HARDENING RESPONSE TO RAPID AGING PROCESSES AND PRECIPITATION IN Al-7%Si-0.3%Mg ALLOY

An orthogonal test was designed to obtain a optimized rapid aging process in order to shorten aging time. Hardness and tensile tests and TEM observation were used to evaluate the hardening response to the rapid aging process. An optimized rapid aging process, 160 degrees C2h+200 degrees C2h, is obtained. Under this process, the alloy has an approximately equal hardness and strength to the conventional single stage peak aging process, but the aging time of the rapid aging process is remarkably shortened, only 16.7% of the conventional process. Compared with the conventional aging process, the number density of beta '' precipitates formed during the rapid aging course is reduced, however, the amount of beta' precipitates is remarkably increased. Though the contribution of the beta '' precipitates to hardening is reduced, that of the high density of beta' rod precipitates is considerably increased, thus the rapid aging process produces an approximately equal hardening effect to the conventional peak aging process.