Effect of Ag buffer layer thickness on the microstructure and hardness distribution of Cu alloy coating on Al substrate

Abstract

The alloy coating is commonly used to enhance the hardness and wear resistance of Al substrate. However, the coating always cracks because of the brittle intermetallic compound (IMC) and thermal stress. In this investigation, the Ag buffer layer was employed to fabricate the crack-free Cu alloy coating. The effect of thickness of the Ag buffer on the phase transformation and hardness of Cu alloy coating was systematically investigated. The results showed that a thinner Ag buffer contributed to the dissolution of more Al and less Ag in the Cu alloy coating due to the dissolving of high-Al region of Ag buffer layer. A lower content of Ag in the Cu alloy coating brought more primary Cu-rich phase. The high Al in the Cu alloy coating contributed to the formation of β phase. During cooling stage, the β phase transformed into β′ phase through martensitic transformation. The more fine-grained β′ phase contributed to a higher hardness of 310 HV of the Cu alloy coating on the Ag buffer layer with a thickness of 450 μm. The thicker buffer layer contributed to the coating with less Al and more Ag. The Cu alloy coating exhibited a microstructure with more eutectic phase. The primary Cu-rich phase became Cu solid solution due to the lower Al concentration. The coarse-grained primary Cu solid solution and low-hardness eutectic phase contributed to the low hardness of 275 HV.