Development of high strength wrought aluminum-base alloys
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In the p r e s e n t w o r k , a l l o y s g e n e r a l l y s i m i l a r to those of the f o r e g o i n g i n v e s t i g a t i o n s w e r e studied. The g e n e r a l a i m s w e r e to 1) d ev el o p a s i m p l e s m a l l s c a l e t e s t f o r alloy d e v e l o p m e n t of n o n f e r r o u s a l l o y s , 2) e x a m i n e w h e t h e r o r not the powder m e t a l l u r g y m e t h o d of f a b r i c a t i n g a l u m i n u m al l o y ingots is inh e r e n t l y able to p r o d u ce s t r o n g e r a l l o y s than m o r e conventional ingot c a s t i n g t e c h n i q u e s , and 3) d e t e r m i n e s o m e suitable c o m p o s i t i o n s and t r e a t m e n t f or high s t r e n g t h a l l o y s of the A I - Z n - M g - C u f a m i l y , b e ginning f r o m a c a s t ingot.
EXPERIMENTAL PROCEDURE Alloy Selection. The basic guidelines for choosing alloys for study were that these alloys should i) be generally of the AI-Zn-Mg-Cu family, 2) contain larger amounts of one or more solutes than does 7075 alloy, and 3) be completely, or nearly completely, solutionizable. The selection of alloy composition was done with a study of appropriate phase diagrams, e.g., the quaternary of Strawbridge et al. 8 and the ternaries of Little et a l f l ,~~ and with the aid of previous work cited above. Approximately thirty-five such alloys were initially chosen for study. Of these, thirty were found to be completely solutionizable (or sufficiently so to warrant further study). These were then processed and tested. Selected results from nine of the alloys studied are presented and discussed herein. Table I lists these alloys, in order of increasing zinc content, and shows also the thermomechanical proc-
Table I. Composition and Solution Temperature of Alloys Studied
Composition, wt pct
Alloy Designation
Zn
Mg
Cu
Cr
1 2 3 4 5 6 7 8 9
7.3 7.7 8.1 8.1 9.0 9.5 9.9 10.0 13.0
3.2 2.5 2.5 3.2 3.2 2.8 3.1 3.8 2.0
2.0 1.6 1.6 1.0 1.0 2.0 1.0 0.75 2.0
0.25 0.20 0.20 0.18 0.18 0.18 0.18 0.18 0.18
Mn
Ti
0.18 0.15 0.15 0.18 0.15 0.18 0.15 -
SolutionTemperature, ~ 890* 875 890 900 900 800* 900 875 to 890* 875*
*Alloysin whicha smallamount(lessthan 0.5 vol pct) secondphase remained after solution treatment.
VOLUME 1, JANUARY 1970-191
essing employed to obtain the properties which are r e p o r t e d i n T a b l e II. Fig. 1 shows the alloy compositions superimposed on three isothermal sections (860~ from the A1Zn-Mg-Cu quaternary phase diagram. Most of the all o y s l i e o u t s i d e t h e c~ s o l i d s o l u t i o n r e g i o n a t 8 6 0 ~ but many were completely solutionizable at the solution temperatures employed. Guides used to aid in selecting suitable compositions and treatments included work of other investigators, metallographic structures, and phase diagrams, as noted above. In addition, hardness measurements were used as a rough guide of yield and tensile s t r e n g t h s to b e e x p e c t e d f r o m a g i v e n t r e a t m e n t . Fig. 2 shows the fair correlation obtained. Note that there is con
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