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 alpha-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 beta-Ti and the (1010)HCP of alpha-Mg reduce from 15.95% to 0.25%, thus realizing the joining of the Mg/Ti interface.

Automated summary

Coaxial dual-beam laser welding technology and Mg-Gd-Y-Zr alloy were utilized to achieve a lap joint of TC4 titanium alloy and QP980 steel, with a maximum tensile load of 3000 N/cm. The bonding mechanism of the Mg/steel interface and Mg/Ti interface was investigated. It was found that compounds formed between Mg and Gd, as well as Y and Fe, at the respective interfaces. The Mg/steel interface exhibited a connection between the lattices of the two compounds through shared Gd and Y atoms, with BCC-structured Mg24(Gd, Y)5 compound acting as the heterogeneous nucleation core of alpha-Mg. At the Mg/Ti interface, diffusion of Zr, Y, and Gd atoms into Ti formed a 35 nm thick diffusion layer, reducing the mismatch between the (100)BCC of beta-Ti and the (1010)HCP of alpha-Mg from 15.95% to 0.25%, enabling the joining of the Mg/Ti interface.