Elemental Effects on Weld Cracking Susceptibility in Al_xCoCrCu_yFeNi High-Entropy Alloy

Weld solidification and weldability of Al_xCoCrCu_yFeNi high-entropy alloys (HEA) were characterized as a function of Al and Cu molar ratio in the alloy composition. Autogenous gas tungsten arc welding (GTAW) was performed on the as-melted ingots. Fusion zone and heat-affected zone microstructures were investigated using optical and electron microscopy, and compared to thermodynamic CALPHAD-based calculations. Weld cracking susceptibility was compared to cast pin tear test (CPTT) results. It was found that strong Cu segregation on solidification promotes hot cracking in fusion welds on AlCoCrCu_yFeNi alloys (y > 0.1). Cu-rich liquid forms during the final stages of solidification and facilitates solidification cracking in the fusion zone. The Cu-rich interdendritic readily remelts during reheating and promotes liquation cracking in the heat-affected zone. The cracking mechanisms in the welds change to brittle intergranular cracking in low and no Cu alloy compositions due to a high-hardness BCC microstructure (> 500 HV). Lowering the Al molar ratio in Al_xCoCrCu_0.1FeNi alloys (x ≤ 0.5) mitigates brittle cracking by promoting FCC solidification structure.