Characterization of monolayer and single-pass pure Cu coatings applied to 6061 T6 Al alloy and AZ31B Mg alloy substrates using high-pressure cold spray technology

Abstract

The study of monolayer and single-pass pure Cu coatings deposited on distinct substrates using high-pressure cold spray technique is crucial for advancing the application of Cu coatings. However research in this area remains limited. This study systematically investigated the deposition of monolayer and single-pass Cu coatings on 6061 T6 Al alloy and AZ31B Mg alloy substrates with different surface finishes using high-pressure cold spray technology. Notably, while the previous studies have primarily employed gas pressure up to 5 MPa, this work extended the pressure boundary to 5.5 MPa, significantly enhancing coating performance. Comprehensive analyses of coating morphology, thickness, microstructure, and porosity were conducted using three-dimensional profilometry, optical microscopy, and scanning electron microscopy. The optimization of gas temperature and gas pressure significantly enhanced the shear strength of the Cu coatings on both substrates, with bonding mechanisms similar to explosive welding. Higher gas pressure facilitated thermal softening and deeper particle penetration, leading to increased shear strength. The Cu coating deposited on the sandblasted AZ31B Mg alloy substrate at 5.5 MPa and 800 °C exhibited a remarkable shear strength of 136.43 MPa. Furthermore, the microhardness of the Cu coatings increased with gas pressure due to work-hardening effects and reduced porosity. Specifically, the Cu coating deposited on the sandblasted 6061 T6 Al alloy substrate at 5.5 MPa and 600 °C reached a microhardness of 206.18 HV, while the porosity of the Cu coating deposited at 5.5 MPa and 800 °C was as low as 0.26 %. The surface roughness of the substrates also played a crucial role in coating performance; grit-blasting led to thicker coatings and enhanced shear strength due to more effective particle filling. In summary, Cu coatings deposited on sandblasted 6061 T6 Al alloy plates at 5.5 MPa and 800 °C achieved a thickness of 486.37 μm, a shear strength of 60.5 MPa and a surface roughness of 8.87 μm. This study provides valuable insights into the effects of process parameters on coating properties, contributing to the broader application of high performance Cu coatings.