Surface modification of magnesium alloys using thermal and solid-state cold spray processes: Challenges and latest progresses

Potential engineering applications of magnesium (Mg) and Mg-based alloys, as the lightest structural metal, have made them a popular subject of study. However, the inferior corrosion and wear characteristics significantly limit their application range. It is widely recognized that surface treatment is the most commonly utilized technique for remarkably improving a substrate's surface characteristics. Numerous methods have been introduced for the surface treatment of Mg and Mg-based alloys to improve their corrosion behavior and tribological performance. Among these, thermal spray (TS) technology provides several methods for deposition of various functional metallic, ceramic, cermet, or other coatings tailored to particular conditions. Recent researches have shown the tremendous potential for thermal spray coated Mg alloys for biomedical and industrial applications. In this context, the cold spray (CS) method, as a comparatively new TS coating technique, can generate the coating layer using kinetic energy rather than combined thermal and kinetic energies, like the high-velocity oxy-fuel (HVOF) spray method. Moreover, the CS process, as a revolutionary method, is able to repair and refurbish with a faster turnaround time; it also provides solutions that do not require dealing with the thermal stresses that are part of the other repair processes, such as welding or other TS processes using a high-temperature flame. In this review paper, the recently designed coatings that are specifically applied to Mg alloys (primarily for industrial applications) employing various coating processes are reviewed. Because of the increased utilization of CS technology for both 3D printed (additively manufactured) coatings and repair of structurally critical components, the most recent CS methods for the surface treatment, repair, and refurbishment of Mg alloys as well as their benefits and restrictions are then discussed and reviewed in detail. Lastly, the prospects of this field of study are briefly discussed, along with a summary of the presented work.