Consider the aluminum end of the aluminum=copper phase diagram in the figure accompanying this problem. (a) Outline the complete program for obtaining a maximum hardness in an alloy of aluminum, with 4 percent copper, if the aging temperature is 403 K. (b) When the maximum hardness is obtained, what would be the nature of the precipitate? Explain.
Solution:
(a) The first step would be to give the metal a solution treatment which involves heating and holding it at a temperature in the ? phase region. The temperature of the treatment would probably be around 520 to 530°C. It should be held there long enough to form a homogeneous solid solution. The second step is a quench down to ambient temperatures. This produced a highly supersaturated specimen. The last step is the aging treatment at 403 K or 130°C. The specimen would have to be held at this temperature for about 60 to 70 days, as may be seen in Fig. 16.10.
(b) Figure 16.10 also indicates that the microstructure at the end of this aging treatment would consist of alpha phase aluminum crystals containing a fine precipitate composed of both , Ø and Ø particles.
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