Challenges and opportunities in the production of magnesium parts by directed energy deposition processes

Mg-alloys have gained considerable attention in recent years for their outstanding properties such as lightweight, high specific strength, and corrosion resistance, making them attractive for applications in medical, aerospace, automotive, and other transport industries. However, their widespread application is hindered by their low formability at room temperature due to limited slip systems. Cast Mg-alloys have low mechanical properties due to the presence of casting defects such as porosity and anisotropy in addition to the high scrap. While casting methods benefit from established process optimization techniques for these problems, additive manufacturing methods are increasingly replacing casting methods in Mg alloys as they provide more precise control over the microstructure and allow specific grain orientations, potentially enabling easier optimization of anisotropy properties in certain applications. Although metal additive manufacturing (MAM) technology also results in some manufacturing defects such as inhomogeneous microstructural evolution and porosity and additively manufactured Mg alloy parts exhibit lower properties than the wrought parts, they in general exhibit superior properties than the cast counterparts. Thus, MAM is a promising technique to produce Mg alloy parts. Directed energy deposition processes, particularly wire arc directed energy deposition (WA-DED), have emerged as an advantageous additive manufacturing (AM) technique for metallic materials including magnesium alloys, offering advantages such as high deposition rates, improved material efficiency, and reduced production costs compared to subtractive processes. However, the inherent challenges associated with magnesium, such as its high reactivity and susceptibility to oxidation, pose unique hurdles in the application of this technology. This review paper delves into the progress made in the application of DED technology to Mg-alloys, its challenges, and prospects. Furthermore, the predominant imperfections, notably inhomogeneous microstructure evolution and porosity, observed in Mg-alloy components manufactured through DED are discussed. Additionally, the preventive measures implemented to counteract the formation of these defects are explored.