热处理对热轧7075铝合金组织和力学性能的影响

Effect of Heat Treatment on Microstructure and Mechanical Properties of Hot Rolled 7075 Aluminum Alloy

目的探究T6、T73和RRA热处理对不同道次压下量的热轧7075铝合金板材微观组织和力学性能的影响,确定不同道次压下量的热轧7075铝合金板材最优热处理工艺。方法分别将11%和16%道次压下量的热轧7075铝合金进行T6、T73和RRA热处理,并对热处理后的试样进行微观组织表征和力学性能测试。结果3种方式热处理后,11%道次压下量的热轧板材微观组织以拉长晶粒为主,伴随有等轴再结晶晶粒的生成,而对于16%道次压下量的热轧板材,等轴晶数量增多,故经3种方式热处理后,16%道次压下量热轧板材的屈服强度和抗拉强度均高于11%道次压下量热轧板材的相应强度。RRA热处理有效提升了16%道次压下量热轧板材的延伸率,而对于11%道次压下量热轧板材,RRA的预时效等过程会造成其晶粒粗化,从而降低延伸率,与T6和RRA热处理相比,T73热处理对力学性能的提升不显著。对于2种不同道次压下量的板材,T6热处理为最优热处理工艺。经过T6处理后,11%道次压下量的热轧板材抗拉强度达到589.8 MPa,屈服强度达到560.7 MPa,延伸率达到16.6%,16%道次压下量的热轧板材抗拉强度达到607.5 MPa、屈服强度达到580.9 MPa、延伸率达到13.6%。T6热处理后,<001>方向的织构占主导,原始板材内部存在较多的小角度晶界,热处理后大角度晶界含量增多且有静态再结晶出现。3种热处理后的拉伸试样断口形貌没有太大区别,存在大量韧窝和撕裂棱特征,说明热处理后板材塑性较好。结论热处理能调控再结晶行为,优化亚晶等微观结构,与其他7系铝合金热处理后的力学性能相比,本文的7075热轧铝合金在16%道次压下量和T6热处理条件下获得了较为优异的力学性能,说明热处理工艺设计合理。

The work aims to investigate the effects of T6,T73 and RRA heat treatment on the microstructure and mechanical properties of hot rolled 7075 aluminum alloy sheet and determine the optimal heat treatment process for hot rolled 7075 aluminum alloy sheet under different reduction per pass.The hot rolled 7075 aluminum alloy was thermally treated with T6,T73 and RRA under 11%and 16%reduction per pass,respectively.The microstructure and mechanical property of the specimen after heat treatment were characterized and tested.The microstructure of the heat-treated hot-rolled sheets was dominated by elongated grains,accompanied by the equiaxed recrystallized grains for the sheet under 11%reduction per pass.For the sheet under 16%reduction per pass,the number of equiaxial grains increased significantly,so that the YS and UTS after heat treatment were higher than those under 11%reduction per pass.The RRA heat treatment effectively improved the El under 16%reduction per pass.Processes such as pre-ageing etc.,would cause grain coarsening in the sheet under 11%reduction per pass,resulting in a decrease in El.T73 did not provide a significant improvement in mechanical properties compared to T6 and RRA heat treatments.The T6 heat treatment was the optimal heat treatment process for sheets with two different reduction per pass.After T6 heat treatment,the UTS of the hot rolled sheet under 11%reduction per pass reached 589.8 MPa,YS reached 560.7 MPa and elongation reached 16.6%.The UTS of the hot rolled sheet under 16%reduction per pass reached 607.5 MPa,YS reached 580.9 MPa,and elongation reached 13.62%.The texture in<001>direction was dominant.There were more low angle grain boundaries inside the original sheets.The content of high angle grain boundaries increased and static recrystallization appeared after heat treatment.The fracture morphology of the three heat-treated tensile specimens was similar,and the presence of a large number of dimples and tear ridge indicated excellent plasticity.Heat treatment can regulate the recrystallization and optimize the microstructure such as subgrains.Compared with the mechanical properties of other 7xxx-series aluminum alloys after heat treatment,the hot-rolled 7075 aluminum alloy under 16%reduction per pass has more excellent mechanical properties after T6 heat treatment,indicating the reasonable heat treatment process.