Effect of wire feeding speed on dissimilar laser welding of NiTi shape memory alloy and 2A12 aluminum alloy

Abstract

Laser welding of NiTi shape memory alloy (SMA) and 2A12 aluminum alloy was realized by using a TC4 wire. Due to the poor metallurgical compatibility of Ti and Al elements, the surface appearance of welded joints was uneven and fluctuated. No obvious cracks were found on the surface. When the wire feeding speed increased to 280 cm/min, the pores at the interface disappeared. There were mainly a fusion zone (FZ), the NiTi SMA/FZ interface, and the 2A12 aluminum alloy/FZ interface in the welded joints. Some dendritic microstructures grew vertically toward the FZ at the NiTi SMA/FZ interface. The distance grown of the microstructure at the interface reduced while the wire feeding speed increased. Due to the increase of wire feeding speed and the decrease of the heat input per unit volume, the ability of the atoms to diffuse and migrate reduced and the trend grown of the microstructure was inhibited. For the FZ, there were α-Ti + β-Ti + Ti2Ni phases. The difficulty of decomposition for the β-Ti phase increased because the molten pool contained a large amount of the Ni elements and a small amount of Fe and V elements. After the molten pool cooled, there would be the β-Ti phase in the FZ. With the increase of wire feeding speed, the intermetallic compounds changed from Ni–Ti to Al–Ti. Besides, the fracture load of welded joints first increased and then decreased. When the wire feeding speed was 280 cm/min, the maximum fracture load of the welded joint was 176 N/mm and the fracture mode of the joint was an intergranular brittle fracture.