初始晶粒尺寸对高温交叉轧制镁合金板材组织和力学性能的影响

目的 揭示晶粒尺寸对多道次高温交叉轧制AZ31镁合金板材组织和力学性能的影响规律及机制.方法 通过对不同初始晶粒尺寸的镁合金板材进行高温交叉轧制变形及热处理,获得不同状态的镁合金板材,采用金相显微分析、X射线衍射(XRD)分析及室温拉伸实验等手段研究镁合金板材的晶粒组织(形态、尺寸、取向)及力学性能.结果 经过多道次交叉轧制后,不同初始晶粒尺寸的板材均发生了孪生现象,但粗晶板材的晶粒尺寸仍明显大于细晶板材.退火处理后,细晶退火态板材组织均匀性较好,而粗晶退火态板材的组织虽有细化,但并不均匀.随着交叉轧制次数的增加,两种板材内非基面取向晶粒都有所增加.退火后粗晶板材中非基面取向晶粒更多.结论 晶粒细化和晶粒取向强化导致退火后的交叉轧制细晶镁合金板材具有更高的强度.粗晶板材伸长率较高主要与其具有更多的非基面取向晶粒有关.

Effect of Initial Grain Size on Microstructures and Mechanical Properties of Magnesium Alloy Sheets Processed by Cross Rolling at High Temperature

The effect rule and mechanism of grain size on microstructure and mechanical properties of AZ31 magnesium alloy sheet by cross rolling at high temperature were revealed. Magnesium alloy sheets with different initial grain sizes were obtained by cross rolling deformation at high temperature and heat treatment. Grain structure (morphology, size, orientation) and mechanical properties of magnesium alloy sheets are studied by means of metallographic analysis, X-ray diffraction (XRD) analysis as well as tensile test at room temperature. After multi-pass cross rolling, twinning phenomenon can be observed in the sheets with different initial grain size, but the grain size of coarse grain sheet is obviously larger than that of fine grain sheet. After annealing, microstructures of the fine grain sheet are relatively uniform, and that of the coarse grain sheet are more refinement but nonuniform significantly. With the increase in cross rolling times, the grains with non-base plane orientation increase in the two kinds of sheets, and more grains with non-base plane orientation are present in the coarse grain sheet after annealing., The annealed fine grain sheet exhibits higher strength after cross rolling because of grain refinement and grain orientation strengthening. The higher elongation of coarse-grained sheet might be mainly related to the fact that there are more non-basal oriented grains.