Microstructure evolution and fracture behavior of laser welded-brazed titanium/aluminum joints with various gap sizes

In the study, the effects of gap sizes on interfacial reaction and mechanical property were investigated for laser welding-brazing of titanium alloy and aluminum alloy. The wetting width on the joint rear surface was initially increased and then decreased with the increase of gap size. A layer of Ti(Al, Si)3 with uniform thickness was primarily formed in the 0.7 mm-joint and the nanophases Ti5Si3 and Ti7Al5Si12 were dispersed in the IMC layer. The inhomogeneous sandwich structure with a continuous Ti5Si3 strip layer was detected at the Ti/Al interface of the 0.4 mm-joint. The maximum line load of the joint with 0.7 mm gap size was about 395.4 N/mm, which was 261.9 % larger than that with 0 mm gap size. The cracks preferentially initiated at Ti5Si3/Ti(Al, Si)3 interface due to their higher interplanar spacing misfit rate and then propagated inside Ti5Si3 and Ti(Al, Si)3. When the gap size was 0.7 mm, the chemical potential gradient of Si decreased by the higher peak temperature at the bottom of the joint. The continuous Ti5Si3 strip layer was inhibited because Si atoms were more evenly distributed at the Ti/Al interface. Moreover, the IMC layer of Ti(Al, Si)3 was uniform and continuous. Thus, the mechanical property was significantly enhanced.