Study on hot cracks and mechanical properties of MIG-welded T-joints of high-strength aluminum alloy under different rolling directions

As the operating speed of high-speed railways increases, higher requirements are imposed on the welding quality of high-speed train bodies. The influence of Al-Zn-Mg high-strength aluminum alloy plates with different rolling directions on the hot cracks, microstructure, and mechanical properties of MIG-welded T-joints was systematically studied. The research results show that when the welding direction is parallel to the rolling direction, abnormally grown coarse grains appear near the partial the fusion zone. The eutectic phases Al (FeMnSi) and MgZn with low melting points located on the grain boundaries are heated and melted to form a liquid film during the welding process, and then liquefaction cracks are formed due to the action of welding thermal stress. Liquefaction cracks are generally present in the partial the fusion zone. When the welding direction is parallel to the rolling direction, the number of medium and long liquefaction cracks in the partial the fusion zone significantly increases. By changing the rolling direction of the base material, the number of liquefaction cracks is significantly reduced, and the microhardness, tensile strength, and elongation of the welded joint are improved, reaching 99.81 HV, 321.1 MPa, and 37.7%, respectively. The tensile specimen shows the characteristics of both tough and brittle fractures.