不同热加工工艺对Al-Mg-Si-Cu合金板材力学性能和组织的影响

INFLUENCE OF DIFFERENT THERMOMECHANICAL PROCESSES ON THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF Al-Mg-Si-Cu ALLOY SHEETS

通过拉伸实验,并利用OM,SEM,TEM观察以及EBSD测试手段,研究了不同热加工工艺对Al-Mg-Si-Cu系合金板材力学性能和组织,包括织构的影响规律.结果表明,热加工工艺的变化对T4P预时效态合金的强度和应变硬化指数n基本无影响,但是对平均塑性应变比r,平面各向异性度Δr以及不同方向延伸率影响显著;热轧之后首先进行一定量的冷轧变形然后再进行退火处理获得的合金板材(工艺II)较热轧后直接进行退火处理(工艺I)获得的合金板材在固溶之后的成形性能要好,r可达0.6187,同时各向异性明显减小;虽然工艺I处理的合金板材固溶过程中PSN效应显著,但是工艺II固溶处理前的冷轧变形量和不同尺寸粒子分布情况设计合理,再结晶晶粒基本呈等轴状,且仅含有强度较低的CubeND,Cube和H织构.并根据热加工工艺对合金板材显微组织的影响规律,提出该系合金随热加工工艺进行的组织演化模型示意图.

To reduce the weight of car body, Al-Mg-Si-Cu alloys are becoming increasingly attractive as a candidate for material substitution used to produce the outer body panels of automobiles because of their favorable bake-hardening response. However, the formability still needs to be further improved compared to steels. In this work, the effect of the thermomechanical processing on the mechanical properties and microstructure of Al-Mg-Si- Cu alloy is studied through tensile test, OM, SEM and TEM observation, as well as EBSD characterization. The re- sults reveal that there is almost no change in both strengths and strain-hardening exponent n of the sheets in T4P condition after different thermomechanical processing, but the average plasticity strain ratio r^-, planar anisotropy Ar and elongations in the three directions show obvious differences. The sheet undergone hot rolling, cold rolling, intermediate annealing, cold rolling and solution （processing II） has a better formability （r^-= 0.6187） and a weaker pla- nar anisotropy than that subjected to hot rolling, intermediate annealing and then cold rolling before solution treatment （processing I）. Although the particle stimulated nucleation （PSN） effect of processing I is remarkable during solution treatment, due to the appropriate controlling cold deformation and distribution of second-phase particles with different sizes in processing II, most of the recrystallization grains are equiaxial and the recrystallization texture is only consisted of CubeND, Cube and H with a low intensity. At last, according to the relationship between the microstructure and the thermomechanical processing, the microstructure evolution model during different thermomechanical processes is established.