镁合金焊接凝固裂纹敏感性评价及晶间液相回填规律分析

Evaluating solidification cracking susceptibility of Mg alloys and intergranular liquid backfilling during welding

试验选用ZK61,AZ31,AZ61和AZ91镁合金进行焊接凝固裂纹敏感性的分析.首先进行了双速模式下的横向移动裂纹敏感性试验,获得了4种镁合金的临界横向移动速度,并对凝固裂纹敏感性进行了评估和排序:ZK61>AZ31>AZ61>AZ91,与单速模式试验结果以及基于│dT/d(f_(S))^(1/2)|_(max)作为裂纹敏感指数得到的计算预测结果一致,验证了双速模式的横向移动裂纹敏感性试验用于评估镁合金凝固裂纹敏感性的有效性.凝固裂纹尖端及周边存在液相回填特征,ZK61镁合金的晶间回填液相呈非连续状且回填通道较窄,难以起到愈合裂纹效果,增大了凝固裂纹敏感性;AZ91镁合金液相回填通道宽度最大,有利于晶间液相回填,降低了凝固裂纹敏感性.

In present work,the widely used Mg alloys ZK61,AZ31,AZ61 and AZ91 were selected for investigating the solidification cracking susceptibility during welding.Transverse motion weldability(TMW)test in two-speed mode was used to evaluate the susceptibility of Mg alloys to solidification cracking during welding.The critical transverse moving speed was obtained and considered as an index to estimate the solidification cracking susceptibility of Mg alloys as ranking:ZK61>AZ31>AZ61>AZ91.The ranking is consistent with the results of one-speed test and predicted results based on│dT/d(f_(S))^(1/2)|_(max).It was shown that two-speed test of TMW is effective to evaluate the susceptibility of Mg alloys to solidification cracking.According to the backfilled liquid at the tip of or near the solidification cracking,the intergranular backfilled liquid of ZK61 is discontinuous and the channel is narrow,which is difficult to heal the crack and increases the solidification cracking susceptibility.The liquid backfilling channel of AZ91 is the widest,which is conducive to intergranular liquid backfilling and reduces the solidification crack susceptibility.