Low-pressure Cold Spraying Cu-based Composite Coating On Surface Of AZ91D Magnesium Alloy And Performance

There are various defects in the process of casting,forming and service for AZ91D magnesium alloy parts,resulting in the shortening or failure of service time of magnesium alloy components,so the repair and remanufacturing process of such magnesium alloy components is very important.In this paper,Cu-Ni-Al-Al₂O₃composite coating and Cu-Ni-Al-Al₂O₃composite coating were prepared on the surface of AZ91D magnesium alloy by low pressure cold spraying technology after the powder of Cu-Ni-Al-Al₂O₃composite coating was ball-milled with different parameters to repair and protect AZ91D magnesium alloy components,and the feasibility of extending the service life of magnesium alloy construction by this technology was explored.In this paper,Cu-Ni-Al₂O₃composite coating was first prepared.The morphology,composition and microstructure of Cu-Ni-Al₂O₃coating were analyzed by SEM,EDS,metallographic microscope and XRD.The results showed that the composite coating had good compactness,the phases of the coating were combined tightly,and there were no large pores and perforations.The coating did not have phase transformation during the preparation process.The test results of mechanical properties showed that appropriate Ni content could effectively improve the hardness,bonding strength and wear resistance of the Cu-based composite coating,and could improve the deposition efficiency of the sprayed powder,up to36.3%.The corrosion resistance test results showed that the coating has the best corrosion resistance when the Cu-Ni mass ratio was 7:3,and could maintain long-term stability in corrosive media.In this paper,Cu-21%Ni-Al₂O₃composite coating was doped with different mass fractions of Al to prepare Cu-Ni-Al-Al₂O₃composite coating,with the purpose of further improving the powder deposition effect and coating performance.The test showed that Al doping could improve the compactness of the coating,reduce the porosity to 0.32%,and reduced the residual stress of the coating.The mechanical property test showed that the doping of Al could improve the bonding strength of the coating to 35.9 MPa and reduced the friction coefficient of the coating.When the content of Al was 20%,the hardness of the coating could also be increased to 156 HV_0.1.After doping Al powder,the deposition efficiency of the powder decreased slightly,and the corrosion resistance of the coating decreased significantly.When the content of Al was too high,the coating would crack and perforation.In this paper,the spray powder of Cu-Ni-20%Al-Al₂O₃composite coating was ball milled.After ball milling,the powder morphology changed.When the rotating speed was 200r/min,the powder morphology changed to core-shell structure powder with Al as shell and Cu and Ni as core,and the particle size decreased.After spraying,the density of the coating was improved and the residual stress was increased.When the ball milling speed was 200 r/min,the powder deposition efficiency was 41.6%,and the coating bonding strength reached 40.2MPa.The wear resistance of the coating increased with the increase of ball milling speed,and the hardness of the coating did not change significantly.The corrosion resistance test results of the coating showed that proper ball milling treatment could improve the corrosion resistance of the coating and reduced the adverse effects of Al powder.When the ball milling speed was 200 r/min,the coating protection rate was 96.95%,showing good corrosion resistance.