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FILE copy 
NO. 2-W 



N 82 661 97 

ARR July 1941 



NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 



WARTIME REPORT 

ORIGINALLY ISSUED 

July 1941 as 
Advance Restricted Report 

ALUMINUM-ZINC -MAGNESIUM-COPPER CASTING ALLOYS 



By L. W. Eastwood and L. W. Kempf 
Aluminum Company of America 

FILE COPY 

To be returned to 
the files of the National 
Advisory Committee 

for Aeronautics 
Washington, 0. C. 

NACA 



WASHINGTON 

NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of 
advance research results to an authorized group requiring them for the war effort. They were pre- 
viously held under a security status but are now unclassified. Some of these reports were not tech- 
nically edited. All have been reproduced without change in order to expedite general distribution. 




W-31 



AESTRACT 



The tensile properties and hardness of aluminum- z inc- 
magneaium- copper alloys containing approximately 0.25 per- 
cent chromium and C.15 percent titanium have "been investi- 
gated over a range of 0 to 1.75 percent copper, 3 to 13 
percent zinc, and 0 to 1.0 percent magnesium. The chro- 
mium and titanium xvere added for their specific effects 
on resistance to corrosion and grain refinement, respec- 
tively. Aluminum ingot which contained approximately 
0.15 percent iron, C.OS percent silicon, and 99.75+ per- 
cent aluminum was used as a "base. In sand castings, ap- 
proximately 0.4 percent copper, 6.6 percent zinc, 0.33 
percent magnesium, 0.25 percent chromium, and 0.15 percent 
titanium appear to give a good combination 0 f strength and 
ductility together with satisfactory resistance to corro- 
sion. Such an alloy a;;es at room temperature without any 
previous heat treatment and attains high tensile proper- 
ties, endurance limit, resistance to failure "by impact, and 
good resistance to corrosion in tne accelerated tests 
utilized in this investigation. Castings of this type of 
alloy, however i nave t;ie disadvantage of "being somewhat 
'■hot short. 11 Its tensile properties at elevated tempera- 
tures are relatively lo^, and it overages With the conse- 
quent loss of tensile strength and hardness when exposed 
for a few months at temperatures as lo*^ as 212° ?. At 
300° F thifi overaging effect is rapid with consequent 
marked deterioration of the tensile properties and ttard- 
n e s s • 



alukiitum- z i ec- Magnesium- copper casting alloys 

Ey L. W. Eastwood and L. If. Eempf 

Aluminum- case alloys containing a high zinc content 
were among the first aluminum alloys used for castings. 
Because they Fere used in the early years of the aluminum 
casting industry, particularly in Europe, their history 
presents an interesting chapter in the commercial develop 
meat of this metal. The principal early investigation of 
"binary and more complex aluminum- z inc alloys was done by 
Rosenhain and Archbutt (reference l) in 1912. An excel- 
lent review including an extensive bibliography of the 
early development of aluminum- z inc alloys was published 
by the Bureau of Standards (reference 2) in 1927. 

The high zinc-aluminum alloys most widely used in 
Europe contained 10 to 14 percent sine and 2 to 3 percent 
copper, largely as a result of the work of Rosenhain and 
Archbutt. In the United States, Zay Jeffries and William 
A. Gibson (reference 3) developed an alloy containing 10 
to 12 percent zinc, approximately 2 percent copper, and 1 
to 1.75 percent iron, which was used quite extensively 
during the decennium 1920-30. In addition to aluminum- 
copper- iron- z inc alloys, these investigators in 1919 also 
pat ent ed aluminum-copp er- iron- magne sium- z inc a 1 loy s , a 
preferred composition of which was given as 7 percent zinc 
3 percent coprer, 0 to 1.5 percent iron, and 0.1 to 0.3 
p ere ent magne sium. 

Early in 1921, the production of heat-treated cast- 
ings began (reference 4) in the United States, and their 
continued development and use has been accompanied by the 
gradual displacement of the high zinc-aluminum alloys. 
This replacement by the heat-treated alloys occurred be- 
cau.se of their higher tensile properties, lower specific 
gravity, better casting characteristics, and greater re- 
sistance to corrosion. 

Aluminum alloys containing zinc and magnesium as the 
principal alloying ingredients have also been in commer- 
cial use. At an early date, William Guertler and ffilhelm 
Sander (reference 5) investigated and proposed the use of 
aluminum alloys containing magnesium and zinc in the -pro- 
portions in which they occur in the compound MgZn 2 . 

Alloys of this tyre have been used commercially for a num- 
ber of years. (See reference 6.) For example, an alloy 
known as "Constuctal 8 11 containing 7 percent zinc, 2.5 
percent magnesium, and 1 percent manganese was first 



2 



proceed in Germany aTaout two decades ago* A similar 
alloy developed by William Guertler for castings con- 
tain!. £ 7 . £ percent z i nc and 1,7 percent rnaf r.3 9 i&JS , has 
been desi^ated G.W.32. Another containing 6 percent 
zinc, 1.2 p sr cent rna.^r es iun, and ? o-rcent iron was de- 
veloped by T . 3. Fuller and David Basch (reference 7) in 
the United States. 

In 1937 and 1%33 B. series of United States patents 
was issued to Yo nc si-he Mai ue nag a ( r of .r encr 3) on aluminum 
alloys containing ziv..e, magnesium, and copper as the Prin- 
cipal alio yi ng constituent" , Aluminum- ? inc-ma^n-j s ium al- 
loys having a preferred composition of 3 . r > percent sine, 
0*5 percent chromium, 0.20 percent ffia^nesiumg 0.10 percemt 
titanium, less than D P J percent copper, silicon or $yaaga- 
nese and less than 0.5:' Percent iron have "" en 'oro^osed by 
Georje I 1 . Corns took. (See reference 9 • ) Ther e have "been 
many other investigation- 4 of a Ium i nun .alloys containing 
?inc and. ma^ne 3 iv,m a^ the •.••rinci^al alloying, constituent^., 
"but a complete rev lev here 5 s unnecessary. . 

This p«per contains data on the mechanical properties 
of sand- cast test bar s h^vhi;- a considerable ran;- 2 .in Tine , 
raa^nenun, and co;v':er content ^nd more detailed data on 
the properties and four.dr" r ch?-raot sr 1st ic£ ? of an aluminum- 
i nc- mag n e 0 ium- c opr; er alloy having a preferred co mp o 3 i t i on 
for high strength and duct ? iity , The principal portion of 
the data is on alloys > r hich also contain ap- r oximat ely 0.1*3 
percent of t i t anium and 0 • °n Percent el'romiur.. The tita- 
nium and chromium were added because the rr "qr e found, to 
effect go*ain refinement ?nd improve resistance to corro- 
sion, respectively, 

3XF5HIKE17TAL FHOC^DU.IE 

P r ep an a t i on 0 f t h e Alloys 

Aluminum in^ot containing Q 3*7? percent aluminum .---nd 
the alley components were car efully weighed. The magne- 
sium and *iuc were added as rv.ch, but the chromium, tita- 
nium, and popper were added in the form of aluminum-base 
riches prepared with 3 9 • S percent aluminum. The melts 
M ere made in plumbago crucibles In gas -fired furnaces. 
First the aluminum WM melted down, and th :n the alloying 
material, except the magnesium, was add :d and melted. 



3 



The melt was fluxed with chlorine for 10 to 15 minutes, 
and then the magnesium was added. If a variation in the 
content of magnesium, zinc, or copper was desired, these 
metals were successively added in the proper amounts after 
eaeb set of the test castings had teen poured. Each set 
of castings in the series was then given the same heat 
number, with the letters A, B , C, etc., attached in the 
order of pouring. 

ft 

Test Castings 

Cast- 1 'o- s ize test bars rere made using a 6- "bar cast- 
ing, a photograph of which la shovrn in figure 10. These 
test bars are 1/2 inch in diameter at the test section. 
The test-bar castings used for corrosion tests were cast 
somewhat oversize and machined to i/3 inch diameter at the 
test section. A casting having heavy sections was used to 
determine the effect of section size. This casting is 
shown in figure 11 with the gates and risers attached. 
Each section is 6^/4 inches long, 4 inches wide, and 1, 2, 
and 4 inches thick. Test bars 0.505 inch in diameter at 
the test section were machined from this casting. All 
castings were poured from 1350° 1 unless otherwise not ed, 
and all were made in green sand molds. 



Aging Treatment 

After the castings were made, they were aged as in- 
dicated by the data in the tables or figures. Usually the 
castings were aged for 30 days at a room temperature main- 
tained at about 85° F . In some instances- an equivalent 
aging treatment was effected by using a shorter time at a 
slightly elevated temperature. This subject is treated 
more fully elsewhere int his paper. 

Corrosion Tests 

Corrosion tests were made on separately cast test 
bars. The investigation of the corrosion of test bars 
under an applied stress was conducted by using the ex- 
perimental procedure described by E. E. Dix, Jr. (See 
r ef er enc e 10 . ) 

The general corrosion characteristics of unstressed 
bars were determined in salt-spray exposures in a manner 



4 



described "by E . K. Dire, Jr. and J. J. Bowman, (See refer- 
ence 11.) The equipment used is illustrated by figures 1 
and 3 of their paper "Salt Spray Testing." Hard rubber 
spray nozzles were employed, and the salt- spray boxes con- 
tained six vents each. The air at 40 pounds per square 
imch was passed through a cleaning to"<er and tnen through 
a water column maintained at 85° J to saturate it at the 
test temperature before it entered the boxes. The salt- 
spray exposures, maintained at 35° F, were of two types, 
continuous and intermittent. A 20-percent -salt solution 
was used for the continuous exposure and a 3 Vb-percent - 
salt solution for the intermittent exposure, Morton's 
Flake Butter Salt being used for both types. The inter- 
mittent cycle comprised 16 hours with the box closed and 
the spray operating, and 8 hours with the box open and 
the spray not operating, 

Six cylindrical test bars made in green sand and ma- 
chined to 0.5 inch at the test section were suspended from 
glass rods for each type of exposure. In order to remove 
dust and grease which might have interfered with the test, 
the bars were cleaned in petroleum ether before starting 
the exposures. 



Tensile and Hardness Tests 

Except those made on heavy sections, all tensile 
tests were made on separately cast test bars without ma- 
chining the gb&e section. Yield-strength values were ob- 
tained at the point of 0,2-percent deviation from the mod- 
ulus line. 

Erinell hardness was obtained by using a 500-kilogram 
load and a 10 -mi 11 imet er ball. 

Elongation values were determined on a 2-inch gage 
length. 

EXPERIMENTAL RESULTS 



The experimental results obtained are presented in 
the accompanying tables and figures. The effects of zinc, 
magnesium, and copper content on the tensile and hardness 
properties of cast test bars have been investigated over 



5 



a considerable range. She resistance to corrosion of 
these alloys under an externally applied stress also has 
teen investigated. A relatively narrow concentration 
range of zinc, magnesium, and copper has been more thor- 
oughly investigated in respect to aging characteristics, 
effects of exposure to elevated temperatures, high- t emp er- 
ature tensile properties, tensile properties in heavy sec- 
tions, foundry characteristics, and physical properties. 

The Effect of Zinc, Magnesium, and Copper Content 

The effects of the magnesium content on the tensile 
strength, percent elongation in 2 inches, yield strength, 
and Brinell hardness of alloys containing 3 to 13 percent 
zinc and approximately 0,4 percent copper, 0.25 percent 
chromium, 0.15 percent titanium, 0.15 percent iron, and 
0.08 percent silicon are shown by figures la, lb, 1c, and 
Id, respect ively. Data on similar alloys containing 1.0 
percent copper instead of 0.4 percent are graphically rep- 
resented by figures 2a, 2b, 2c, and 2d, respectively. A 
third set of data on a series containing 1.75 percent cop- 
per is represented by figures 3a, 3b, 3c, and 3d. 

By the use of curves which represent the tensile 
strength and percent elongation, it is possiole to deter- 
mine the maximum and minimum amounts of magnesium at each 
zinc content which will give desired minimum values of 
tensile strength and elongation. This has been done for 
certain values, and the results are represented graphi- 
cally by figure 4. This figure shows the range in zinc 
and magnesium content at which minimum tensile properties 
of 36,000 pounds per square inch and 10-percent elongation, 
and 34,000 pounds per square inch and 7- percent elongation 
were attained under the experimental conditions utilized. 
The former minimum values of tensile properties are rep- 
resented by the inside area bounded by full lines, and 
the latter values by the entire area bounded by the dashed 
1 ine s . 

Examination of figure 4 shews that the higher the 
zinc content, the lo^er the magnesium content for maximum 
combinations of strength and ductility. The shape of the 
areas representing the zinc and magnesium concentrations 
for minimum tensile properties of 33,000 pounds per square 
inch and 10-percent elongation is quite similar at each of 
the three values of copper content represented. However, 



6 



increasing the copper content decreases the size of areas 
representing the range of magnesium and zinc for these 
minimum properties; and for a given zinc content, increas- 
ing the copper requires decreasing magnesium concentration. 

Table I shows, for three series of alloys containing 
0.4, 1.0, and 1.75 percent copper and 4 to 13 percent zinc, 
the magnesium content required for the attainment of 36,000 
pounds per square inch tensile strength and 10 percent elon- 
gat ion . 

as indicated in figure 5, increasing the zinc content 
increases the tensile and yield strengths and hardness, 
hut decreases the elongation of alloys containing approxi- 
mately 0.35 percent copper, 0.15 percent iron, 0.08 per- 
cent silicon* 0.13 percent titanium, 0.25 percent chromium, 
0.27 and 0.29 percent magnesium. 

The Effect of Iron and Silicon Content 

Iron and silicon may he regarded as impurities since 
they do not improve the saachanical properties. These ele- 
ments invariably occur as impurities in aluminum. Accord- 
ingly, it is desira/ble to know the effects of these impur- 
ities on the properti.ee. The available data listed in 
table II, though not extensive, show the effects of iron 
and silicon separately and in combination. Figure 6 also 
shows that increasing., concentrations of silicon have a 
very adverse effect on the tensile strength and ductility 
of alloys containing. 0 • 38" ^percent copper, 0.15 percent 
iron, 6.6 percent zinc, 0.13 percent titanium, 0.2 percent 
chromium, and O-.0 8, 0.13-, and 0.33 percent silicone Iron 
alone has only a slightly adverse effect on the tensile 
prop-e-rties even when 0.5 percent is present • When iron 
and silicon are increased simultaneously, the tensile 
strength and ductility ar<r reduced to aborut the same ex- 
tent as tney would be if the silicon alaaa were increased 
The adverse effect of silicon is probably due to- the for- 
mation of Mg 2 S.i. .which depletes" the- effective .jaa&aasium 

content and forms a. ..brittle grain boundary-' cons-t. it uer.t . . . 
With the. aluminum at present commercial ly available, it 
" pro-bail y is not practical to specify -silicon _c<mcan.t ra- 
tions lower taan about 0.25 percent, The mecn-anical prtrp~- 
erti.es of commercial castings "might be-expected to be 
lower tnan those obtained in this inv-est igjati.Q_n~ on jal lsy^ 
co nt aining . abctrt 0.08 percent . -s.il iccn- in, a_bou_t ±he.-rxit io - 
indicated ;Ln table II- 



7 



Resistance to Corrosion 

Four alloys were exposed in salt spray in the manner 
described above. Two of these alloys contained approxi- 
mately 7 percent zinc, 0.3 percent magnesium, 0.15 percent 
iron, 0.08 percent silicon, 0.15 percent titanium, 0.35 
percent copper, and 0.00 percent chromium. One of these 
was prepared from 99.99+ percent zinc, and the other from 
99.5 percent zinc. The other two alloys were similar in 
composition to the first two described, but both were made 
with 99.99+ percent zinc and both contained 0.25 percent 
chromium* One of these two contained 0.35 percent copper 
and the other, 1.0 percent copper. The results obtained 
after one year of exposure of unstressed cast test bars 
to continuous and intermittent salt sprays are as follows: 

1) The resistance of the alloy containing 0.25 per- 

cent chromium is superior to that of the chro- 
mium- free alloy. 

2) The alloy containing 1.0 percent copper appeared 

inferior to that containing 0.35 percent copper. 

3) The resistance to this tyoe of corrosion is not 

noticeably affected by the degree of purity of 
the zinc. 

4) An alloy containing approximately 0.35 percent 

copper, 0.15 percent iron, 0.08 percent silicon, 
7.0 percent zinc, 0.15 percent titanium, and 
0.25 percent chromium has good resistance to 
this type of corrosion; it is about equivalent 
to the well-known Alcoa no. 43 alloy consisting 
of aluminum with 5 percent silicon. 

It has also been found that bars stressed at 75 per- 
cent or less of the yield strength are not subject to in- 
tergranular corrosion when continuously immersed in a solu- 
tion of NaCl and E 2 0 2 , provided the zinc does not exceed 
about 7.0 percent and the copper is not less than 0.25 per- 
cent or more than 0.5 percent. 



Preferred Compos it ion 

On the basis of the results on tensile properties and 
resistance to corrosion discussed above, an alloy contain- 
ing approximately 0.4 percent copper, 0.15 percent iron, 



6 



0.08 percent silicon, 6.6 percent sine, 0 • 33 Percent mag- 
nesium, 0.15 percent titanium, and 0.25 percent chromium 
was selected for more detailed investigation. 



Aging Char act erist ics 

Table III and figure 7 show the changes in tensile 
properties and hardness of cast test bars of an alloy con- 
taining: 0.38 percent copper, 0.17 percent iron, O.OS per- 
cent silicon, percent ~inc, 0.12 percent titanium, 
0.27 percent magnesium, and 0,?3 percent chromium. Three 
different aging ter^eratur^ were used, that is, 85°, 
I65 0 , and 21?° ?• The curves of figure 7 shov/ that the 
best combination of tensile strength and ductility is at- 
tained "by aging at 35° F * *t Will he noted that 1 week 
at I65 0 F is approximately equivalent to 1 month at S5 0 F. 
This alloy overages even at 212° I when the time at tem- 
perature is of several months 1 Curat ior. Cverarinf mani- 
fests itself "by a /\r';atly reduced ductility and some c.rcr) 
in yield strength and hard n e s s . After Z months at Ion F . 
there is no softening noticeable, hut the ductility as 
measured "by the percent elongation is freatly reduced. 
This might be compensated by starting out with a lower 
magnesium content and higher initial ductility. 



Tensile Properties in Heavy Sections 

Table IV contains data on the tensile properties in 
heavy sections of an alloy having about the preferred com- 
position referred to above. These data clearly show that 
a very high percentage of the Properties obtained in sep- 
arately cast test bars is obtained in bars machined from 
thir, 18-pound casting having sections 1, 2, and k inches 
t hi ck . 

High- Temper at ur e Tensile Properties 

The tensile strength and elongation of an alloy con- 
taining 1,00 percent copper, 0.1b percent iron, O.OS per- 
cent silicon, 6. 89 percent fine, 0.13 percent titanium, 
0.2o percent magnesium, and 0.27 percent chromium at 200°, 
300°, U00°, 500°, and 600° F are shown by the d*ta in 
tablo V. The elongation at room temperature for the par-* 
ticular lot of test specimens used for the determination 



9 



of these data and those of ta"ble VI, referred to in the 
next paragraph, is lower than normal for some unknovm 
reason. nevertheless, the conclusion is probably t vas~ 
t if led in that the high temperature properties of this 
type of alloy are somewhat inferior to those of many pres- 
ent day commercial aluminum-casting alloys. 

Effect of Prolonged Exposure at 300° and UOO 0 F 

Table VI shows the effect of ;orolonged exposure at 
300 :i and ^00° P on the tensile and hardness Properties of 
the alloy referred to In the preceding paragraph. These 
data show that exposure to such temperatures has an ad- 
verse effect on the room-temperature tensile properties 
"because of the overagin^ effect . 

Effect of Exposure to a T er.p er atr r e 

ITear the Melting Point 

Alumi num- z i nc-magnes ium-c opp er a 11 0 ys can "be r eheat ed 
to t er.p er at u r es near the melting point without a marked 
adverse effect on tensile properties. Table VII shoitfs the 
effects of reheating a specific alloy to temperatures from 
Q0 r -° to 1120° F, air cooling, and re-a^ing at room temper- 
ature. These data show that reheat lag to Q00° f has a 
slightly adverse effect on the tensile properties, whereas 
reheating to IO5O 0 to 1120° F does not affect the tensile 
properties. Of course, -hen this alloy is reheated to 
such temperatures, the tensile properties are about equiv- 
alent to those obtained immediately after casting, and re- 
aging is necessary to restore them. The amenability of 
these alloys to reheating to a high t emr> -;r at ur e makes them 
attractive for use in furnace-brazed assemblies. * 

Mechanical and Physical Properties 

Using the experimental conditions outlined, an alloy 
containing approximately O.35 percent copper, 0.15 percent 
iron, 0.03 percent silicon, b,6 percent ?inc, 0.1? v.ercent 
titanium, 0.3"^ percent magnesium, and 0.?R percent chro- 
mium may be expected to have approximately the following 
mechanical and physical properties in separately cast teat 
bars poured in £reen sand and aged JO days at ?5° ?. 



10 



Yield strength 
Tens i le s t r en, :th 



Blougat ion 



Br inell hardness 
Endurance limit 
C harpy impact value 
Solidification rang e 

Specific gravity 



21,000 pounds per souare inch 
36,00c pounds per souare inch 
10 percent in 2 inches 

66 to 70 

75OO pounds per souare inch* 

3.5 foot Pounds** 

6 5? ° C (l2bb° 7) to 610° C 
' (1130° f) 

2. SI 



Electrical conductivity 2?.; percent I.A.C.3. 

Inasmuch as iron and silicon concentrations of 0.15 
percent and O.OB percent, respectively, probably cannot 
•be maintained in ordinary foundry practice with aluminum 
of the purity at present generally available, it Is to he 
expected that minimum specification values for mechanical 
properties of this typs of alloy must he considerably 
lower than those given in the foregoing. The highest- 
purity aluminum- casting alloys at present in commercial 
use are produced to maximum silicon concentrations of 
about 0.25 percent. Under similar conditions, it is be- 
lieved that this type of alloy oo^id be produced to mini- 
mum tensile specifications of 30 , 000-p ounds-p er- s quar e~ 
inch tensile strength and -o-percent elongation. The prop- 
erties of the alloy are much less sensitive to iron con- 
centration, and a maximum somewhere between $•§ percent 
and 0.75 -oerccnt probably will he found permissible. 



Mler ©structure 

The micr ostructia re of the aluminum- % inc-ma^n^s ium- 
copper alloys are illustrated by th- photomicrographs 

*S. S, Moore rotating bean typo of machine, ^00,000,000 
c vol es .. 

** Modified Chrrpy impact machine, 10 mm x 10 mm keyhole 
type, drilled and sawed, notched specimens, section 
hack of the notch 5 mm X 10 mm, 5.07-pound hammer. 



11 



(figs. 8a, 8t>, 8c, and 8d) . The compositions of the alloys 
photographed are given in the captions to these Illustra- 
tions. Figures 8a and 8b snow similar specimens cut frcm 
the cope side of 4-inch sections of the step casting illus- 
trated "by figure 10. The alloy shown in figure 8a con- 
tained 1.05 percent copper, while that in figure 8b con- 
tained 0.34 percent copper. In figure 8a the dark areas 
brought out by Keller J s etch (reference 13) are rich in 
copper and they also contain light particles of CuAl 2 
precipitate. The lower copper alley shown by figure 8b 
does not have a noticeable amount of copper segregation. 
Such structures are usually accompanied by superior tensile 
properties in heavy sections or in castings otherwise sub- 
jected to abnormally slow solidification. This type of 
structure also appears more resistant to corrosion than 
one exhibiting particles of copper constituent. There is 
a considerable difference in the grain size between the 
two specimens of figures 8a and 8b, probably due in part 
to the higher titanium in the finer-grained specimen and 
in part to the inevitable variations in the structure of 
castings. However, the specimens illustrated are fairly 
typical of the effects of the amount of copper content on 
the microst ructure in heavy sections. In chilled sections 
or light sections where solidification is more rapid, this 
type of copper segregation is less pronounced. 

In general, the high-purity alloys of the composition 
photographed consist essentially of a solid solution which 
is subject to precipitation hardening at low temperatures. 
Only a very small amount of visible undissolved microcon- 
stituents occur. The principal microco ns t i tuent s which 
form visible particles in alloys of the composition photo- 
graphed are the Al-7e-Si constituent which usually" oc- 
curs at the grain boundary, but it may not occur in the 
typical "Chinese script 11 form, probably because of its 
small amount. A very small amount of CuAl 2 particles 
occur Within the grain or at the grain boundaries where 
the final solidification took place. Some Mg c 3i parti- 
cles, recognized under the microscope by their bluish 
color, occur as isolated particles or in conjunction with 
the other constituents. The constituents in the alloy 
have been identified by the methods outlined by E . H. 
Six, Jr. and J . Eeller. (See reference 13.) 



12 



Foundry Char act eris t ics 

Although the foundry experience obtained on an 
aluminum-zinc-magnesium-copper alloy having the preferred 
composition mentioned above is not extensive, some esti- 
mate of their foundry cnaract eristics can he made. 

It has been well established that the tensile prop- 
erties of test bars or of bars machined from 1- inch sec- 
tions are not affected by pouring temperatures between 
1300° and 1450° f« When the pouring temperature is low- 
ered to 1250° F or raised to 1500° F, a very slight de- 
crease in tensile properties occurs. 

The fluidity at 1350° and 1450° F has been determined 
in the manner formerly described (reference 12) and found 
to oe somewhat inferior to many aluminum alloys now in use. 
However, this difficulty can be offset by employing a 
slightly higher pouring temperature since no adverse ef- 
fect is encountered by this procedure. 

Data on tensile properties in heavy sections have al- 
ready been presented, and it was previously noted that a 
high percentage of test-bar properties is obtained. 

The alloy must be well risered to prevent shrinkage, 
but in this respect it does not differ from some alloys 
now in commercial use. 

The foundry characteristic which probably would 
cause the most trouble is hot- short nes s , In this respect 
it is about a3 subject to ho t- cracking as some of the 
aluminum- copper alloys now in use. Therefore, very intri- 
cate types of castings might be expected to be difficult 
to produce in this alloy. 

Voiding and Brassing Characteristics 

It has been pointed out that the alloy having the 
preferred composition is not adversely affected by heat- 
ing to a temperature near the melting point if it is al- 
lowed to re-a^e subsequently. Furthermore, the high-ten- 
sile properties of this alloy are attained without heat 
treatment so that, in consequence , it can be welded as 
readily as the other as-cast alloys and will still retain 
its high-tensile properties. The alloy also is readily 
furnace-brazed, since a brazing temperature up to 1100° F 



13 



can be used. Accordingly, this aluminum-zinc- magn esium- 
eopper type of alloy presents the possibility of utiliz- 
ing welded and brazed -assemblies of castings having ex- 
ceptionally high strength, toughness, and resistance to 
corro sion. 

SUMMARY 



The tensile properties of a luminum- z inc-magnesium- 
COpper alloys have been determined over a range of 0 to 
1.75 percent, copper, 3 to 13 percent zinc, and 0 to 1.0 
percent magnesium. An alloy containing 0.4 percent cop- 
per, 0.15 percent iron, 0.08 percent silicon, 5.6 percent 
zinc, 0.33 percent magnesium, 0.25 percent chromium, and 
C.15 percent titanium appears to have the maximum combi- 
nation of strength, ductility, and resistance to corro- 
sion and has been investigated in greater detail. 



Aluminum Research Laboratories , 

Aluminum Company of America, 
Cleveland, Ohio 



14 



REF3BSNCSS 



1. Ho senile in, W. , and Archbutt , S. L« l Alloys of Aluminum 

and Zinc. Inst. Mech. Eng. 1-2, 1912, pp. 319-515. 

2. Anon.: Light Metals and Alloys. Circular of the 

Bureau of Standards, No. 346, 1927. 

3. U.S. Patent Kos. 1,352,271 and 1,352,272 to Zay Jeffries 

and 7/illiam A. Gibson. 1920 

4. Archer, E . S., and Jeffries, Zay: Aluminum Castings of 

High Strength. Free. Inst, of Metals Div. A. I. M.S., 
1927, p. 35. 

5. U.S. Patent No. 1,629,699 to William Griiertler and 

William Sander. 1927. 

6. Zeerleder, A. von: The Technology of Aluminum and Its 

Light Alloys, IJcrdemann publishing Co., Amsterdam, 
1936. 

7. U.S. Patent jSfo • 1,760,549 to T. S. Fuller and David 

Ea sch . 19 30 . 

8. U.S. Patents Uos. 2,090,894, 2,090,895, 2,109,117, 

and 2,116,273 to Yonosuke Katuenaga. 1937 and 1938. 

9. U.S. Patents Nos. 2,146,330 and 2,146,331 to George F. 

Comstocic. 1939. 

10. Dix, E. II., Jr.: Trans. A.I.M.E. 137^, 1940, p. 11. 

11. Dix, B . H. , Jr., and Bowman, J. J.: Salt Spray Test- 

ing, Symposium on Corrosion Testing Procedures. 
A.S.T.M. , 1937. 

12. Eastwood, L. .7. , and Eempf , L. W.: The Measurements 

of Fluidity of Aluminum Casting Alloys. Trans. 
a.F.A. 47_, 19 39, p. 571. 

13. Dix, B . H. , Jr., and Keller, F. : Metals Handbook 

A.S.K., 1939, pp. 1290-1294. 



NACA 



Tables 1,6 



TABLE I 

THE MAGNESIUM CONCENTRATION AT VARIOUS ZINC AND COPPER CONTENTS 
FOB ATTAINMENT OF 36.000 PSI. TENSILE STRENGTH AND 10% ELONGATION 





0.4%Cu 


1.0% Cu 


1.75%Cu 




Optimum Magnesium Content 


% Zn 


&Js 






5 


0.54 






6 


0.42 


0.41 




7 


0.31 


0.29 


.16 


8 


0.20 


0.15 


.07 


9 


0.12 


0.06 


.02 


10 


0.07 


0.02 


.01 


11 


0.04 


0.005 


.005 


12 


0.005 







TABLE a 

THE EFFECT OF EXPOSURE TO 300°F AND 400°F OH THE ROOM TEMPERATURE 
TENSILE PROPERTIES OF CAST TEST BARS 'OF AN ALLOY CONTAINING 
1.06% Cu, 0.16% Fe, 0.08% Si. 6.89% Zn, 0.13% Ti, 0.26% Mg 

AND 0.27% Cr 



Txeatnjeqt 


_ ?j 

Y.5. 


: op.erti 
T.S. 


es _ 
%EL. 


"BHR 


6 Mo. at R.T. 

2 " " " ♦ 100 days at 300°F ♦ 2 mot at R«T.** 
2 « ♦ 50 11 " 400°? ♦ 3 " 11 " 


27800 
20200 
13700 


38400 
28050 
26600 


5.5 
5.7 
7.7 


82 
60 
54 



*Mo. ■ Months 
*B.T. ■ Room Temperature 



W-31 



TABLE H « 

o 



THE EFFECT OF IRON AND SILICON CONTENT ON THE TENSILE PROPERTIES > 
OF TEST BARS OF Al-Zn-Mg-Cu-Ti-Cr ALL575 



Section A 
Effect of Sllleon Content 



Heat 
No* 


A^ing Time 


Cu 


Fe 


Si 


Zn 


Tl 




Cr 


Y.S. 


T.S. 


#E1. 


BHN 


555 
556 
557 


30 days at 85°F 

V II 
H If 


0.32 
0.37 
0.37 


O.H 
O.H 
0.15 


0.08 
0.19 
0.33 


6.65 
6.58 
6.51 


0.13 
0.13 
0.13 


0.33 
0.32 
0.33 


0.24 
0.20 
0.22 


21700 
21600 
23100 


38200 
34900 
33950 


12.8 
10.2 
6.2 


73 
70 
74 


06 3A 
B 
C 


IT 11 
1* it 
II H 


0.003 
* 

* 


0.24 
* 


0.08 
0.18 
0.30 


6.80 
* 

* 


0.18 
* 

♦ 


0.31 
* 


0.00 
0.00 
0.00 


21800 
20000 
19800 


35200 
31800 
30000 


9-5 
8.2 

6.3 


74 
69 
70 



Section B 
Effect of Iron Content 



06 2A 


30 days at 85°F 

M 11 


0.003 


0.29 


0.10 


6.91 

* 


0.15 


0.28 


0.00 


22000 


36200 


10.2 


74 


B 


• 


0.46 


* 


* 


* 


0.00 


21600 


36600 


10.7 


74 


C 


II 1» 


* 


0.56 


* 


* 


* 


* 


0.00 


20400 


35300 


9.0 


73 



Section C 
Effect of Ingot Purity 



067 
069 


30 days at R.T.** 

11 « 


0.01 
0.01 


0.11 
0.33 


0.12 
0.16 


7.06 
7.13 


0.16 
0.16 


0.37 
0.36 


0.00 
0.00 


23100 
22300 


36300 
34100 


9.0 
7.3 


74 
74 


409 

413 


« n 
»i ti 


0.30 
0.27 


0.16 
0.23 


0.07 
0.10 


6.98 
7.00 


0.18 
0.18 


0.26 
0.26 


0.23 
0.25 


20300 

20200 


36600 
35350 


13.3 
11.7 


69 
69 


410 
412 


« 11 
» «t 


0.32 
0.32 


0.30 
0.32 


0.14 
0.14 


6.96 
6.95 


0.19 
0.23 


0.27 
0.30 


0.24 
0.24 


20300 
210O0 


34900 
35200 


9.8 
9.2 


69 
70 



The chemical analysis may be assumed to he approximately the same as the A sample except as noted* £ 
Room temperature. 



NACA 



Table 3 



TABLE Jt 

THE CHANGS IN TENSILE PROPERTIES OP CAST TEST BARS OF All 
Al-Zn-Mg-Cu-Ti-Cr ALLOY WITH AOINO TIME AT 
VARIOUS TEMPERATURES 



Heat 
HO. 



559' 



Aging Treatment 



1 
3 
7 
31 
60 
90 
182 
307 



hour after easting 
days at 85°ff 



M 
II 

m 
m 



1 hour after casting 
2-1/2 " at 165** 



19 
68 

6 days 

10 " 

14 " 

21 " 

31 " 

45 " 

60 " 
90 



If 
II 

tl 
11 
tl 
II 

H 
II 
II 

11 



1 hour after casting 
3 " at 212°F** 

20 " " 
69 

6 days 
10 

14 * 

21 » 

31 ■ 
36 
60 

70 



ii 
ti 
ti 

w 
N 
tl 
it 



XHS- 



6550 
15375 
17575 
20325 
21250 
21925 
23100 
23200 

6550 
10675 
17100 
20975 
23675 
24600 
26600 
26600 
28000 
28450 
28800 
30000 

6550 
10825 
17125 
21525 
25325 
26825 
27550 
26300 
29025 
29050 
28600 
28650 



T.S. 



20875 
30425 
33350 
35575 
35800 

35925 
37850 
37800 

20875 
24675 
31500 
33550 
35850 
36250 
37375 
37700 
37100 
37900 
38500 
38525 

20875 
23875 
28725 
31975 
34800 
34725 
35425 
35300 
35350 
34900 
35800 
34600 



21.2 
13.3 
13.8 
10.5 
10.7 
9.5 
11.5 
10.5 

21.2 
16.8 
13.7 
10.7 
10.0 
9.0 
9.2 
8.3 
6.7 
7.5 
7.7 
6.2 

21.2 
14.0 
9.5 
8.2 
8.7 
8.0 
7.5 
7.8 
5.0 
5.7 
6.5 
5.3 



BHN 



8 

61 
66 

73 
72 
74 
72 

34 

& 
69 
70 
70 
77 
77 
80 

79 
86 
84 

34 
41 
56 
66 
72 
75 
77 
75 
77 
81 
78 
78 



*The analysis of these bars was as follows: 0.38#Cu, 0.1756*"e# 
0.08%Si, 6.88#Zn, 0.12#Ti, 0.27*Mg, 0.23*£r. 

**These test bars were placed in boiling water. The resulting 
extremely slight corrosion after long exposure probably has 
contributed to the apparent adverse aging effect under these 
conditions. 



W-3/ 



TABLE Ig 



THE TENSILE PROPERTIES OF AN Al-Zn-Mg-Cu-Cr-Ti ALLOY* 
IN SEPARATELY CAST TEST BARS AND IN HEAVY SECTIONS POURED 
FROM 1350°F AND AGED 1 YEAR AT 85°F 





Aging Treatment 


Cast^u 


Section 
Thi ckness 

iMhM - 


Y.i 
Min. 


3. 

Ave. 


T. 


S. 

Aye T 




El. 

~~ Xve. 


BHN 

Ave, 


366 


1 year at 85°F 


6-bar 


0.5 


2^600 


24750 


36000 


37600 


7.5 


8.8 


74 


step 


1.0 


22000 


22300 


26750 


30450 


2.5 


5.5 


70 






it 


2.0 


20600 


21500 


34200 


37200 


11.5 


16.2 


I* 






it 


4.0 


14550 


18600 


22500 


32900 


7.5 


16.2 


69 


365 


1 year at 85°F 


6-bar 


0.5 


25400 


25600 


38300 


39450 


8.5 


9.6 


80 


step 


1.0 


23300 


23550 


34700 


35800 


7.5 


17.7 


3 








2.0 


16850 


17900 


31700 


32900 


13.0 


14*6 








if 


4.0 


13400 


17500 


161 50 


30400 


3.5 


9.6 


68 


U3 


60 days at 85°* 


6-bar 


0.5 


19100 


19600 


35800 


36100 


12.5 


14.4 


72 




step 


1.0 


18900 


19500 


32100 


33400 


9.5 


10.5 


70 






rt 


2.0 


18500 


20100 


33100 


36600 


11.0 


15.7 


71 






ti 


4.0 


18900 


19900 


32800 


35700 


9.0 


13.9 


70 



The analyses are as follows: 



Heat 


£Cu 


Ms. 


m 




flPi 






366 
365 
U3 


0.33 
0.34 
0.27 


0.17 
0.17 
0.23 


0.08 
0.08 
0.10 


7.08 
7.02 
7.00 


0.16 
0.18 
0.18 


0.30 

0.33 
0.26 


0.26 
0.26 
0.25 



HACA 



Table 5 



TABLE V 



THE HIGH TEMPERATURE PROPERTIES OF CAST TEST BARS OF AN ALLOY 
CONTAINING 1.06# Cu, 0.16# Fe, 0»08# Si, 6.89# Zn, 0,1336 Ti, 
________ 0,26# Mg and 0.27& Cr 





Time at 








BHN* 


TemDerature 


Terms era tur e 


Y.S. 


T.S. 


#E1. 


Room 


6 months 


27800 


38400 


5.5 


82 


200 °F 


1/2 hour 




32100 


10.5 


66 


it 


3 days 




33450 


8.5 


71 


:f 


10 days 




35800 


5.0 


79 


ft 


£5 * 




37900 


4.5 


86 


it 


BO » 




37800 


3.5 


86 


ft 


100 » 




36400 


3.5 


91 


300°F 


1/2 hour 




25800 


9.5 


58 


i 1 


4 days 




29100 


6.5 


78 


if 


9 days 




27000 


8.0 


68 


it 


25 " 




23700 


8.0 


62 


it 


50 " 




22200 


9.5 


59 


if 


100 " 




20700 


8.0 


49 


400 °F 


1/2 hour 




19700 


10.5 


56 


it 


2 days 




14570 


13.5 


49 


if 


5 days 




13650 


16.5 


48 


it 


10 " 




12500 


18.5 


45 


if 


25 " 




12250 


18.0 


45 


it 


50 " 




11800 


15.5 


41 


500 °F 


1/2 hour 




11300 


23.0 


49 


if 


3 days 




8700 


33*0 


43 


q 


5 days 




8300 


20*0 


43 


ir 


10 ■ 




8550 


30.0 


41 


it 


25 " 




8050 


28.0 


43 


ii 


50 ■ 




7800 


33.0 


40 


600 °F 


1/2 hour 




6400 


29.0 


42 


it 


1 day 




6000 


41.0 


40 


ft 


5 days 




5500 


32.0 


41 


if 


10 " 




5500 


38.0 


40 


n 


15 " 




5400 


39.0 


39 


ii 


25 " 




5500 


39.0 


42 



*Brinell Hardness tests were made at room temperature , 
high temperature treatment indicated in the table. 



after the 



m 

> 

TABLE W 

THE EFFECT OF EXPOSURE TO BRAZING TIMPERATURES AND REAGDiG AT ROOM TEMPERATURE. 

TESTS MADE ON CAST TEST BARS CONTAINING 
0.38* Cu. 0.17% Fe. 0.08* Si. 6.87* Zn. 0.11* Tl. 0.26% Mg. Q.23* Cr 











Treatment 




Y.S. 


T.S. 


to. 


BfiN 












31 


days 


at 


85°F 






20300 


35600 


10.5 


66 


26 


days 


at 


85°F, 


2 hours at 900°F, ♦ 


30 days at 85°E 


19500 


33600 


9.0 


64 


1i 




it 




,. 95o°F, 


» h « it 


19500 


33450 


9./ 


63 


11 




ii 




■ " " 1000°F, " 


ii tr n it 


19500 


32700 


8.0 


67 


It 




ii 




k ., .. !050°F, " 


ii it it ii 


19600 


34650 


11.0 


68 


11 




it 




" " " 1100°F, " 


«i ti ii ii 


19900 


35800 


12.9 


67 


1t 




ii 




" " " 1120°F, « 


it ii it ii 


19300 


35200 


13.1 


66 



W-3j 



$ 40000 
cr 

CL 

cn 
CD 



X 35000 



z 

Ld 

cr 



u 
_l 

in 
z 
u 



30000 




LO 



25000L 

.2 .4 .6 .8 

PERCENT MAGNESIUM 
Figure la.- The effect of magnesium content on the tensile 

strength of alloys containing approximately 
0.4% copper, 0,15% iron, 0.08% silicon, 0.25% chromium, 
and various amounts of zinc. All alloys as cast and 
aged 30 days at 85°F. 



15 



IO 



1 




t Zn 




- 




\ \ 

V \ 


\ 3 








\&. 

\o 


V A 

Wo 




o _ 
o 






:zn 


i 


1 L_ 



O .2 .4 .6 

PERCENT MAGNESIUM 



.8 



I.O 



Figure lb.- The effect of magnesium content on the 
percent elongation in 2 inches of gage 
length of alloys containing approximately 0.4% 
copper, 0.15% iron, 0.08% silicon, 0.25% chromium, 
and various amounts of zinc. All alloys as cast 
and aged 30 days at 85°F. 



W-3/ 




PERCENT MAGNESIUM 



Figure lc- The effect of magnesium content on the 

yield strength of alloys containing 
approximately 0.4% copper, 0.15% iron, 0.08% silicon, 
0.25% chromium, and various amounts of zinc. All 
alloys as cast and aged 30 days at 85°F. 




4Q ! 1 ' I ■ I | 1 

O .2 .4 .6 .8 I.O 

PERCENT MAGNESIUM 

Figure Id.- The effect of magnesium content on the * 

Brinell hardness of alloys containing c£) 

approximately 0.4% copper, 0.15% iron, 0.08% silicon, ? 

0.25% chromium, and various amounts of zinc. All h 

alloys as cast and aged 30 days at 85°F. -° 



W-3/ 



40000 



350OO 



30000 




25000_ 

.2 .4 .6 .8 

PERCENT MAGNESIUM 

Figure 2a.- The effect of magnesium content on the 
tensile strength of alloys containing 
approximately 1.0% copper, 0.15% iron, 0.08% silicon, 
0.25% chromium, and various amounts of zinc. All 
alloys as cast and aged 30 days at 85°F. 



Ld 

x 
u 
z 

C\J 



z 

o 

o 
z 
o 

_J 
u 



z 

Ld 
U 

cr 
u 

CL 



o 


\ 

0 

\ V> 
\ \*> 

\ \ c 
\ \ 0 

\ V 


1 


1 


™ 1 

- 


.N 




} 

\ 0 




- 


J' \< 

• 

" ICXd^Zr 


• 

\ 


o\ 0 \ 

^0 \ 

B 












\ 





.6 



.8 



I.O 



O .2 .4 

PERCENT MAGNESIUM 

Figure 2b.- The effect of magnesium content on the 
percent elongation in 2 inches of gage 
length of alloys containing approximately 1.0% 
copper, 0.15% iron, 0.08% silicon, 0.25% chromium, 
and various amounts of zinc. All alloys as cast and 
aged 30 days at 85°F. 



(ft 
02 



W- 31 



H7° f — I — 1 — I — 1 — I — r 




O .2 .4 .6 .8 I.O 

PERCENT MAGNESIUM 

Figure 2c- The effect of magnesium content on the 

yield strength of alloys containing 
approximately 1.0% copper, 0.15% iron, 0.08% silicon, 
0.25% chromium, and various amounts of zinc. All 
alloys as cast and aged 30 days at 85°F. 



85 



70 



u 

? 55 



AO 



1 

- 10.9% 

< 

**> 


Zn 
f 


•X 


X • i 


x^ • 


• 


o\o/# 

°>/ 
(by oV 


X ° 

X °^ 

°X X 

X O f 


V 

o X 


X ° 


° X 


o 

// 


• X 

o>y 

V 




- 


I// 

• 


0 X 


o 




I l_ 



.2 .4 .6 .8 

PERCENT MAGNESIUM 



I.O 



Figure 2d.- The effect of magnesium content on the 

Brinell hardness of alloys containing 
approximately 1.0% copper, 0.15% iron, 0.08% silicon, 
0.25% chromium, and various amounts of zinc. All 
alloys as cast and aged 30 days at 85°F. 



W-3/ 




PER CENT MAGNESIUM PER CENT MAGNESIUM 

Figure 3a.- The effect of magnesium content on the Figure 3b.- The effect of magnesium content on the 

tensile strength of alloys containing percent elongation in 2 inches of gage J3 

approximately 1.75% copper, 0.15% iron, 0.08% silicon, length of alloys containing approximately 1.75% <g 

0.25% chromium, and various amounts of zinc. All copper, 0.15% iron, 0.08% silicon, 0.25% chromium, ? 

alloys as cast and aged 30 days at 85°F. and various amounts of zinc. All alloys as cast £ 

and aged 30 days at 85°F. • 



W-31 




PER CENT MAGNESIUM PER CENT MAGNESIUM 

Figure 3c- The effect of magnesium content on the Figure 3d.- The effect of magnesium content on the *j 

yield strength of alloys containing Brinell hardness of alloys containing & 

approximately 1.75% copper, 0.15% iron, 0.08% silicon, approximately 1.75% copper, 0.15% iron, 0.08% silicon, ? 

0.25% chromium, and various amounts of zinc. All 0.25% chromium, and various amounts of zinc. All ' oa 

alloys as cast and aged 30 days at 85°F. alloys cast and aged 30 days at 85°F. J 3 



W-3f 



^ 




















\ 

X- 










V 






0.4% C 

***** 












— - — 


I 

\ 










\ 

\ 

\ 










V 
\ 














S 




u 










- """"^ — ; 




















- 






































1.75% Cu 





40000 



35COC . 



30000 



O 2 5000 



20000 



15000 



7 9 
PER CENT ZINC 



13 



IOOOO 











— — 


TENSILE 
STRENGTH 










'EFcCENT ELON 


3ATION 












YIELD 
STRENG1 

IS 


y 

H S % 




-%yy^ 




^* BRINELL 
HARDNF* 


s 











20 



z 

cvj 
Z 

z 

O 

< 

o 
z 

o 



z 
u 

IO u 



. 5 



8O 



74 y 

D 

s 

68 r 



62 z 



56 



Figure 4.- The inside area represents the range in magnesium 

and zinc contents of cast test bars which will 
generally attain, after aging 30 days at 85<>F, a minimum tensile 
strength and elongation of 36,000 pounds per square inch, and 
10 percent respectirely . The composition represented by the 
outside dashed lines will generally produce a minimum of 
34,000 pounds per square inch and 7 percent elongation. These 
data are for aluminum alloys containing 0.15% iron, 0.08% 
silicon, 0.15% titanium, and 0.25% chromium and the copper, 
magnesium and zinc contents indicated on the chart. 



5 6 7 8 

PERCENT ZINC 

Figure 5.- The effect of zinc content on the tensile 

properties and hardness of cast test bars of 
aluminum alloys containing approximately 0.35% copper, 
0.18% iron, 0.08% silicon, 0.13% titanium, 0.28% chromium, 
and 0.27% and 0.29% magnesium. All alloys aged 30 days 
at 85°F. 




PERCENT MAGNESIUM 



Figure 6.- The effect of magnesium content on the tensile 

properties and hardness of cast test bars of 
aluminum alloys containing approximately 0.38% copper, 
0.15% iron, 6.6% zinc, 0.13% titanium, 0.22% chromium, and 
0.08, 0.19, and 0.33% silicon. All alloys aged 30 days at 
85°F. 



w- 3i 




NACA 




FIG. 8a Photomicrograph at XL 00 of an alloy contain- 
ing 1.05% Ctt, 0.15$ Fe, 0.13% Si, 7.02% Zn, 0.14% Ti, 
0,29% Mg and 0.30% Cp. Keller's etch. 




FIG. 8b Photomicrograph at X100 of an alloy contain- 
ing 0.34$ Cu, 0.17% Fe, 0.08% Si, 7.02% Zn, 0.18% Ti, 
0.33% Mg and 0.26% Cr. Keller's etch. 



mcA 



• 




FIQ. 8c Photomicrograph at X500 showing the elongated 
irregular gray constituent aAl-Fe-Si. The rounded 
light gray constituent Is C11AI2 rosettes. Unetched. 
Composition similar to that illustrated by Fig. 8b, 




FIG. 8d Same as Fig. 8c. Etched with 10* NaOH 
solution in water. The CuAlg rosettes are light 
and the aAl-Fe-Si constituent is black. 



NACA 



Figs. 9,10 




FIG. 10. The Step Casting with Gate and Risers 
Attached.