镁合金电阻点焊凝固裂纹机理

Mechanism of solidification cracking of resistance spot welded magnesium alloy

关键词:  电阻点焊  镁合金  凝固裂纹

Key words:  resistance spot welding  magnesium alloy  solidification cracking

摘要:

为了获得高性能的镁合金电阻点焊接头,利用光学显微镜、扫描电镜、能谱仪研究了点焊接头裂纹的形成机理.结果表明,结晶裂纹的形成,主要与Al和Mn元素偏析造成的晶间低熔点液态薄膜,以及冷却过程中产生的拉伸应力有关.点焊参数(热输入)对熔核结晶裂纹敏感性有很大的影响.热输入增加将增大由熔核收缩引起的拉伸应力,增加原子偏析浓度进而降低液态薄膜熔点,以致于延长拉伸应力的作用时间.因此,应该选择相对低的热输入来降低点焊接头的凝固裂纹敏感性.

Abstract:

For achieving joint with high performance, mechanism of cracks in resistance spot welded magnesium alloy joint was investigated by optical microscopy,scanning electron microscope and energy dispersive spectrum,respectively. The formation of solidification cracking is caused by low melting point liquid films between dendrites due to segregation of Al and Mn atoms and tensile stress developed during cooling. Spot welding parameters (heat input) have a significant effect on susceptibility of the weld nugget to solidification cracking. The sensibility of solidification cracking increases with heat input. Because the larger heat input,the larger tensile stress caused by the shrinkage of the nugget is formed,and the lower melting point of liquid films is due to solute atom segregation with greater concentration and prolonging time for tensile stress affecting. It is favorable to select relatively low heat input for reducing sensibility of welded joint to solidification cracking.