Interfaces bonding mechanism in coaxial dual-beam laser welding-brazing of Ti alloy and steel joint with Mg-Gd-Y-Zr alloy filler

Coaxial dual-beam laser welding technology and Mg-Gd-Y-Zr alloy as filling material were used to obtain TC4 titanium alloy and QP980 steel lap joint. And the maximum tensile load of the joint reached 3000 N/cm. Bonding mechanism of Mg/steel interface and Mg/Ti interface was mainly studied. Gd and Y elements would form compounds with Mg and Fe, respectively. It was found that at the Mg/steel interface, the lattices of two compound were connected by sharing Gd and Y atoms, where the BCC structured Mg24(Gd, Y)5 compound act as the heterogeneous nucleation core of α-Mg. At the Mg/Ti interface, Zr, Y and Gd atoms diffused into Ti and formed a diffusion layer with thickness of 35 nm. Atoms diffusion helped mismatch between the (100)BCC of β-Ti and the (101¯0)HCP of α-Mg reduce from 15.95% to 0.25%, thus realizing the joining of the Mg/Ti interface.