Effects of Laser Welding Parameters on Microstructure and Mechanical Properties of Laser Welded TiNi Shape Memory Alloy (SMA) Wires

The microstructures and mechanical properties of laser welded TiNi alloy wire joints have been investigated by changing the laser welding parameters (input energy and pulse duration). The results showed that the welded joints had a needle-like grain structure and consisted of 132 and B19' mixed phases. The input enemy and pulse duration have great effects on the joint quality. The proper combinations of input energy and pulse duration favour improving the tensile strength of the joints. The maximum joint strength (367 MPa) was achieved using the input enemy of 7.07 J and the pulse duration of 10 ms, reaching only about 35% of the base metal (BM) strength (1030 MPa). The joint fracture all occurred in the fusion zone, instead of the heat affected zone (HAZ) with a coarse grain structure. The reason for low joint strength was discussed in this investigation.