Microstructure and mechanical property of gas tungsten arc and friction stir welds of L12 precipitate FCC high-entropy alloy

Abstract

The welding technology is significant for application of high-entropy alloys (HEAs) in the industry. In this study, the mechanical properties and microstructures of Al0.2Co1.5CrFeNi1.5Ti0.3 after welding by gas tungsten arc (GTA) welding and friction stir welding (FSW) are discussed, respectively. GTA welding of precipitated HEAs resulted in the formation of dendrites in the fusion zone; the hardness and tensile strength of the GTA weld decreased to 68% and 51% compared to the base metal, respectively. However, FSW exhibited excellent mechanical properties, which were still over 94% of the hardness value and tensile strength of the base metal. The microstructure was characterized by discontinuous dynamic recrystallization and the grain refinement effect in the stir zone. The microstructure of the two welds resulted in different mechanical properties. The weld after FSW was strengthened by the grain refinement strengthening, which almost compensates the decrease in hardness caused by the re-dissolution of all precipitates in the stir zone, while the dendritic structure strongly affected the mechanical properties and softened the fusion zone after the GTA process. During the tensile test, the digital image correlation was conducted simultaneously. It shows that the GTA weld had lower strength with nonuniform deformation in the fusion zone, while the FSW weld showed higher strength with uniform deformation.