The effect of Cu rejection in laser forming of AlCoCrCuFeNi/Mg composite coating

AlCoCrCuFeNi/Mg composite coating was formed by means of laser melt injection using a direct blown powder method with the aim of investigating the effect of Cu rejection in laser forming of AlCoCrCuFeNi high-entropy alloy (HEA) particle reinforced composite coating on magnesium substrates. It is found that the distribution of rejected Cu was uneven within the formed coating. As a distance from the substrate increased, a higher Cu content was detected in the area between the reinforcing HEA particles. Accordingly, the dendritic and cellular structures of CuMg₂ were obtained in the upper region of the composite coating due to a high Cu content. With the Cu concentration decreasing, the microstructure was gradually dominated by columnar Mg when moving towards the substrate. Although microhardness values increased, room temperature dry sliding wear properties of the formed coating were adversely influenced by the Cu rejection due to the formation of the brittle CuMg₂ phase. Additionally, the Cu rejection could promote the BCC-structured formation within the HEA particles, and therefore it may cause a change in deformation behavior of the reinforcement due to the increase of hardness and the decrease of plasticity of the reinforcing HEA particles.