热影响区连续孔隙状裂纹的表征及产生机理

Characterization and formation mechanisms of continuous porosities-like cracks in the heat-affected zone

关键词:  焊接缺陷  热影响区  液化裂纹  部分熔化区  热裂纹

Key words:  weld defect  heat-affected zone  liquation cracking  partially melted zone  hot cracks

摘要:

以凝固温度范围极宽的合金为对象，研究焊接热影响区的液化现象，表征该区域中出现的连续孔隙状裂纹，并分析其产生机理. 结果表明，连续孔隙状裂纹的产生与母材中残余第二相颗粒的连续分布、热影响区中出现的严重液化现象及液相的流失密切相关. 其产生机理在于：焊接加热时，第二相颗粒加剧了晶界液化的程度，并形成连接热影响区和焊接熔池的液相通道；冷却过程中，由于熔池区熔体体积收缩促使热影响区中的液相流向熔池；凝固末期，通道因胞状晶生长而被堵塞，导致液相无法从熔池回填，从而在热影响区形成连续孔隙状裂纹.

Abstract:

The alloy with extreme wide solidification temperature range was employed to investigate liquation phenomenon in the heat-affected zone (HAZ) of welded joint. The continuous porosities-like liquation cracks were characterized and their formation mechanisms were analyzed and discussed in details. The results show that the occurrence of continuous porosities-like liquation cracking is closely related to the continuously distributed residual particles of second phase in the base metal, seriously constitutional liquation of the HAZ and the loss of liquid phase in it. The formation mechanisms demonstrated that as the heat source approaching the residual particles of second phase melted, which prompted the extent of liquation along the grain boundaries in the HAZ, and the liquid exchange channels were built between the fusion zone and HAZ. As the heat source leaving, the liquid in HAZ was sucked into the fusion zone under the force produced by cooling shrinkage of the molten metal in fusion zone. At the final stage of solidification, the porosities-like liquation cracks were formed due to the absence of liquid caused by blocking of the channels for liquid filling back from the fusion zone.