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

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.