Effect of rare earth elements on microstructure and mechanical properties of new Al-Mg alloy welded joints

Effects of Sc and Zr elements on microstructure and mechanical properties of new Al-Mg alloy welded joints were studied. A two-dimensional numerical analysis model of MIG arc was established to simulate distribution of arc temperature field. The maximum temperature of arc exceeded 20 000 K and temperature distribution had a large temperature gradient, which showed that high temperature arc had a certain effect on burning loss of beneficial elements of the alloy. ER5356, ER5B06 and ER5B71 welding wires with different alloying elements were used as filler materials, MIG welding experiments were carried out on new Al-Mg alloy with 2 mm thickness to study effects of high Mg welding wires with adding different rare earth elements on welding performance and microstructure. The results showed that welded joints with excellent mechanical properties could be obtained by three kinds of welding wires. Mechanical properties of welded joints were improved to a certain extent by ER5B06 welding wire, but grain refinement effect of weld was not obvious. Grains of welded joints could be effectively refined and mechanical properties were further improved by ER5B71 welding wire with compound addition of Sc and Zr trace elements. Among the three kinds of welding wires, welded joints with ER5B71 welding wire had the highest strength, and welding coefficient was 83%. The precipitations in welded joints that played the role of grain refinement were mainly Al3(Sc, Zr). At the same time, no matter any kind of welding wire was used, no obvious grain coarsening occurred in welding heat affected zone, which declared that adding Sc and Zr trace elements to base metal could improve softening resistance of the material and effectively inhibit recrystallization behavior of heat-affected zone.Highlights: The method of combining arc physical value simulation and experimental combination was used to conduct research and demonstration to make the research content rich, theoretical depth and more convincing. Aluminum alloy and welding wires with rare earth elements was chosen as the research object, which had a certain guiding significance for the development of new materials and welding materials.