Effect of Solutionizing and Aging on Microstructure and Mechanical Properties of Warm-rolled 7075 Alloy

The effect of solution and aging treatments on microstructure and mechanical properties of warm-rolled 7075 alloy was investigated via optical microscope, electron backscattered diffraction, transmission electron microscopy and tensile tests. The 7075 alloy was subjected to solution treatments at 450 ℃ for 1 h(ST1),490 ℃ for 1 h(ST2) and 1.5 h(ST3). Three aging routes were carried out on samples from ST2: one-step(A1),two-step(A2), and three-step aging(A3). The experimental results show mainly recrystallized equiaxed grains in ST1 and ST3 state but a combination of elongated and equiaxed grains in ST2 condition. Three aged alloys have similar microstructures of sample ST2 while the recrystallization frequency gets decreased after aging.The least recrystallization fraction occurs in A2 state. Three aged 7075 alloys all possess enhanced strength and plasticity. Precipitates characterization reveals the maximum strength is achieved in A2 sample as the matrix precipitates are composed mainly of small η and many η′ phases. Aging route A2 appears preferable to other two aging conditions for attaining a pretty excellent combination of strength and plasticity.