Microstructure and mechanical properties of laser beam welded TC4/TA15 dissimilar joints

The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloys were investigated. The results showed that the coarse columnar grains containing a large amount of acicular α and martensite α′ were present in the fusion zone (FZ), some residual α phases and martensite structure were formed in the heat-affected zone (HAZ) on TC4 side, and bulk equiaxed α phase of the HAZ was on TA15 side. An asymmetrical microhardness profile across the dissimilar joint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM. The orders of yield strength and ultimate tensile strength were as follows: TC4 BM > TC4/TC4 similar joint > TA15 BM > TA15/TA15 similar joint > TC4/TA15 dissimilar joint, and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from 1×10−4 s−1 to 1×10−2 s−1. The TC4/TA15 dissimilar joints failed in the TA15 BM, and had characteristics of ductile fracture at different strain rates.