Influence of heat treatment on corrosion behavior of Al–Mn–Mg–Sc–Zr alloy produced by laser powder bed fusion

Effect of heat treatments on the microstructure and corrosion behavior of Al–Mn–Mg–Sc–Zr alloy fabricated by laser powder bed fusion (LPBF) were systematically investigated. The results demonstrate that the 300 °C/5 h heat-treatment doesn't alter the typical bimodal grain distribution of LPBF-fabricated alloy. However, the grains at molten pool boundaries experience a significant growth after a 500 °C/5 h heat treatment, narrowing the gap of grain size between fine-grain (FG) region and coarse-grain (CG) region. It is also found that the heat treatments have an impact on Al3(Sc, Zr) and Al6(Mn, Fe) precipitates. Detailedly, the Al3(Sc, Zr) precipitates undergo a slight growth in size and obvious increase in quantity after heat treatment whilst the Al6(Mn, Fe) particles go through a rapid increase both in amount and size, especially for the alloy after being subject to a higher temperature heat treatment. As consequence, the heat-treated LPBF aluminum alloys exhibit worse corrosion resistance compared with their original state. The Al3(Sc, Zr) precipitates acting as micro-cathodes at molten pool boundaries accelerate the preferential corrosion of fine grain regions of 300 °C/5 h heat-treated alloy (HT-300). In contrast, the 500 °C/5 h heat-treated alloy (HT-500) tends to promote a more uniform corrosion due to the dissolution of the homogeneously distributed Al6(Mn, Fe) anodes on the alloy surface.