t y o u need suitable lighting to see w h ere it is.

B e n j a m i n S t o c k B i n L ig h tin g U n its h av e been specially designed fo r this p u rp o s e , they direct the light in to the rack s w h ere th e g o o d s a re a n d shield th e eyes o f the sto rek eep ers fro m glare. Y o u r local B enjam in E n g in e e r c an give y o u details.

B E N ⁷ A M J N

F L U O R E S C E N T ________________________ I___

I I I

D I S C H A R G E —

Ü J L

F I L A M E N T

I I I I | | | | 1

The Benjamin Electric Ltd., Brantwood W orks, Tottenham, London, N .I7

T e l e g r a m s : •* B e n ja le c t. S o u th t o t . L o n d o n ” T e le p h o n e : T o tte n h a m 5252 (5 lin es)

J_______________I________ LJ______________I________ U____________ 1_________L

^«93

September, 1944 LIC H T M ETALS Advts. in

POST-DATED INVITATION \

TO BUSY MANUFACTURERS AND DESIGNERS

W hen you have a moment to spare you may wish to consider the post-war possibilities

of Aluminium in relation to your business.

The potential uses of Aluminium alloys have increased enormously during the last few years and very few industries will remain unaffected by this development after the war.

W rite to Northern Aluminium and we will tell you if and how Aluminium can play an

important part in your particular post-war business.

We can give you t A b I b about ALUMINIUM NORTHERN ALUMINIUM COMPANY LTD., «mm».««

Makers of ^NORAL Products

iv Advts. LIGHT METALS September, 1 944

A ye, i t ’s a g ra n d song b u t it d o esn a’ do for m in d s to go ro a m in g in tb e gloam ing o f in c o rre c tly lig h te d w o rk sh o p s a n d facto ries. T h a t’s b a d for p ro d u c tio n . In c o rre c t lig h tin g is a b a r to c o n c e n tra tio n a n d im poses a s tra in u p o n th e w o rk e rs’ h e a lth , w hile c o rrec t lig h tin g increases p ro d u c tio n . I f y o u r in s ta lla tio n needs b e tte r p la n n in g or changes are re q u ire d to ta k e care o f new processes, or ex ten sio n s are necessary — co n su lt th e G .E.C . T a k e a d v a n ta g e o f th e know ledge G .E.C . lig h tin g sp ecialists h a v e gained in help in g w a r-tim e facto ries to w a rd s full p ro d u ctio n .

F O R A N Y S T A N D A R D O F

¡ ¡ . L U M I N A T I O N

Adyt.

o f The G e n e ra l E le c t ric Co., Ltd., M a g n e t H ou se , K in g sw a y ,

W.C.2.

^I.E.I6

September, 1944 LIGHT M ETALS Advts. V

B r o n z e o f c e l l u l a r s t r u c t u r e i m p r e g n a t e d w i t h l u b r i c a t i n g oi l

“ O ilite”

reduces bear­

in g failures to a m inim um w herever it is applied , to suitable com ­ ponents. T he lubricant content is ample to cope w ith variations in speed and load o v er a considerable range, and will d o this continuously d u rin g the life o f the com ponent, w hilst, w here necessary, addi­

tional lubrication can be readily em bodied in the design w ith o u t difficulty. T he accuracy o f finished dim ensions and limits is equal to that o f the highest grade m achined bearings, thus m aking fo r ease o f assembly and fitting. As an alternative to force fitting, “ O ilite” can, if desired, be em bodied in L ig h t M etal D ie C astings d u rin g casting, thus reducing the m anufacturing oper­

ations o f the com ponents, although

O il m ust be im pregnated later.

vi Advts LICH T METALS September, 1944

VICTOR £ u fze á M ¿< x, X-RAY FILM PROCESSING CHEMICALS

S U P E R M I X P R IC E S

D e v elo p er :

t o make 1 gall. 6/6

„ 2 „ M / -

. . 5 „ 2 7 / - F i x e r :

to make 1 gall. 5/6

„

2

„

91-

„ 5 „ 2 3 /-

c t i

0 4

e c u H f 0 4 t h a t - You simply p o u r th ese liquid co ncen trates into your tanks and add w a t e r ... no tim e lost in dissolving p ow d er s o r adjusting solution tem p e ratu res. They will reveal in ev ery film all th e diagn ostic qualities which your e x p o s u r e makes possible, in co ntrast, density and detail.

a t t d a d e c a n o n u c o l a d t h u d - W ith th ese longer-lasting Su p e r m ix solu tion s you can process up to 7 5 % m o r e films than with conventional processing chemicals. Unusual speed o f deve loping (3 minutes at 6 8 ° F.) and fixing (less than 1 minute) will e x p e d ite y o u r dark ro o m w o r k ; or, by developing 5 t o 6 minutes you can r educe x-ray e x p o s u r e 2 0 % t o 2 5 % t o econom ise in tu b e life. LONG-LIFE S P E E D C O N V E N I E N C E are th e hall­

mar ks o f Victor SUPERMIX.

V ICTO R X -R A Y CORPORATION Ltd.

I5 -I9 C a v e n d i s h P l a c e , L o n d o n ,

W.i

L A N g h a m 4074

BIRMINGHAM BRISTOL GLASGOW MANCHESTER DUBLIN

BELFAST EXETER LEEDS SHEFFIELD NOTTINGHAM LIVERPOOL

The Birmingham Aluminium Cast

Birmid Works' - • Smethwick -40 (1903) Co. Ltd.

Birmingham

Se p te m b e r , 1 9 4 4 L IG H T M E T A L S A d v t s . vii

■ :

'/■ \V

viil Advts. LIG H T METALS September, 1 944

T H E

R E D U X

P R O C E S S

JL H E R e d u x p ro c e ss p ro v id e s, th ro u g h th e u se o f sy n th e tic re s in a d h e siv e s, a m e th o d o f b o n d in g lig h t a llo y s a n d ste e l w ith a s tre n g th ex c ee d in g t h a t o f r iv e tin g —'an d a lso o f m ak in g s tro n g jo in ts b e tw e e n m e ta l a n d w o o d . A f t e r p ro lo n g e d te s ts R e d u x h a s b ee n a d o p te d b y a n u m b e r o f firm s en g a g ed in e s s e n tia l w o r k a n d th e re is e v e ry re a s o n to b e lie v e t h a t w h e n th e gu n s c e a s e firing, th e R e d u x p ro c e s s w ill find m a n y n e w a p p lic a tio n s . R e a lis in g th e im m en se p o s s ib ilitie s o f th e R e d u x p ro c e ss in th e f a b r ic a tio n o f a r tic le s m a d e fro m lig h t a llo y s A e ro R e s e a r c h L td . w ill be h a p p y to give full in fo rm a tio n o f th e p ro c e s s a n d its s u ita b ility fo r a n y p a r ti c u la r ta s k .

A E R O R E S E A R C H L I M I T E D

D U XF O R D CAMBRIDGE

J OHN M E E R L O O & S O N S

7 4 . L O N D O N RD. KIN G S TO N -O N -T H AM ES

B.K.L. ALLOYS LTD.

‘ F A C T O R Y C EN TR E,

KINGS NORTON, B IR M IN G H A M

P h o n e :

K IN G S N O ltT O N 1IG2/5 G ra in s : A L IN G O T S , B IK M IN G H A M

a l u m in iu m i n g o t s

A N D C A S T A L L O Y S IN A C -

feA'; TESTAL ⁴

I s p e c ific a tio n K-

I D .T .D . 4 2 4 ' r i . ,, n o c c o rd a n c c

for »HIGH GRA

dk

■■ u'' J ESTAL 'o

I Ä , Ä C<1

D .T .D . 4 2 4 w h e re r e q u ir e d is a ls o s u p p lie d S O D I U M M O D I F I E D o r w ith th e a d d itio n

o f T I T A N I U M

September, 1 944 LIC H T M ETALS Advts. Ix

,o»rłA'’

X

Advts. LIC H T M ETALS - September, 1944

I N A M O DERN P LA N T

; y< ;

⁸

® S SSJS £ ~7- •"

U RG EN T W O R K H A NDLED

I

M M E D

I

A T E L Y R A D C L I F F E 2 6 3 7 -

CREO SO TE- PITCH FIRING

A num be r of firms adop ting this fuel have encou nte red new Refractory Problems caused by co rrosion and Vitrification Spalling.

If a suitable design of burner is used, the trouble can usually be overcome by using a High Alumina Firebrick such as NETTLE (42/44% Alumina)—a point proved by the practical experience of several customers.

An additional protection to the brickwork by washcoating with Maksiccar II. or Stein Sillimanite Cement will often be found economic. Further information will be gladly supplied on request.

JOHN G.STEIN&C°LTD

S C O T L A N D

DAY &

NIGHT

S E R V I C E

AVAILABLE

For anodistrtg of A lum inium i <-< ¡ÜJ '■

and its alloys; C b ro m atin g of

■ ■

M agnesium :' Zinc & C adm ium P lating: El-Tin, etc., to A.I.D.

specifications. W e a re specially

? ■ ■: 5 ‘ . , ‘ equipped w ith larg e u p t o d a te

. o -

p la n t capable of handling bulk

: . . .• - . • . .

w ork a t speed. Also HEAVY , NICKEL an d H a rd C h ro m e

' ' a v a ila b le a t s h o r t n o tic e .

d m 1030

w a n t '

Yoü. r ^ -

or nL

• O w in g to th e restr icte d use o f Aluminium, Dies for producing Aluminium C astin g s can be modified for Brass Product io n.

• Let us, as the Pioneers o f Brass G ravity Die C astin g , help you in y o u r Technical P roble m s.

• O u r Highly Skilled Technical Staff, M odern Foundries and many y e a r s ’ E xperience a r e at Y o u r Se rvice.

N O N - F E R R O U S

D IE C A S T I N G C O . L T D . N o rth C irc u la r Road, Cricklew ood, L O N D O N , N .W . Telephone: GLAdstone 6377

TELEPHONE

September, 1944 LIC H T M ETALS Advts. x¡

ALUMINIUM BRONZE

IN P R O D U C T IO N W IT H

( KENTÂ ¹ L ⁰ ÏS LT ¹ a

S P E C IA L IS T S IN N O N -F E R R O U S C A S T IN G S HEAD O FFICES: COM M ERCIAL ROAD. STROOD

NON-FERROUS CASTING TECHNIQUE

Control . . . Consistency.

Confidence .

The care which is taken aiul the

skill which is exercised in every

detail of modern non-ferrous

foundry work is best

appreciated by those

wrho lest the finished

product.

x¡¡ Advts. LIGHT M ETALS September, 1944

["ADMINISTRATIVE MACHINE TOOLS"

A ny curing, d ry in g or baking process w hich c an be safely c arried o u t in a sh o rt tim e a t a h ig h tem p era tu re, instead of a long tim e a t a low tem p eratu re, is specially suited to the use o f infra-red ra d ia n t heat.

P a in t an d ink drying, biscuit baking, fur d ry in g a n d several o th er specialised p ro ­ cesses dem an d in g high rates o f h e a t transfer h ave for years b een c arried o u t m ore cheaply, quickly an d efficiently by ra d ia tio n (or infra-red) from a gas source.

M a n y existing gas-fired appliances m ay b e reg ard ed as o f the in fra-re d type, and existing conveyor ovens c an in some cases be eq u ip p ed w ith in fra-red units, b u t, w h ere new p lan t is to be installed, it is well to b e a r in m in d th e advantages o f the gas-fired tunnel :—

1. Simple, robust, inexpensive and compact, giving long life with minimum maintenance.

2

. Easily constructed in different sizes and shapes, without the need for complicated auxiliaiy apparatus.

3

. Very wide range of flux density, which can be varied by turning the tap.

4

. Even distribution of radiation.

5

. No material difference in drying time due to colour.

6

. Low capital, fuel and maintenance costs.

Further information is con­

tained in a Paper, entitled

* Radiant Heating for Indus­

trial Purposesfree on request.

SEND FOR A COPY OF THIS BROCHURE which deals comprehen­

sively with the subject.

B R IT IS H C O M M E R C IA L GAS A SSO C IA TIO N I GROSV F.N O R P L A C E , L O N D O N , S . W I .

T h e r e seem s little d o u b t a b o u t th a t, as o n e loo k s a ro u n d . B u t as one loo k s a ro u n d , one realises, to o , th at p ro d u c tio n w as o f ten a good deal b e tte r th an p ro d u c tio n m eth o d s.

‘So w h a t? ’ y o u say, ‘W e w ere a sk e d fo r o u tp u t first, seco n d an d l a s t! ’ A g reed . A n d th e re su lts are ex cellen t

— b u t o n ly in th e special c ircu m stan ces sin ce D u n k irk .

S o u n d e r m eth o d s a re n eed e d to w e a th e r th e im m in en t w ith d raw al of m o re m en fro m in d u s try . . . and to org an ise an efficient s e t-u p to g reet th e peace.

T h ro u g h th ese fo u r y e ars K ard ex h a s b e e n s o l v i n g p r o b l e m s and.

g a th e rin g new e x p erien c e w h ich can n o w b e a p p lie d to to d ay ’s special headaches.

i t PRODUCTION CONTROL, by A. R. Jackson.

The above booklet presents an outline of produc­

tion control problems and practical solutions.

Sent on application for If- post free to Dept. Z.9 Kardex systems are available only to essential industries.

K A R D E X V I S I B L E C O N T R O L S Y S T E M S 1 - 1 9 . NE W O X F O R D S T R E E T . L O N D O N . W. C . l

CHAntery iBSS

September, 1944 LIC H T M ETALS Advts. xiii

• Sola Producer» and Pro prit to n o f tho T r td t M u k "Elektron” : MAGNESIUM ELEKTRON LIMITEO. Abbey Houie. London. N .W .I • Ueenied Manufactura«*

Castings & forgintt: STERLING METALS LIMITED. NoetHey Road. Foleihill. Coventry • CaUirtix: THE BIRMINGHAM ALUMINIU M CASTING (19031 COMPANY LIMITED. Birmld Work». Smethwick. Birmingham • J. STONE * COMPANY LIMITED. Deptford. London. S E M • Sheet. Extrusions, f or tin ts 4 Tubes • IAMES BOOTH ft CO. (1915) LIMITED. A rjyle Street Work». Nechell». Birmingham. .7 • Sheet. Extrusms. Etc.; BIRMETALS LIMJTED Woodgatc. Qulnton. Birmingham

• Suppliers o f M ignnlum and "E la k tro n " Matal fo r the British Empire : F. A. H UGH ES ft CO. UMITED. Abbey Home. Baker Street. London. N W I

^ ) r e p s l a n t p e ^ Q e r q i n q s

i n ^ l e L l r o n m a q n e s i u m a l l e y s

couthitjuti&u to th e te/UvHicjue o j

I I n s u l a t i o n ! I

K I M O L O

KIMOLO Insulating Bricks, now in plentiful supply, pro­

vide the up-to-date answer to heat-insulation problems.

Manufactured in Kent from local materials they have

p ro v e d ,

both in official tests and in wide application, to equal or better the performance of insulating bricks dependent on imported materials. Engineers, metallurgists, chemists, and all in charge of fuel-burning plant are cordially invited to apply

at once for full technical data.

CL O tu itn fd t o f QhvfccZ'b k fjfvoductCcm

I ST A N D A R D G R A D E I IN SU LA T IN G BR IC K

Sole KIMOLO MANUFACTURERS LTD.

Distributors: CELLACTITE &BR1T1SH URALITE LTD.

Terminal House, 52, Grosvenor Gardens, London, S.W.l.

Telephone: SLOane 5127 (4 lines).

Telegrams: Cellactlte-Sowest-London.

FO R A L U M I N I U M A N D A L L O Y B I L L E T S O R S L A B S

g i b b o n s

R E - H E A T I N G F U R N A C E . S

M-W .71)

xiv A d v t s. LI G H T M E T A L S

A L U M I N I U M & A L L O Y R E - H E A T I N G F U R N A C E S

T h e F u rn a c e illu s tra te d is h e a le d b y a series o f G a s F ire d R a d ia n ts . T he w a s te g a s e s from th e ra d ia n ts c a n b e d i­

v e rte d e ith e r into th e h e a tin g c h a m b e r in co n ta c t w ith th e p r o ­ du ct, o r ca n b e e v a c u ­ a t e d d i r e c t t o t h e c h im n e y . The te m p e r­

a tu re is c o n tro lle d b y M u lti- Z o n e A u to m a tic P y r o m e tr ic E a u ip m e n t, w h ic h to g e th e r w ith th e G ib b o n s ' Sy stem o f H e a tin g a n d Fan Re-circula1 ion en s u re s c l o s e t e m p e r a t u r e co n tro l.

Gibbons B ros. L td ., D i b d a l e W o r k s , D udley. P hone 3141

September, 1 944

T A S /C L B .3 0 5

September, 1944 LIC H T M ETALS Advts. XV

5 . W O L F E- CO. LTD . P I O N E E R W O R K S . H A N G E R L A N E . L O N O O N . W.5. P E R iv a l e S 6 3 I - 3

Wolf

O k c /ù ÿ ie n < H i//e Q ^ iu c Ä tn e d ¿ n Q ^ h c /u ó é r y

1444

xvi Advts. LIC H T METALS September, 1944

E L E C T R I C F U R N A C E S

Advt. of The General Electric Co. Ltd., Magnet House, Kingsway, London, W.C.2.

L e t t h e m a l l k a n q

t o g e t h e r /

Why let your documents play hide and seek in leaning, sagging folders when they can be filed quickly and found instantly in Shannograph full-vision flat top folders, which hang on a metal frame and never slip or hide. An infinite variety of indexing is possible on the flat top, with fixed or movable signals on the Visible Edge for progress, production control, etc. Frames fit any standard filing cabinet or deep desk drawer.

Send Id. stamp for leaflet.

T H E S H A N N O N LIM ITED

IM PERIAL HOUSE (Dept. E.2), 15-19 KINGSWAY, LONDON, W.C.2

And at Birmingham, Bristol, Liverpool. Manchester, Newcastle, Glasgow (Agent)

ON ITS METTLE

Th ro u g h o u t the national effort runs the need for m etal— m ore m etal, b e tte r m etal, tougher m eta l—

strengthened and vitalised by heat tre a tm e n t.

G .E .C . E le c tric Furnaces provide an answ er to every

problem of hardening, tem pering, annealing, nitriding,

etc., by w hich the in heren t strength and stam ina of

m etal a re developed to m eet e ver m o re exacting uses.

September, 1944 LIG H T M ETALS Advts. Xvü

M E T A L A S T I K B U S H E S

4BI

with an annular rubber cushion [rubber-to-metal w eld ]

These bushes take the place o f a design employing forgings extensively machined, but do the work

just as well and save man - and - machine hours . . . and money.

The metal housing Is p r e s s e d - y e t rigid;

a good example of the fact that Metalastik engineering is not confuted to rubber only, but is focused upon metal and rubber united by the Metalastik rubber- to-metal-weld In o r d er to produce an outstanding result.The bush at the bottom is of a different type; in som e applications a flanged construction simplifies the design

o f the equipmen t to which the bush is fitted.

These bushes are used for many purposes, f o r v i b r a t i o n i n s u l a t i o n , a l s o f o r

mountings for oscillating parts.

A rem inder: with our com plete vibration research equipm entwe can analyse vibrations how ever com plex and from whatever cause, and so far

have never failed to provide a rubberm ounting w hich reduces them to tolerable limits.

M etalastik Ltd. Leicester

StlR 111

i l l

C RYO LITE was the crystal key unlocking the d o o r to th e indus-

’ trial production of aluminium.

The tw o pioneers, Hall in America and H eroult in France, hit upon the , use of this flux in th e y ear 1886. .]

CRYOLITE is a double fluoride of aluminium and so dium which oc cu rs in N atu re, but is now produced syn- .vJjjfl thetically. T o split alumina into oxygen B H R r ' and aluminium nee ds a heavy electric

curre nt, and the alumina m u st be molten.

Alumina melts at o v e r 200 0 °C ., but a 10 per cent, m ix tu r e o f alumina In cryolite melts at under IOOO°C., and the passage of an electric cu r re n t th rough such a m ix tu r e th r o w s o u t the oxygen, leaving th e molten aluminium at the b o ttom o f th e bath. W ith detail refinements the Hall/H eroult disco very o f the value of cry.olite is still the basis o f aluminium production to-day.

E CRYSTAL KEY

T e m p o r a r y H e a d O f fic e :

SALISBURY HOUSE, LONDON WALL, LONDON, E.C.2

T e le p h o n e : C L E rk c n w e ll 34*4 T e le g ra m * * C r y o lite , A v e , L o n d o n

V O L. V II. N o. 80. S E P T E M B E R , 1944.

Proprietors:

T E M P L E P R E S S L T D .

Editor:

E . J . G R O O M , M .In s t.M E T .

Managing Director :

R O L A N D E . D A N G E R F IE L D

D e a l i n g A u th oritatively w ith the P rod u ction , U se s

a n d P oten tialities o f L ig h t M e ta ls a n d

their A lloys

Offices:

B O W L IN G G R E E N L A N E , L O N D O N , E . C . r

E D IT O R IA L O P IN IO N

D o n ’t Shoot ! Call The D octor !

N LY w ith the greatest reticence do we ad d o u r voice to th a t growing volum e of opinion w hich says " W e ll, th a n k goodness th e w ar is nearly o v e r." We certainly believe this statem ent to be true, but, a t the sam e tim e, feel a little an x iety over ou r readiness to m eet the situation w hich will arise when peace breaks out.

F o r a long tim e now the world h as been divided into two cam ps—post-w ar planners, on the one side, an d those who say " L e t ’s w ait until th e show is o v e r,”

on the other; it m ust be adm itted th a t, lately, frequent desertions have occurred from the la tte r group.

T he more cautious of those who realized early th e need for in itiating schemes of post-w ar reconstruction were, from the beginning, only too ready to ad m it th a t th e final shaping of a n y p la n s would depend upon th e result of innum erable political, econom ic, social an d o ther factors w hich would em erge when hostilities ceased. O thers, less restrained, were deceived by a m irage and saw the Golden Age alread y loom ing on the horizon. E ven now, a t this stage, it is still too early to m ake h ard an d fast decisions. O nly one essential can be postulated. P lan s for the post-w ar period th e re m ust be, an d th e y m u st exist in a presentable, w orkable form w ithin the space of the next 12 m onths.

I t is inevitable th a t m any of the schemes ab o u t w hich we hav e h eard so m uch will prove im practicable, b u t it is v ital th a t all internecine quarrels be e lim in a te d : times are too critical to mock the unsuccessful enthusiast w ith a cry " P hysician heal thyself ra th e r th e doctor m ust be called in, schem es recast, plans readjusted and p urged to m eet conditions as they w ill he, an d not as it w as hoped they m ight have been.

T he difficulties w hich face us all are alarm ing in th eir n um ber an d , im m ensity.

A rgum ent, friendly or acrim onious, is waged over details, a n d th e onlooker m ay

be tem pted all too readily to draw false conclusions from the p icture as he sees

it presented in the p o pular Press, or hears it stated from th e public platform .

W e m ight cite, as an exam ple, the som ew hat undignified bickering w hich has

broken out over world m onetary plans for th e New Age. P artisa n s have arran g ed

412 LICHT METALS September, 1944 them selves round this or th a t centre of dissent, an d quite a false appearance of incoherence has been created. Once again we hear w hispered the possible out­

b rea k of a " w ar of the m etals.” (T he title of an alarm ing report presented by

” F o rtu n e ” in 1939.)

R aw -m aterial com petition we m ust expect, for only by this m eans can real pro ­ gress be assured; b u t we believe th a t this will be friendly com petition based on th e respective m erits of the m aterials concerned, and not th e sinister political gam bling w hich certain nervous subjects have been led to fear. F o r, in the long run-, th e ultim ate destiny of all the new m aterials— m etals an d non-m etals— w hich hav e come into cu rren t use to a greater or lesser ex ten t during the p a s t 25 years will be this: the bag will be shaken down a n d the contents sieved an d sorted, the final position being such th a t each will stan d com plem entary to the other. Such has been- the course of evolution from th e Stone Age upw ards. If th e Eskim o still uses bone needles for sewing his skins, it is only because, in the Arctic, th e " little shop round the corner ” is a long w ay off and m ay n o t sell steel ones, anyw ay.

T he force of this elem entary argum ent seems to hav e escaped m any, some of whom would have us believe th a t the years to come will see the daw n of an ” All- P lastic ” Age; others, well m eaning b u t equally m isguided, talk in term s of an " All- A lum inium " Age. W hilst from the view point of purely personal interest the con­

sum m ation of this la tte r dream would be desirable, we know th a t it cannot be so.

E ach group of interests will, q uite rightly, strive to p ush to the forefront its own p articu la r creation, an d , by publicity of all types, m ake certain th a t the v a st con­

sum er field is fully appreciative of its m erits; b u t balance is required an d p ast experience teaches us th a t to some projects we m ust regretfully say " n o ,” even though, in so doing, we lose th e opp o rtu n ity of selling a few more th ousand tons of light m etal or a few more square miles of polyvinyl-chloride sheet.

P erhaps, because of this, it is vital, in the form ulation of o u r own p articu la r post-w ar plans, th a t we are fully aw are from the beginning of ou r precise stand.

T his can be achieved only b y tak in g full ad v a n ta g e of every possible opportunity for corporate and individual research. P ositive d ata we know we m ust have to m eet the flood of inquiries which will come in; negative d ata, even if we do not b ro ad cast it, should be filed to p rev e n t others m aking m istakes w hich we ourselves

m ust n o t com m it again.

A lum inium an d m agnesium have won th e ir places in the engineering w orld not solely on account of sales ta lk , b ut, fundam entally, because they have fulfilled physical needs. L ight-m etal forgings and castings, rivals though they m ay have appeared in the past, have each attain ed th eir own level in response to definite m echanical and economic dem ands.

Contents

Page Page

SPECIAL ARTICLES Aluminium for Be ginn ers . . 459

Chemical Protection of Mag­

nesium A ll o y s ... 413 R E G U LA R FEATURES

Machining of Light Alloys with Editorial Opinion . . . . 411 Diamond To ols . . . . 430

Light Alloys in Metal Rectifiers N ew s — Genera l, T e c h n i c a l , and Photocells . . . . 4 3 7 C o m m e r c i a l ...423

THE FACT that goods made of raw materials in short supply because of u'ar conditions are advertised in this journal should not be taken as an indication that they are necessarily available for export.

SAVE PAPER—More than ever is paper waste required for our war industries. Waste paper makes

munitions in a hundred forms—from shell cases to aeroplane parts.

September, 1 944 LIG H T M ETALS 413

Chemical Protection o f M A G N E SIU M ALLOYS

Summary, with Commentary, o f Some Recent Patents Embodying Comprehensive Detail Regarding Fundamental Theory o f Chromate Processes and Their Commercial

Application

O

F th e n u m e r o u s c h e m ic a l m e th o d s d e v e lo p e d fo r th e p ro te c tio n o f m a g n e s iu m a n d its a llo y s , th o s e u s in g c h r o m a te s o lu tio n s h a v e p ro v e d o u t s t a n d in g ly su c c e ss fu l. A ra n g e of s u c h tr e a t m e n t s e x is ts , v a r y i n g w ith r e s p e c t to s o lu tio n c o m p o s itio n a n d tim e a n d t e m p e r a tu r e o f t r e a t m e n t . T h e y a re e m p lo y e d fo r g iv in g p r o te c tio n to w r o u g h t a llo y s in th e fo rm of s h e e t, ro d , e tc ., a s w ell a s to c a s tin g s d u r in g s to ra g e , d u r in g fa b r ic a tio n p ro c e sse s a n d fo r p r o te c tio n u n d e r s e rv ic e c o n d itio n s . I n a d d itio n t h e y a re u sed a s p r e p a r a t o r y tr e a t m e n t s p r io r t o p a i n t i n g o r e n a m e llin g . A ll th e s e p ro c e sse s n e e d c a re fu l c o n tr o l in o p e r a tio n in o r d e r t h a t t h e b e s t re s u lts m a y b e o b ta in e d . S u c h c o n tro l is a p p lie d b y p e rio d ic a n a l y s is o f s o lu tio n s , b y p H m e a s u re m e n ts a n d b y s t i p u l a t i n g th e a m o u n t o f w o rk t h a t c a n b e t r e a t e d b e fo re fresh a d d i t i o n s b e c o m e n e c e s s a ry . H o w e v e r, th e fu n c tio n o f e a c h b a t h in g r e d ie n t sp ecified , a n d v a r ia tio n in e ffe c tiv e n e s s w ith th e u se o f a s o lu tio n o v e r a p e rio d o f tim e a r e n o t a lw a y s fu lly a p p r e c i a te d .

Fig. 1.—Curve show ing relationship betw een sulphate content of treatm ent bath and the

corrosion rate of treated alloy.

Fig. 2.—Curve showing relationship between pH of bath and corrosion

rate of treated alloy.

T h e M a g n e s iu m M e ta l C o rp n ., L t d ., h a s r e c e n t ly c o m p le te d B r itis h p a t e n t s 558983

(

19

.

14

),

a n d 559071

(

1944

).

w h ic h a re , in e ffe c t, tr e a tis e s o n t h e s u b je c t o f c h r o m a te p ro te c tio n , g iv in g m u c h d e ta il o n th e in flu e n c e o f th e c h r o m a te its e lf, m e ta llic s a l t a n d o t h e r a d d itio n s , p H c o n tro l a n d t h e in flu e n c e o f th e fa c to rs o f tim e a n d te m p e r a tu r e .

B.P. 558983

re la te s to t h e s u rfa c e tr e a t m e n t o f m a g n e s iu m -b a s e a llo y s , e sp e c ia lly th o s e re fe rre d to in D .T .D . sp e c ific a tio n s , b u t a lso o th e r s o u ts id e th i s ra n g e . T h e fu n c tio n s of th e t r e a t m e n t a r e , first, to g iv e p r o te c tio n t o th e m e ta l d u r i n g t r a n s i t a n d s to r a g e , w h e t h e r in t h e fo rm o f c a s tin g s , s h e e t, e x tru s io n s , o r f o rg in g s; s e c o n d ly , to s e rv e a s a b a s e fo r p a in t, e tc ., g iv in g s u p e r io r a d h e s io n a n d e n h a n c e d p ro te c tiv e p o w e rs to t h e a p p lie d film .

T h e use o f d ic h r o m a te s a n d o f c h r o m a t e s to i n h i b i t th e c o rro s io n o f m a g n e s iu m h a s lo n g b e en k n o w n . T h e p ro te c tio n a ffo rd e d is d u e to th e f o r m a tio n o f a p r o te c tiv e film b y re a c tio n on t h e s u rfa c e o f t h e m e ta l. S im p le d ic h r o m a t e s o lu tio n s d o n o t h a v e m u c h p r a c tic a l v a lu e b e c a u s e r a t e a n d e x t e n t o f film f o r m a tio n a re s e v e re ly lim ite d . C o n s e q u e n tly , a n u m b e r o f p ro c e ss e s h a v e b e e n d e v is e d (m a n y o f th e m p a t e n t e d ) , w h e re b y th e film c a n b e b u i l t u p a n d g iv e n t h e n e c e s s a ry q u a litie s to y ie ld th e p r o te c tiv e p o w e rs d e s ire d .

A t r e a t m e n t t h a t c o m b in e s a ll t h e d e s ire d a t t r i b u t e s w o u ld e m b ra c e th e fo llo w in g :—

(a ) M in im u m d im e n s io n a l c h a n g e s h o u ld o c c u r so t h a t a r tic le s m a c h in e d to clo se to le ra n c e s c a n b e t r e a t e d w i t h o u t h a rm .

(b ) R a w m a te ria ls e m p lo y e d m u s t b e in e x p e n s iv e a n d , d u e p r e c a u t io n s b e in g ta k e n , r e la tiv e ly h a rm le s s to o p e ra to rs . R a t e o f c o n s u m p tio n m u s t b e re a s o n a b ly lo w , a n d b a t h s t a b i l i t y s h o u ld b e h ig h .

414 LIGHT M ETALS September, 1944

(c) T im e o f t r e a t m e n t m u s t b e a s s h o r t

a s p o s sib le , fo r e x a m p le , p re f e r a b ly n o t m o re t h a n a few m in u te s .

(d ) T r e a t m e n t s h o u ld , id e a lly , b e c a p a b le o f o p e ra tio n a t o r d in a r y s h o p t e m p e r a tu r e .

(e) T h e p ro c e ss m u s t b e e a s y to o p e ra te m e c h a n ic a lly a n d t h e s o lu tio n s m u s t b e s ta b l e a n d re a d ily m a in ta in e d .

T h e p r e s e n t p a t e n t c la im s t o d iff e r fro m a ll t h a t h a v e h i t h e r t o a p p e a r e d , in so f a r a s it c lo s e ly fu lfils t h i s s c h e d u le . I t s u r v e y s , f u r t h e r ­ m o re , e x is tin g p a t e n t s t h a t c o v e r o n e o r m o re o f th e s e p o in ts . T h u s : B .P . 287450 d e s c rib e s t h e u se of a n a c id , s u c h a s n itr ic a c id , a d d e d to t h e s o lu tio n w ith th e o b je c t o f in c re a s in g r a te o f film fo r m a tio n . T h i s p a t e n t s t a t e s t h a t h y d r o c h lo ri c o r s u lp h u ric a c id s m u s t n o t b e u s e d , w h e re a s t h e p r e s e n t p a t e n t fin d s s u lp h u ric a c id to b e e m in e n tly s u ita b le . T h e o b je c tio n fo u n d w ith t h e n itr ic -a c id t y p e o f s o lu tio n is t h a t i t is o p e r a te d a t h ig h a c i d ity , w h ic h m a k e s i t u n p l e a s a n t in u se a n d c a u s e s m a rk e d d im e n -

Fig. 3.—Curves showing relationship betw een aluminium content of alloys treated an d pH (optimum, minimum and maximum) of chrom ate solution for

satisfactory treatment.

sio n a l lo ss in th e w o rk . A g a in , d u e to th e e x t e n t o f re a c tio n , th e s o lu tio n r a p id ly b e c o m e s e x h a u s te d .

T h e s e o b je c tio n s a re o v e rc o m e b y B .P . 305197 w h ic h o m its th e a c id a d d itio n , b u t r e q u ire s th e s o lu tio n t o b e u s e d b o ilin g ; th is is a d i s a d v a n ­ ta g e , n o t o ffse t b y a n y d e c r e a s e in tr e a t m e n t tim e , w h ic h , in a c t u a l f a c t, is s t a t e d t o b e o n e h o u r o r lo n g e r.

B .P . 331853 u s e d a h e a t e d s o lu tio n a t 95- m o d e g re e s C ., th e s o lu tio n b e in g n e u tr a l o r a c id , a n d c o n ta in in g a n a lk a li m e ta l d ic h r o m a te to g e th e r w i t h a n a lu m in iu m s a l t o r c o m p o u n d s u c h a s p o t a s h a lu m ; t h e fu n c tio n o f th is a lu m in iu m s a l t is n o t sp e c ifie d . T h e p ro c e ss re q u ir e s lo n g t r e a t m e n t tim e (1-10 h o u r s ) a n d i t e n ta ils c a r e f u l a t t e n t i o n , to e n su r e t h a t lo sses b y e v a p o r a t io n a re m a d e u p .

B .P . 353415 u ses a n a q u e o u s s o lu tio n c o n t a i n ­ in g a c h r o m a te o r d i c h r o m a te w h ic h m a y b e of a n a lk a li m e ta l, o f a n a lk a lin e e a r t h m e ta l o r

o f a m m o n ia o r o f o n e o f t h e s u b s t i t u t e d d e r i v a t i v e s o f a m m o n ia w h ic h a r e s ta b l e in h o t a q u e o u s c h r o m a te o r d ic h r o m a te s o lu tio n s . T h e s o lu tio n a lso c o n ta in s s a lt s o f o n e o r m o re o f s u c h m e ta ls o r b a se s w i t h o u t th e u se of c o m p o u n d s of m a g n e s iu m o r of a lu m in iu m o r o f s a lt s o f th e h e a v y m e ta ls . A g a in , t h e f u n c ­ tio n o f th e s a lts is n o t s t a t e d . S o d iu m s u lp h a t e is g iv e n a s a n e x a m p le . D is a d v a n ta g e s t o th is p ro c e ss a r e a s fo llo w :— T h e s p e c ific a tio n c a lls fo r p H v a lu e t o b e m a in ta in e d b e tw e e n 3 a n d 5, h e n c e f r e q u e n t s m a ll a d d itio n s o f a c id a r e re q u ire d ; i n t h e r a n g e o f p H 5 t o 7, w h e re th e s e a d d itio n s a re u n n e c e s s a ry , t h e s o lu tio n is le ss e ffe c tiv e . A g a in , i t is a h o t s o lu tio n r e q u irin g le n g th y t r e a t m e n t tim e . I n th e p r e s e n t sp e c ifi­

c a t io n , s h o r t t r e a t m e n t tim e , a n d e ase of o p e r a tio n in t h e m o s t e ffe c tiv e p H r a n g e a re s e c u re d . F o r th is p u r p o s e a s u lp h a t e c h o se n fro m t h e g r o u p c o m p ris in g th o s e of w h ic h t h e c a t io n r e m a in s s t a b l e a t t h e c o n c e n tr a tio n s a n d p H ra n g e s e m p lo y e d is a d d e d . I h e q u o tin g o f a m in im u m c o n c e n tr a tio n , a n d a c ritic a l c h o ic e o f t h e r e m a in in g c o n s t i t u e n t s c o m p ris in g t h e d i c h r o m a te , a b u ff e r a c id a n d a s a l t m i x t u r e to c o n tro l t h e p H i n t h e e ffe c tiv e ra n g e , a r e a ls o fe a tu r e s o f t h e p r e s e n t p a t e n t .

B .P . 450589 u ses a co ld s o lu tio n o f d i c h r o m a te a n d m a g n e s iu m s u lp h a t e . A n o b je c tio n t o i t is t h a t th e w o rk m u s t b e ra c k e d o u t o'f e le c tr ic a l c o n t a c t w ith t h e s u s p e n s io n a n d a lo n g t r e a t ­ m e n t tim e o f o n e to tw o h o u rs is n e c e s sa ry . B .P . 506836 d e s c rib e s a d ic h r o m a t e s o lu tio n c o n ta in in g c h r o m ic s u lp h a t e a n d is p re fe ra b ly u s e d a t b o ilin g p o in t. T h e p r e s e n t p a te n te e s s t a t e t h a t s u c h s o lu tio n s a r e u n s u ita b le a s h y d r o g e n io n c o n c e n tr a tio n c h a n g e s r a p id ly a n d t h a t t h e y t e n d to slu d g e .

B .P . 510353 c o v e rs a p ro c e ss w ith o r w i t h o u t th e a p p lic a ti o n o f e le c tr ic c u r r e n t, u s in g a c o ld a q u e o u s s o lu tio n c o n ta in in g ^ c h ro m ic -a c id io n s a n d io n s o f o n e o r m o re a c t i v a t i n g s a lt s . C o n ­ s t i t u e n t s a r e c h o s e n a n d p r o p o r tio n s a rra n g e d so t h a t w i t h a d d itio n s o f a c id o r a lk a li th e p H ra n g e re q u ire d fo r p ro d u c in g t h e d e s ire d film in t h e c o ld is a c h ie v e d in a m a x im u m of tw o h o u rs . T h e s o lu tio n is s u c h t h a t it s p H v a lu e is n o t c h a n g e d b y m o re t h a n tw o b y th e a d d itio n o f 12 g m s. o f p o ta s s iu m h y d r o x id e p e r litr e . T h e s p e c ific a tio n re v e a ls t h a t a c t i v a t i n g s a l t s a r e u s e d t o p r o v id e a b u ff e r in g e ffe c t o v e r t h e p H r a n g e 3-5 a n d t h a t t h e c h o ic e of c a tio n is o f fir s t i m p o r ta n c e . A lu m in iu m a lu m s o r a lu m in iu m s a l t s a r e p re f e rr e d , w h e re a s c h ro m iu m a n d iro n a lu m s a r e u n s u ita b le a n d n ic k e l a n d m a g n e s iu m s u lp h a t e s p a r t ic u la r ly u n s u ita b le . T h e a n io n o f t h e a c t i v a t o r s a lt s is o f le ss im p o r ta n c e a n d i t is s t a t e d t h a t i t m a y b e s u l p h a t e , n i t r a t e , c h lo rid e, o r o t h e r s a l t of a lu m in iu m , a lth o u g h t h e ch loride_ is n o t v e ry s a ti s f a c to r y . I n c o n t r a s t w i t h th is , t h e a n io n fo r t h e p r e s e n t p a t e n t is o f first im p o r ta n c e , b e c a u s e i t h a s a d if f e r e n t ro le t o fu lfil. A g a in , th e s a m e p a t e n t c la im s t h e u s e o f p o ta s s iu m o r o t h e r p e r m a n g a n a te , w h e re a s t h e p r e s e n t p a t e n t fin d s p e r m a n g a n a te s t o b e d e le te r io u s . T h e t r e a t m e n t t i m e is h a lf a n h o u r in t h e c o ld , b u t t h e s o lu tio n c a n n o t b e h e a t e d to s h o rte n t h i s p e rio d , o th e rw is e t h e s p e e d o f re a c t io n is to o r a p i d t o o b t a i n c o a t in g s o f g o o d a d h e r e n c e . C o n t r a s t e d w i t h th is , t h e p r e s e n t p a t e n t c a n y ie ld s a tis fa c to ry ' c o a t in g s in le ss t h a n 10 m in u te s in t h e c o ld .

September, 1 944 LIGHT M ETALS 415 B .P. 482689 and 510487

d e s c rib e t r e a t m e n t of

m a g n e s iu m a llo y s b y im m e rs io n in a h e a te d s o lu tio n of a lk a li d i c h r o m a te a n d n ic k e l s u l p h a t e , c h ro m iu m s u lp h a t e o r n ic k e l- a m m o n iu m s u lp h a t e , p lu s a n a c i d if y in g a g e n t w h ic h m a y b e a c e tic a c id o r a m m o n iu m a c e ta te . T h e f ir s t o f th e s e s p e c ific a tio n s s t a t e s t h a t , a t 35-50 d e g re e s C. t h r e e - q u a r te r s o f a n h o u r ’s im m e rs io n is n e c e s s a ry , w h e re a s a t 90-100 d e g re e s C. fiv e m in u te s is r e q u ir e d . A t t h e s a m e tim e t h e b a t h is le ss s ta b l e a t t h e h ig h e r t e m ­ p e r a tu r e s . A f u r t h e r o b je c tio n to th e p ro c e ss is t h e u se o f h e a v y m e ta l s a lts , a s th e r e is a lw a y s a te n d e n c y t o p ro d u c e in th e c o a tin g h e a v y m e ta l d e p o s it s w h ic h m a y g iv e rise to c o rro s io n . I n c o n t r a s t w ith th is , th e p r e s e n t p a t e n t g iv e s g o o d c o m m e rc ia l p ro te c tio n in a s h o r t tim e a t ro o m t e m p e r a tu r e , e v e n in o n e to th r e e m in u te s in c e r ta in c irc u m s ta n c e s . A g a in , w h e n h ig h e r te m p e r a tu r e s a re re q u ire d fo r s p e e d in g -u p t h e p ro c e ss , a s , fo r in s ta n c e , to f it in w ith o t h e r o p e r a tio n s , th e b a t h is s till s ta b l e . H e a v y m e ta l s a lt s a r e d e fin ite ly a v o id e d b e c a u s e th e y e ith e r fo rm h e a v y m e ta l d e p o s its in t h e c o a tin g , o r p r e c i p i t a t e d o r c o llo id a l m a t t e r w ith s p o n ­ ta n e o u s c h a n g e in p H . D o u b le d e c o m p o s itio n b e tw e e n th e b a t h c o n s t i t u e n t s m a y a lso o c c u r.

T h e o b je c t o f th e p r e s e n t p a t e n t is t o p ro v id e a n im p r o v e d p ro c e ss fo r th e p ro te c tio n of m a g n e s iu m - b a s e a llo y s u s in g t h e d ic h r o m a te m e th o d , in c o r p o r a tin g s h o r t t im e t r e a t m e n t a t ro o m te m p e r a t u r e , a v o id a n c e o f s tr o n g ly a cid b a t h s a n d t h e u se o f e c o n o m ic , s ta b l e s o lu tio n s . T o th is e n d , p a r t i c u l a r in g re d ie n ts a n d c o n ­ c e n t r a t i o n s a r e e m p lo y e d w h ic h c o n s t i t u t e a n e s s e n tia l a n d n e w c o m b in a tio n w ith r e s p e c t to t h e fo llo w in g fa c to r s :— D ic h r o m a te c o n c e n tr a ­ tio n , s u l p h a t e c o n c e n tr a tio n , h y d r o g e n ion c o n c e n tr a tio n a n d t h e u se o f a b u ff e r a g e n t , th e c a t io n s of a ll s a lts b e in g c h o se n to m e e t p a r ­ ti c u l a r re q u ire m e n ts a s fo llo w :— 1.— W ith in th e s p e c ifie d p H ra n g e , c a t io n s s h a ll b e s ta b l e in a q u e o u s s o lu tio n s a n d n o t u n d e rg o c h a n g e s o f t h e ir ow n a c c o u n t. 2.— T h e c a t io n s s h a ll b e s ta b l e in t h e p re s e n c e o f d i c h r o m a te io n s . 3.—

T h e c a t io n s s h a ll n o t r e a c t w ith o t h e r c o n s ti tu ­ e n ts in s u c h a m a n n e r a s to p r e v e n t th e a t t a i n m e n t o r m a in te n a n c e of th e s u l p h a t e a n d d i c h r o m a te io n c o n c e n tr a tio n s sp e c ifie d . 4.—

T h e c a t io n s s h a ll n o t r e a c t w ith m a g n e s iu m , o r fo r m o t h e r m e ta l d e p o s it s o n t h e s u rfa c e of th e m a g n e s iu m .

T h e e s s e n tia l re q u ir e m e n ts o f th e c la im a re :—

( a ) . D ic h r o m a te io n c o n c e n tr a tio n s n o t le ss t h a n 0.05 m o la r a n d p r e f e r a b ly b e tw e e n 0.2 a n d 0.5 m o la r. T h is re g io n is th e o p tim u m w h e n th e o t h e r fa c to rs a re a lso a t t h e i r o p tim a . C o n ­ v e n ie n t s o u rc e s o f d ic h r o m a te io n s to e n su re t h a t th e c a t io n s im u lta n e o u s ly in tr o d u c e d s h a ll s a ti s f y a ll t h e fo reg o in g r e q u ir e m e n ts , a r e t h e d i c h r o m a te s o f h y d r o g e n , lith iu m , s o d iu m , m a g n e s iu m , p o ta s s iu m o r a m m o n iu m . T h e s e m a y b e u s e d s in g ly o r in c o m b in a tio n . (b ) S u lp h a te io n s in c o n c e n tr a tio n in le ss t h a n 0.2 m o la r a n d p re fe ra b ly b e tw e e n 0.6 a n d 1.0 m o la r.

T h e m o s t c o n v e n i e n t s o u rc e s o f s u lp h a t e io n a r e t h e s u l p h a t e s o f h y d r o g e n , lith iu m , s o d iu m , m a g n e s iu m , p o ta s s iu m o r a m m o n iu m , s in g ly o r in c o m b in a tio n . S u lp h a te s o f a lu m in iu m , n ic k e l, c h ro m iu m a n d t h e a lu m s o f n ic k e l, a m m o n iu m , s u lp h a t e a r e n o t s u ita b le . W h e n a p ie c e o f m a g n e s iu m is im m e rs e d in a d ic h r o m a te s o lu tio n t h e m a g n e siu m r e a c t s w ith t h e

d ic h r o m a te a n d th e r e a c t io n p r o d u c ts fo rm a film on th e s u rfa c e w h ic h in h ib its f u r t h e r a t t a c k , b u t is to o t h i n to b e o f p r a c tic a l v a lu e w h e n th e s o lu tio n is w ith d r a w n . T h e film is h ig h ly p o ro u s a n d film fo r m a tio n w o u ld j)ro ceed f u r t h e r if m a g n e s iu m c a t io n s c o u ld d iffu se o u tw a r d s t h r o u g h th e p o re s . T h e y c a n o n ly d o th is if th e c o rre s p o n d in g a n io n s c a n d iffu se in to th e p o re s to p e r m it f u r t h e r d is s o lu t io n of m a g n e s iu m a n d c o n tin u e d film fo r m a t io n b y r e a c tio n w ith th e d ic h ro m a te . F o r s a ti s f a c to r y film fo r m a tio n i t a p p e a r s t h a t t h e r e m u s t b e a b a la n c e b e tw e e n in w a rd d iffu sio n o i a n io n s a n d th e r a t e a t w h ic h th e p r o te c tiv e r e a c t io n p ro ­ d u c t s c a n b e fo rm e d . T h e r a t e o f d iffu sio n of a n io n s in to t h e p o re s d e p e n d s 011 t h e i r size a n d c h a rg e a n d s u lp h a t e o n e s a re c la im e d to b e t h e o n ly s u ita b le o n e s in th is re s p e c t. C h lo rid e io n s a r e to o s m a ll, d iffu se to o q u ic k ly a n d c a u s e p ittin g . T h e s a m e is tr u e to a le sse r e x t e n t of

Fig. 4.—Curves showing relationship between duration of treatm ent an d subsequent

corrosion rate of the treated alloy.

b ro m id e io n s, a n d , w h ils t io d id e io n s m ig h t be s a t i s f a c t o r y , th e y a r e u n s u ita b le b e c a u s e th e y a r e o x id iz e d b y th e d ic h r o m a te . N i t r a t e io n s a r e a b o u t t h e s a m e size a s s u l p h a t e io n s, b u t h a v e o n ly a sin g le c h a r g e . N i t r a t e io n s w o u ld b e o x id iz e d . A ll o t h e r io n s a r e to o la rg e o r fo rm in s o lu b le re a c tio n p r o d u c ts w ith m a g ­ n e siu m w h ic h clo g th e p o re s a n d s to p f u r t h e r film fo r m a tio n . N o t o n ly is s u l p h a t e e ss e n tia l, b u t it s c o n c e n tr a tio n is i m p o r t a n t . F ig . 1 g r a p h ic a lly sh o w s t h e r e la tio n s h ip b e tw e e n s u l p h a t e c o n c e n tr a tio n in m o le s p e r litr e a n d c o rro s io n r a t e in e m p iric a l u n i t s e m p lo y in g u n ifo rm t r e a t m e n t tim e s . T h e r e is a n o p tim u m c o n c e n tr a tio n o f 0.26 to 1.0 m o la r. T h e re is l i t t l e lo s s in p ro te c tio n w i t h h ig h e r c o n c e n tr a ­ tio n s , b u t b elo w th is re g io n c o n c e n tr a tio n is c ritic a l a n d p ro te c tio n r a p id ly fa lls so t h a t less t h a n 0.2 m o la r is o f n o p r a c tic a l v a lu e , (c) A m m o n iu m io n s im p r o v e t h e p r o t e c t i v e v a lu e o f t h e film fo r a n y g iv e n tim e o f t r e a t m e n t . T h e c o n c e n tr a tio n is s u ffic ie n t if t h e a m m o n iu m s a l t b e u s e d fo r o n e o f t h e o t h e r in g re d ie n ts (a ) o r ( b ) . (d ) T h e r a t e o f film f o r m a tio n in c re a s e s w ith in c re a s e in a c i d ity o f t h e so lu -

E

416 LIC H T M ETALS September, 1944

Fig. 5.—Curves show ing optimum, minimum and* maximum pH values of bath for magnesium-base alloys of varying aluminium

content.

tio n . A t t h e s a m e tim e t h e w e ig h t o f m e ta l d is s o lv e d fro m th e w o rk p ie c e in c re a se s a n d , th e re fo re , d im e n s io n a l to le ra n c e s l im it th e p e r ­ m is sib le in c re a s e in a c i d ity . T h e p r o te c tiv e v a lu e is a lso a ffe c te d if a c i d i t y fa lls o u ts id e c e r ta in lim itin g ra n g e s fo r e a c h ty p e o f s o lu tio n . T h e effe c t o f p H v a r ia tio n u p o n p r o te c tio n fo r tw o p a r t i c u l a r a llo y s u s in g s o lu tio n s c o v e r e d b y t h i s i n v e n tio n is s h o w n in F ig . 2. T h e r e a re m a r k e d in d ic a tio n s o f a n o p tim u m p H v a lu e fo r e a c h a llo y . G e n e ra lly s p e a k in g , t h e o p tim u m d e p e n d s u p o n t h e a lu m in iu m c o n t e n t o f th e a llo y a s s h o w n in F ig . 3, w h ic h g iv e s th e r e la ­ tio n b e tw e e n h y d ro g e n io n c o n c e n tr a tio n a n d p e r c e n t a g e o f a lu m in iu m in a llo y s t r e a t e d w ith c e r ta in s o lu tio n s p f th is i n v e n tio n . T h e d e g re e o f p r o te c tio n fa lls off r a p id ly on e ith e r sid e of th e o p tim u m v a lu e s fo r e a c h a llo y , b u t a ll v a lu e s fa ll w ith in t h e e x tr e m e p H r a n g e of 4-6. T h e p H v a lu e s q u o te d w e re d e te r m in e d b y t h e g la s s e le c tro d e m e th o d ; o t h e r m e th o d s o f p H m e a s u r e m e n t m a y b e u se d , b u t a llo w ­ a n c e m u s t b e m a d e fo r v a r i a t i o n s fro m th e g la ss e le c tr o d e v a lu e s , (e ) B u ffe r a g e n t s . T h e m a in ­ te n a n c e o f p H v a lu e a t th e o p tim u m , o r w ith in t h e p e rm is s ib le r a n g e fo r a g iv e n a llo y , is c o m ­ p lic a te d b y t h e f a c t t h a t t h e p H ris e s a s m a g ­ n e s iu m d is s o lv e s d u r i n g tr e a t m e n t . F r e q u e n t c o n tro lle d a d d itio n s o f a c id a r e n e c e s s a ry , b u t c a n b e g r e a t l y re d u c e d b y in c o r p o r a tin g in th e s o lu tio n a w e a k a c id a n d o n e o f its s a lt s c a p a b le o f b u ffe rin g t h e s o lu tio n w ith in th e d e s ir e d p H ra n g e . A c e tic a c id is th e b e s t a n d c h e a p e s t o rg a n ic a c i d fo r t h e b u ffe r m ix tu r e , to g e th e r w i t h its s o d iu m o r a m m o n iu m s a lt. A n y o f th e o t h e r b a s e s lis te d b e fo re u n d e r (b ) m a y b e u sed f o r t h i s s a lt . A g a in , o t h e r w e a k a c id s o f s u i t ­ a b le d is s o c ia tio n c o n s t a n t a n d s a l t s o f th e m if o f su ffic ie n t s o lu b ility m a y b e u s e d in p la c e of, o r in a d d i t i o n to , t h e a c e tic a c id a n d a c e ta te . T h e b u ff e r a c i d m u s t n o t fo rm a n in s o lu b le s a l t w ith m a g n e s iu m a n d m u s t n o t b e o x id iz e d b y t h e d ic h r o m a t e in g r e d ie n ts . T h e fo llo w in g

s o m e w h a t d iv e r s e g ro u p o f a c id s, i t is c la im e d , is c a p a b le o f m e e tin g th e s e re q u ir e m e n ts :—

P r o p io n ic . M alo n ic.

B u ty r ic . S u c c in ic .

V a le ric . G lu ta ric .

P iin e lic . A d ip ic .

P h th a lic .

T h e b a t h c a p a c i t y is r o u g h ly p ro p o r tio n a l to t h e c o n c e n tr a tio n o f t h e w e a k a c i d a n d it s s a lt . P e rio d ic m a jo r c h a n g e s t o p H c a n b e s e c u re d b y a d d itio n s o f t h e m a jo r a c id o r a lk a li, n a m e ly , s u lp h u ric , c h ro m ic o r n itr ic a c id s , a m m o n ia , c a u s tic s o d a o r o t h e r a lk a li fro m t h e a b o v e lis t.

T h e a c id s a n d t h e i r s a lt s p r e fe rr e d fo r c o ld s o lu tio n s a r e s in g le o r m ix e d a c id s a n d sin g le o r m ix e d s a lt s o f th o s e a c id s o f t h e a c id g ro u p j u s t m e n tio n e d , th e c a t io n s o f t h e s a l t b e in g th o s e o f lith iu m , s o d iu m , m a g n e s iu m , p o ta s s iu m o r a m m o n iu m . F o r h o t s o lu tio n s th e s in g le o r m ix e d a c id s a n d s a lt s a r e c h o se n so t h a t th e b u ffe r a g e n t is s u ffic ie n tly s o lu b le a t t h e o p e r a t ­ in g t e m p e r a t u r e , a n d t h e fo llo w in g lis t is g iv e n of s u ita b le o n e s, t h e s a lt s b e in g o f th e s a m e b a s is a s b e fo re :—

O e n a n th i c . M alo n ic.

S u c c in ic . G lu ta ric . A d ip ic .

S u b e ric . P im e lic . B e n z o ic . P h th a lic .

W h e n i t is d e s ire d to s e c u re m a x im u m p o s­

s ib le p ro te c tio n , s u l p h a t e io n c o n c e n tr a tio n s h o u ld n o t e x c e e d t h e o p tim u m re g io n in d ic a te d b e fo re u n d e r (b ) a n d in s u c h c a s e s t h e m a jo r p H a d j u s t m e n t s h o u ld b e m a d e u s in g th e c h ro m ic o r n itr ic a c id a d d itio n s . A ll s a lt s e m p lo y e d fo r i n tr o d u c in g t h e d ic h r o m a te a n d s u lp h a t e a n io n s , th e s a l t o f th e b u ffe r a c id a n d t h e b a se fo r p H a d j u s t m e n t m u s t b e c h o se n so t h a t t h e i r c a t io n s m e e t th e fo llo w in g re q u ir e m e n ts :—

1.— W ith in t h e p H ra n g e 4-6 t h e y s h a ll re m a in in s ta b l e s o lu tio n in th e p re s e n c e o f d ic h r o m a te io n s, s u lp h a t e io n s a n d th e b u ffe r a c id . C a tio n s w h ic h d o n o t s a ti s fy th is re q u ire -

Fig. 6.—Curve showing relationship between anode current density in electro-chromate treatm ent, an d subsequent corrosion rate of

the treated alloy.

It

t