The effect of pre-aging on stress aging behavior and mechanical properties of 7B50 aluminum alloy
The microstructure of 7B50 aluminum alloy after pre-aging and creep aging was observed by scanning electron microscopy and transmission electron microscopy.The creep aging test was carried out by electronic creep testing machine.The mechanical properties of the alloy were tested by tensile machine.The effect of pre-aging on the microstructure and mechanical properties of creep aging aluminum alloy was analyzed.The research result shows that with a pre-aging temperature of 140℃3 h and creep aging 8 h at 160℃160 MPa,the mechanical properties of the samples are significantly enhanced with yield strength of 593.4 MPa,making it a highly promising sheet material for future creep-ageing forming.Pre-aging can decrease the creep strain(compared to the room-temperature sample after solution treat-ment)by reducing the vacancy concentration.The pre-aging can also manipulate the lattice distortion and creep strain by promoting the atom diffusion.In addition,the increase of pre-aging temperature can decrease vacancy concentration and thus inhibit the phase transforma-tion from η′ to η.This results in a desirable microstructure composed of high-density and dispersed η′phases,significantly improving the strength of the alloy.At the same time,the pre-aging produces a"peak aging region"during creep-aging,which is beneficial to prolong the aging time and improve the creep behavior without sacrificing the strength.
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