Microstructure and mechanical properties of TC4/QP980 laser-arc hybrid welded lap joint with CuSi3 filler wire: Experiment and first-principles calculation

Intermetallic compounds (IMCs) play a crucial role in impeding the improvement of the quality of titanium alloy and steel welded joint. In this study, the influence of heat input on the microstructure, mechanical properties and fracture mode of TC4 titanium alloy and QP980 high-strength steel laser-arc hybrid welded lap joint with CuSi3 filler wire was studied. Moreover, the microstructure evolution mechanism and fracture mechanism of the welded joint were explored through experimental and computational methods. With the increase of heat input, the shear tensile force of the welded joint initially exhibited an increasing trend followed by a subsequent decline, peaking at 3690 N/cm when a TIG current of 120 A was employed. The weak section of the welded joint changed from the Ti/Cu reaction zone to the fusion zone with increasing the heat input. Computational results showed that the large brittleness of TiFe2Si and the low interfacial separation work of α-Cu(111)/TiFe2Si(220) interface were key factors contributing to the poor mechanical properties of joints with high heat input.