Corrosion behaviors of CoCrWAlx alloys by laser additive manufacturing in molten Al

Xudong Yang a, Chuanwei Li a,b,*, Zhenhua Ye a, Xinyu Zhang a, Mengyao Zheng a, Jianfeng Gu a,b,*, Jiali Jiang c

a Institute of Materials Modification and Modeling, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China

b Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240, China

c IKD Co.,Ltd., Ningbo 315000, China

ABSTRACT

The CoCrW alloy was widely used for aluminum alloy die-casting mold of auto industry owing to excellent high temperature strength and corrosion resistance. However, the corrosion mechanism of cobalt-based alloy in molten Al has not been researched clearly, which inhibited improvement in resisting corrosion and service performance further. The CoCrWAlx alloys were prepared by direct laser deposition and the wetting and corrosion mechanism in molten Al were investigated. The microstructures of CoCrWAlx alloys and solid-liquid interface reaction products were characterized comprehensively. The CoCrWAlx alloys contained cobalt solid solution and precipitates that increased with Al. The reaction interfacial structure was composed of five sublayers: alloy substrate, two products sub-layers, diffusion layer and solidified Al, and reaction products were identified to Al9Co2, Al5Co2 and Al45Cr7 phases. The growth kinetics of product layer and sub-layers were investigated and corresponding theoretical growth models of single and double compound layers were established. The effects of Al addition on corrosion resistance of cobalt-based alloys were analyzed with experiment and phase boundary wetting theory. The 2Al alloy obtained the lowest rate of product layer growth and corrosion loss among all alloys due to increased precipitates and strengthening matrix reduced both reaction-diffusion of molten Al and dissolved alloy substrate. The intrinsic affecting mechanism of adding Al into alloy to resist molten Al was investigated and provided an effective way to improve the corrosion resistance.