镁/钢异种材料点焊接头力学性能及显微组织分析

采用三相次级整流电阻焊机进行镁/钢异种材料电阻点焊,研究并确定了工艺参数范围和最佳数值.通过金相显微镜观察了接头的显微组织特征,并采用显微硬度计测试了接头各区域的显微硬度.结果表明,接头的剪切力随着焊接时间(2 ～ 14周波)、焊接电流(20～ 37.5 kA)以及电极力(5～8 kN)的增大均呈先增大后减小的趋势.当焊接时间8周波、焊接电流32 kA、电极力7 kN时,最大接头剪切力达6.961 kN,形成纽扣断裂.接头由半椭圆形镁合金熔核和钢侧热影响区组成,镁侧熔核显微组织由柱状晶和等轴晶组成,钢侧热影响区显微组织为板条状马氏体.镁侧离熔合线越近硬度越高,而钢侧最高硬度出现在钢板的中心.

Analysis of microstructure and mechanical properties of dissimilar metal spot welded joint between magnesium alloy and steel

Three-phase secondary rectification spot welding machine was used to conduct dissimilar metal joining of magnesium alloy to steel,and the window of welding parameters and optimum parameters were obtained.The microstructure of the joints was examined with optical microscope and the microhardness in different zones was measured.The results show that the shearing strength increased initially and then decreased with the increase of welding time T (2-14 cycle),welding current I (20-37.5 kA) and electrode pressure P (5-8 kN).The maximum shearing strength reached 6.961 kN when T was 8 cycle, I was 32 kA,and P was 7 kN.The joint was composed of nugget on magnesium alloy side,with equiaxed grains and columnar grains,and heat-affected zone on steel side,with lath martensite.On magnesium side,the closer distance of measured point to the fusion line,the higher the hardness was.The highest hardness appeared in the center of steel sheet on steel side.