Inhomogeneity of Microstructure of Aluminum Alloy Welded Joint

Al-Mg-Mn alloy hot-rolled plates with 10mm thick were welded by multipass MIG welding with the Al-Mg wire, and inhomogeneity of microstructure of the welded joint were examined by the methods of metallograph, scanning electron microscope (SEM) and energy spectrum. The results show that the inhomogeneity of microstructure is very obvious in different regions of welded joint. The weld zone is typical cast microstructure, heat affected zone (HAZ) retains the basic characteristics of hot-rolled and partial recrystallization occurs. Because of the grain refining effect of Al3Zr particle, a layer of fine grain structure, in which the grains are remarkably fine, is formed on the weld pool boundary. In two cladding welding interface, because of the similarity of microstructure of both sides, weld grains grow epitaxially along the heat dissipation direction and grain growth is more apparent.