Microstructure and impact mechanical properties of multi-layer and multi-pass TIG welded joints of Al−Zn−Mg alloy plates

Abstract

Abstract The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al−Zn−Mg alloy plates were studied. The phase constituent and microstructure of different regions of the welded joints were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy disperse spectrum (EDS), while the mechanical properties were evaluated according to the impact test. A dispersively distributed spherical and needle-like η(MgZn2) phase was obtained in the welding seam. The phase composition of the heat-affected zone (HAZ) was α(Al)+η(MgZn2)+Al6Mn, and there were a large number of dispersively precipitated nanoscale particles. The welded joint zone had the highest impact toughness as compared with the other parts of the joint. The MgZn2 phase in the weld zone contributed to the improved toughness of the joint. Al2MgCu phase in HAZ was proven to act as a crack source during fracture.