Evolution of Microstructure and Dispersoids in Al-Mg 5xxx Alloys Under Wire + Arc Additive Manufacturing and Permanent Mold Casting

The microstructure and the formation of dispersoids in Al-Mg 5xxx alloys under wire + arc additive manufacturing (WAAM) and permanent mold casting (PM) were investigated with the aid of optical microscopy and scanning/transmission electron microscopies. In the as-deposited/as-cast condition, the grains and intermetallics in WAAM sample are finer, and its related microhardness is higher than PM sample. However, during the heat treatment at 425 ℃, the formation of dispersoids in WAAM sample is slower with bigger size and lower volume, leading to its lower microhardness than PM sample. In addition, the area fraction of the dispersoid zone in WAAM sample is much lower than PM sample. Two types of dispersoids are observed in both WAAM and PM samples. The formation and distribution of dispersoids during heat treatment have been characterized aiming to discover the influence of fabrication processes (WAAM and PM) on the precipitation behavior of dispersoids.