Influence of pretreatments on physicochemical properties of Ni-P coatings electrodeposited on aluminum alloy

Abstract

Aluminum often requires protective coatings to prevent corrosion. The aluminum alloy substrate usually needs pretreatment to minimize, stabilize or convert the surface oxide in order to achieve adequate coating adhesion. The electrodeposited Ni-P coating is a promising candidate as a protective coating due to its easy fabrication and excellent performance. This study comprehensively investigates the pretreatment of zincating and anodizing on 6061 aluminum alloy, and systematically discusses their influence on the electrodeposited Ni-P coatings. The crystal structure and elemental composition were investigated for interlayers and Ni-P coatings subsequently, while morphologies of the coating surface and cross-section were also determined. The results revealed similar phase composition for differently pretreated Ni-P coatings, while distinct nodule featured morphology was observed for anodized Ni-P coating. It was found that anodized Ni-P coatings had the best performance due to its superior coating adhesion, wear-resistance, and corrosion resistance. In contrast, severe wear damage was occurred to zincated Ni-P coatings due to its inferior microstructure and weak zinc interlayer. Lastly, the influence of anodizing pretreatment on the coating microstructure is discussed, and a model is proposed for Ni-P electrodeposition employing anodizing pretreatment.

Keywords

• Ni-P
• Electrodeposition
• Anodic oxidation
• Physiochemical property
• Aluminum alloy