Post processing of additive manufactured Mg alloys: Current status, challenges, and opportunities

Magnesium (Mg) and its alloys are emerging as a structural material for the aerospace, automobile, and electronics industries, driven by the imperative of weight reduction. They are also drawing notable attention in the medical industries owing to their biodegradability and a lower elastic modulus comparable to bone. The ability to manufacture near-net shape products featuring intricate geometries has sparked huge interest in additive manufacturing (AM) of Mg alloys, reflecting a transformation in the manufacturing sectors. However, AM of Mg alloys presents more formidable challenges due to inherent properties, particularly susceptibility to oxidation, gas trapping, high thermal expansion coefficient, and low solidification temperature. This leads to defects such as porosity, lack of fusion, cracking, delamination, residual stresses, and inhomogeneity, ultimately influencing the mechanical, corrosion, and surface properties of AM Mg alloys. To address these issues, post-processing of AM Mg alloys are often needed to make them suitable for application. The present article reviews all post-processing techniques adapted for AM Mg alloys to date, including heat treatment, hot isostatic pressing, friction stir processing, and surface peening. The utilization of these methods within the hybrid AM process, employing interlayer post-processing, is also discussed. Optimal post-processing conditions are reported, and their influence on the microstructure, mechanical, and corrosion properties are detailed. Additionally, future prospects and research directions are proposed.