Abstract
The effect of elastic tensile stress on the microstructure of 7075 aluminum alloy aged at 433K for 1h has been investigated in this paper. It was found that double peaks occur in hardness after various aging treatments. The peak microhardness of the stress-aged specimens reaches 178HV, much higher than that of the conventional aged sample. The stress aging exhibits a diverse microstructure: the GPII zones and various sizes of η precipitates are just identified in the stress-free aged sample; the main hardening η′ precipitates, with the highest and lowest degree of dispersion, are formed after 25 and 50MPa stress-aged respectively; a finer aging precipitate size distribution, a larger grain boundary precipitate size and spacing and a wider precipitate free zone are represented in the stress-aged specimens. After the 25MPa stress aging treatment, a preferential growth orientation of the larger-size MgZn2 phase is observed in 7075 aluminum alloy. During aging, the external stress accelerates the growing of the larger-size MgZn2 phase, promotes the formation of the η′ precipitate and inhibits the formation of the η phase. Our study provides a new process to improve the comprehensive properties of Al–Zn–Mg–Cu alloys.
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