两步升温热轧工艺对AZ31镁合金薄板各向异性及成形性能影响

Effect of two-step increased temperature thermal rollingon anisotropy and stretch formability of AZ31 magnesium alloy sheets

采用两步梯度升温轧制工艺对AZ31镁合金板材进行轧制,探究轧制过程对镁合金板材显微组织织演化、各向异性及成形性能的影响。第I步轧制在300℃开展,其每道次压下量为15%;第II步轧制在550℃进行,其每道次压下量为40%。经过共4道次轧制后,最终获得厚度为1 mm的镁合金薄板。结果显示,第I步低温轧制过程不更换轧制方向时,试样中生成大量剪切带;而更换轧制方向时,组织内部主要为孪晶和再结晶晶粒。随着II步轧制温度的升高,由于动态再结晶急剧激发,剪切带数量及尺寸逐渐减小,晶粒明显细化。根据IGMA分析得出,非基面滑移,特别是棱柱面滑移活动增强。轧制退火后的AZ31镁合金薄板的力学性能得到提高,各向异性减小,冲压成形性能得到明显改善。

The effect of a two-step gradient thermal rolling process on the microstructure evolution and anisotropy as well as the stretch formability of AZ31 magnesium alloys was investigated.Step I was carried out at 300°C with a small rolling reduction of 15%per pass,while the rolling temperature of Step II was 550°C with per pass reduction of 40%.Finally,Mg alloy sheets with a thickness of 1 mm were achieved after total four rolling passes.The results indicate that shear bands are generated in rolled samples when the rolling direction is unchanged,while twinning lamellae and recrystallized grains emerge in samples when the rolling direction is changed in Step I.After Step II rolling,the size and amount of shear bands decrease,and grains are refined greatly owing to the enhanced activation of dynamic recrystallization.Besides,non-basal slips,especially prismaticáañslips,are found to be promoted as well based on the in-grain misorientation axis(IGMA)analysis.Therefore,improved mechanical properties,reduced anisotropy,and the improvement of stretch formability of AZ31 Mg alloy sheets are achieved.