Abstract

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.

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