Post-processing heat treatment of lightweight magnesium alloys fabricated by additive manufacturing: a review

Additive manufactured magnesium (Mg) alloys have widespread applications in the medical industry as orthopedic implants and biomedical stents, and in the transportation/ automotive industry due to their status as the lightest structural metallic alloys. The printability of Mg alloys is challenging due to the high oxidization rate, rapid evaporation, and susceptibility to gas trapping. Accordingly, there might be many defects in the as-built parts such as cracking and delamination, porosity and lack of fusion, residual/thermal stresses and distortion, inhomogeneous/columnar microstructure, anisotropy in me-chanical/physical properties, inclusions, and non-equilibrium phases formed during so-lidification. The removal of these defects has a great practical significance, where the post -processing heat treatments without altering the geometry of the parts are often sought in this regard. Accordingly, the present overview article focuses on and critically discusses the recent progress/advances in the application of hot isostatic pressing (HIP), solution annealing (solutionizing), and aging/precipitation heat treatment for the modification/ homogenization of the microstructure and improvement of mechanical/functional prop-erties of Mg alloys for the first time. The main fabrication methods are selective laser melting (SLM) from the category of powder bed fusion (PBF) processes, as well as wire and arc additive manufacturing (WAAM) from the category of directed energy deposition (DED) processes. Moreover, the adaptation of the friction stir processing (FSP) technology into additive manufacturing for grain refinement via dynamic recrystallization (DRX) and defect/pore closure (due to the elevated-temperature thermomechanical processing ef-fects), combined severe plastic deformation (SPD) and thermal post-processing, hybridi-zation of additive manufacturing for Mg alloys, and future prospects have been summarized. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Additive manufactured magnesium alloys have wide applications in the medical and automotive industries. However, the printability of these alloys is challenging and often results in various defects. This overview article critically discusses recent advances in hot isostatic pressing, solution annealing, and aging/precipitation heat treatment for improving the microstructure and mechanical/functional properties of magnesium alloys.