激光焊接过程中残留液体金属的高速高倍在线观察

来源期刊：金属学报2011年第3期

论文作者：温鹏 获崎贤二 山本元道

文章页码：305 - 310

关键词：激光焊接； 凝固热裂纹； 残留液体金属； 在线观察； 急冷

Key words：laser welding； solidification cracking； residual liquid metal； in situ observation； quenching

摘    要：采用高速摄像机和光学显微镜构成的摄像装置对激光焊接熔池后端的凝固行为进行高速高倍摄像,详细记录了柱状晶从液态熔池后部析出过程以及残留在已析出柱状晶周围的液体金属的凝固行为.采用液体Sn急冷将焊接过程中正在凝固的焊缝金属冷冻保存到室温,并与高速高倍摄像观察到的熔池后端的凝固行为进行了对比分析.对3种奥氏体不锈钢材料焊缝凝固过程中残留液体金属的存在范围进行了观察和比较.在线观察到的残留液体金属是焊缝金属凝固过程中固/液相共存区间的初始部分,即与熔池相连的较多的液体金属.针对3种不锈钢材料在线观察到的残留液体金属的存在范围与热裂纹实验获得的热裂纹敏感性有较好的对应关系,为发展一种通过在线观察判断材料凝固热裂纹敏感性的方法提供了实验依据.

Abstract: Weld solidification cracking is resulted from the low ductility during solidification progress of weld metal,which is considered to be determined by the distribution of residual liquid metal at solidification front.Thus,the in situ observation of residual liquid metal during welding can give significant information of solidification progress and weld solidification cracking.Few reports have been found so far in this aspect though many in situ observation researches have been carried out in welding field,for example,the observation of droplet transfer,weld pool shape,weld plasma and phase transformation etc..In this paper,solidification behavior of residual liquid metal at the trailing edge of the weld molten pool was in situ observed directly during laser welding by using high speed camera and high magnification optical lens.The precipitation of columnar grain from the molten pool and the solidification of the residual liquid metal at the trailing edge of weld molten pool were recorded in detail by using the high speed video system.Meanwhile,the solidifying structures in solidification process were frozen and reserved to room temperature by using the liquid Sn quenching method during laser welding.The quantity and morphology of residual liquid metal in quenched samples were observed and compared with the in situ observation results.It was found that the in situ observed residual liquid metal was the initial part of the coexistence range of liquid and solid during solidification progress. The in situ observed existence range of residual liquid metal has correspondence with the solidification cracking susceptibility in accordance with the fan-shaped hot cracking test results for three different austenite stainless steels.Consequently,this research provides experimental basis for the relationship between residual liquid metal and solidification cracking susceptibility.It shows the possibility to develop an in situ observation method to directly evaluate solidification cracking susceptibility of different materials during welding process.