Crystallization control and microstructural properties of laser welded Zr_67.8Cu_24.7Al_3.43Ni_4.07 bulk metallic glasses

Laser welding was employed to weld Zr_67.8Cu_24.7Al_3.43Ni_4.07 bulk metallic glasses (BMGs). The effects of laser power and welding speed on the microstructures of different regions in the joints were studied. The crystallization control law of laser welded BMG joints is expounded, and the relationship between microstructure characteristics and hardness of as-welded joints is discussed. The results showed that the laser welding technology with high welding speed and high energy density is beneficial to maintain the amorphous structure of the molten zone in Zr_67.8Cu_24.7Al_3.43Ni_4.07 BMG joints, accompanied by some nano-grains forming. The crystallization happening in heat affected zones is severe. Laser power has a great influence on the complete penetration of as-welded joints. The degree of crystallization in heat affected zones can be effectively controlled through lowering laser power or increasing the welding speed to reduce heat input. Vickers hardness tests reveal that the hardness of the molten zones of the welded joint is slightly higher than that of base material, and the hardness of heat affected zones is significantly lower than that of the base material.