Effects of gas to melt ratio on the microstructure of an Al–10.83Zn–3.39Mg–1.22Cu alloy produced by spray atomization and deposition

• At high GMR, the broken fragments and i-Mg32(AlZn)49 quasicrystal are observed.
• At medium GMR, microstructure consists of α-Al equiaxed grains and MgZn2 phase.
• At low GMR, the coarsened α-Al grains and bcc-Mg32(AlZn)49 eutectic appear.

Various gas to melt ratios (GMR) that govern the cooling rate of spray forming can be achieved through controlling the atomizer form and the atomization pressure. The effect of the GMR on microstructures of an Al–10.83Zn–3.39Mg–1.22Cu alloy produced through spray forming has been studied using electron microscopy. When the GMR is high at 3.5, dendritic structure and quasi-crystalline i-Mg32(AlZn)49 particles inherited from the original powders can be observed. Spray forming at medium GMR of 2.3 produces equiaxed α-Al grains and MgZn2 phase that discontinuously distributes along the grain boundaries and within the grains as small particles. The low GMR of 1.4 corresponds to low cooling rate. Coarse and equiaxed α-Al grains together with eutectic structure consisting of b.c.c.-Mg32(AlZn)49 and α-Al phases along the grain boundaries are obtained.