拉压应力下7B50铝合金应力松弛时效行为研究

Stress relaxation aging behavior of 7B50 aluminum alloy under tensile and compressive stress

通过应力松弛实验、力学性能测试和透射电子显微镜组织观察并研究了不同初始应力水平和温度条件下7B50铝合金的拉伸和压缩应力松弛、时效析出及其强化行为。结果表明:拉伸和压缩应力松弛时效行为存在不对称性,前期拉应力松弛速率大于压应力松弛速率,但拉应力松弛速率下降较快;后期的拉应力松弛速率小于压应力松弛速率,使得两者应力松弛曲线出现交叉点。随着初始应力水平和时效温度的提高,拉伸和压缩应力松弛量均增加,应力松弛曲线交叉时间提前。相比拉应力松弛时效后的合金,压缩应力下合金的析出相略细小弥散,晶界无析出带更窄。因此,应力松弛时效后压应力下合金的屈服强度和抗拉强度均优于相同条件拉伸应力下的合金。

The tensile and compressive stress relaxation,aging precipitation and strengthening behavior of 7 B50 aluminum alloy at different initial stress levels and temperatures were studied by stress relaxation experiment,mechanical properties test and transmission electron microscope(TEM)observation.The results show that there is asymmetry between tensile and compressive stress relaxation aging behavior,the tensile stress relaxation rate is faster than the compressive stress relaxation rate in the early stage,but the tensile stress relaxation rate decreases rapidly;the tensile stress relaxation rate is lower than the compressive stress relaxation rate in the later stage,which makes the cross points of the two stress relaxation curves.With the increase of initial stress level and aging temperature,the amounts of both in tensile and compressive stress relaxation increase,and the cross time of stress relaxation curve is advanced.Compared with the alloy after tensile stress relaxation aging,the precipitates in the alloy under compressive stress are slightly smaller and dispersed,and the grain boundary free zone is narrower.Therefore,the yield strength and tensile strength of the alloy under compressive stress after stress relaxation aging are better than those under tensile stress with the same condition.