压铸镁合金AZ91D搅拌摩擦焊接头焊核演变机理研究

Evolution Mechanism of Weld Nugget Zone of FSW Joint of Die Casting AZ91D Magnesium Alloy

搅拌针旋转频率为1200r/min、焊接速率为40mm/min条件下,对4mm厚的压铸镁合金AZ91D进行连接,可获得无缺陷的焊缝接头。使用OM,SEM对焊缝接头微观组织进行观察。结果表明:压铸镁合金AZ91D搅拌摩擦焊接头焊核区域微观组织呈现出较大差异,顶部冠状区组织为均匀粗大、高致密度的再结晶晶粒,平均晶粒约为15μm;中心环形区域及焊核底部组织相对细小,均匀程度不如焊核冠状区;焊核区组织均为再结晶晶粒,晶粒形核模式与非连续动态再结晶模式类似。

Die casting plates of AZ91D magnesium alloy with thickness of 4mm, were welded by friction stir welding at the rotating speed of 1200r/rain and the welding speed of 40mm/min. The weld joint with no defect can be obtained. The joint microstructures were observed by OM,SEM. The results show that the microstructures are distinctly different in weld nugget zone. The grains of crown zone at the top of weld nugget are uniform, coarse and highly dense recrystallized grains with an average grain size 15μm;the grains of the central ring area and bottom zone are relatively fine and recrys- tallized and less uniform than that of the crown zone. The microstructures of weld nugget are recrystallization grain. The grain nucleation model are similar to the discontinuous dynamic recrystallization mechanism.