镁和钢搅拌摩擦焊接头组织分析

采用搅拌摩擦焊对镁合金(AZ31B)和钢(Q235)异种材料进行焊接,通过优化工艺参数获得最佳成形接头,并采用光学显微镜对接头显微组织进行观察,通过SEM沿板厚方向分析焊核与钢侧界面不同位置的微观形态.结果表明,镁/钢连接紧密,焊核勺子状区与镁侧分界面明显,晶粒较母材晶粒明显长大；钢侧热力影响区受机械和热的复合作用,组织不均匀,既有等轴晶组织也有条状组织,镁侧热力影响区不明显；镁热影响区晶粒粗化较钢侧严重.接头横截面钢侧显微硬度距离焊核越近硬度值越高,焊核硬度分布不均,局部区域硬度很高,最高为324.7 MPa,镁侧硬度值较均匀.

Microstructure of friction stir welded joint of magnesium and steel

Magnesium alloy (AZ31B) and steel (Q235) were friction stir butt welded. Optimal joint was obtained by adjusting the processing parameters. The microstructure of joint was observed by the optical microscope. The interfacial morphology along the thickness direction was analyzed by scanning electron microscope. The result shows that metallurgical joint of magnesium and steel is achieved. The interface between spoonshaped area of nugget and magnesium side is obvious. The grains of this part are coarse compared with that of the base material. The microstructure in the thermo-mechanically affected zone near the steel is non-uniform,composed of equiaxed grains and strip grains. The thermo-mechanically affected zone near magnesium side is inconspicuous. The grains of heat-affected zone on the magnesium side grow coarser than that on the steel side. The microhardness of local area on the steel side increases with the distance getting close to the nugget,of which the microhardness is non-uniform. In local area,hardness was very high that the maximum value is 324.7 MPa,and it is uniform on magnesium side.