Microstructure and Mechanical Properties of Dissimilar TC4 Titanium Alloy/304 Stainless Steel Joint Using Copper Filler Wire
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TC4 titanium alloy was successfully welded to 304 stainless steel using gas tungsten arc welding with a CuSi3 filler wire. The Ti/weld transition zone in the joint consisted of β-Ti, Ti2Cu, AlCu2Ti, TiCu, and Ti5Si3 intermetallic compounds (IMCs) when welded with low current. As the welding current increased, more Fe dissolved into the weld pool, and massive ternary Ti-Cu-Fe and AlCu2Ti IMCs formed in the Ti/weld transition zone. The segregated Ti5Si3 phase disappeared, and complex Fe-Ti-Si-Cr IMCs formed outside the Ti/weld transition zone. The microhardness was much higher in the Ti/weld transition zone than that in the TC4 substrate and copper weld, reaching a maximum value of 619 HV. The highest tensile strength was 328 MPa when the welding current was 120 A and the traveling speed was 4 mm/s. All joints failed through the Ti/weld transition zone, and brittle cleavage features were present on the fractured surfaces. Due to the large difference in thermophysical properties between the two base metals, cracks were easily generated, which restricted the improvement in the tensile strength of the TC4/304 SS joint.
This study was financially supported by the National Natural Science Foundation of China (Nos. 51674060 and 51605075), the National Key Research and Development Program (No. 2016YFB0701401), the China Postdoctoral Science Foundation (No. 2016M601303), and Guangdong Provincial Key Laboratory of Advanced Welding Technology for Ships (Grant No. 2017B030302010). Also this study was technically supported by the Collaborative Innovation Center of Major Machine Manufacturing in Liaoning.
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