Study on the Effect of Microstructures and Properties of Al-Mg-Mn-Zr Alloy Welding Wire by Adding Minor Sc

Abstract

The low strength of welded joints of aluminum alloy welding wire materials has seriously restricted the promotion and application of high-performance aluminum alloys represented by 7A52 and 7B52 aluminum alloy. It is urgent to develop new high-strength aluminum alloy welding wire material to meet the lightweight application demand of 7××× series high-performance aluminum alloy materials in military and civilian vehicles. This paper studied the effect on microstructures, mechanical properties, and welding properties of Al-6Mg-0.3Mn-0.2Zr welding wire alloys by adding minor Sc elements. The result shows that it formed Al₃Zr, Al₃Sc, and Al₃(Sc_1-x, Zr_x) primary dispersive phases in the matrix, and the Al₃(Sc_1-x, Zr_x) primary phase, which had triple-shell microstructure composed of Al₃Zr/α(Al)/Al₃Sc three-layer phases enclosing individually with each other from the center to outside. These phases could promote heterogeneous nucleation during solidification and crystallization in the process of welding, resulting in strong refinement and strengthening effects in the weld-zone microstructure. The welding joint mechanical properties of both tensile strength and elongation increased with the increase of Sc contents within the range of 0–0.4%. It was reached at Rm 365 MPa/A 5% without means of heat treatment which are much higher than aluminum alloy welding wires used in current engineering when the 7B52 aluminum alloy laminated plates were welded with the prepared welding wire Al-6Mg-0.3Mn-0.2Zr alloys of 0.385% Sc.