The Mg–Zn–Zr–Gd alloys belong to a group of biometallic alloys suitable for bone substitution. While biocompatibility arises from the harmlessness of the metals, the biocorrosion behavior and its origins remain elusive. Here, aiming for the tailored biodegradability, we prepared the Mg–2.0Zn–0.5Zr–xGd (wt %) alloys with different Gd percentages (x = 0, 1, 2, 3, 4, 5), and studied their microstructures and biocorrosion behavior. Results showed that adding a moderate amount of Gd into Mg–2.0Zn–0.5Zr alloys will refine and homogenize α-Mg grains, change the morphology and distribution of (Mg, Zn)₃Gd, and lead to enhancement of mechanical properties and anticorrosive performance. At the optimized content of 3.0%, the fishbone-shaped network, ellipsoidal, and rod-like (Mg, Zn)₃Gd phase turns up, along with the 14H-type long period stacking ordered (14H-LPSO) structures decorated with nanoscale rod-like (Mg, Zn)₃Gd phases. The 14H-LPSO structure only exists when x ≥ 3.0, and its content increases with the Gd content. The Mg–2.0Zn–0.5Zr–3.0Gd alloy possesses a better ultimate tensile strength of 204 ± 3 MPa, yield strength of 155 ± 3 MPa, and elongation of 10.6 ± 0.6%. Corrosion tests verified that the Mg–2.0Zn–0.5Zr–3.0Gd alloy possesses the best corrosion resistance and uniform corrosion mode. The microstructure impacts on the corrosion resistance were also studied.

In this study, an upper sheet of an A6061 aluminum alloy and a lower sheet of Q235 steel were welded by resistance element welding with a steel rivet. The temperature field during welding was calculated using ABAQUS numerical simulation software, and the interfacial microstructure was observed. A nugget was formed between the rivet shank and the lower sheet. With increases in welding current and welding time, the tensile shear load of the joint increased first and then decreased slightly. When the welding current was 14 kA and the welding time was 300 ms, the tensile shear load of the joint reached a maximum of 7.93 kN. The smaller the distance from the position to the lower sheet along the interface between the rivet shank and upper sheet, the longer the high-temperature duration and the higher the peak temperature during welding. At the junction of the rivet shank, upper sheet, and lower sheet in the joint, the high-temperature duration was the longest, at about 392 ms, and the peak temperature was the highest, at about 1237 °C. The results show that the smaller the distance from the position to the lower sheet along the interface between the rivet shank and the upper sheet in the joint, the thicker the reaction layer generated there, and that the thickness of the reaction layer was about 2.0 μm at the junction of the rivet shank, upper sheet, and lower sheet in the joint.