Study on interfacial characteristics and properties of NiTi/Al–Mg joint by vaporizing foil actuator welding

As a new type of impact welding technology, Vaporizing Foil Actuator Welding (VFAW) has the advantages of high welding efficiency and small heat affected zone, which could avoid the decline of shape memory properties of the NiTi alloy in the NiTi/metals joint of fusion welding. Therefore, NiTi/Al–Mg VFAW experiments under different discharge voltages and standoffs were carried out to analyze the effects of process parameters on interface morphology, mechanical and functional properties. The results showed that high strength welding between NiTi and Al–Mg alloys were realized. With the increase of discharge voltage and standoff, the interface morphology changed to flat, a small amount of melting layer, wave, continuous melting layer, and the joint performance increased first and then decreased. The difference in properties between NiTi and Al–Mg alloys led to the change of microstructure and nano-hardness at the interface. Equiaxed recrystallized grains and small slender grains appeared on Al–Mg and NiTi alloy respectively. The nano-hardness of both sides increased, but the hardening range of the Al–Mg alloy side was smaller. The changes of phase transformation temperatures of the NiTi/Al–Mg joints were small compared to NiTi base, indicating the VFAWed NiTi alloy still maintained the original shape memory function. This work deepens the understanding about the properties of NiTi/Al–Mg VFAW, and is helpful for expanding the application of NiTi shape memory alloy.