A newly designed NiP duplex coating on friction stir welding joint of 6061-T6 aluminum

Friction stir welding (FSW) joints often require coatings with good adhesion and corrosion resistance to improve durability. In this research, a newly designed duplex NiP coating was fabricated on the FSW joint of 6061-T6 aluminum alloy. An anodic aluminum oxide (AAO) layer was formed on the joint substrate as the intermediate layer to enhance adhesion, and a NiP layer was then electroplated on top to strengthen the corrosion and wear properties. The bonding strength, anti-corrosion property and wear resistance of the duplex NiP coating were investigated systematically and compared with those of the traditional zincated NiP coating. The duplex NiP coating results in superior adhesion and significantly improved anti-corrosion property than traditional NiP coating. The friction property of the FSW joint with duplex NiP coating is 88 % higher than that of the original FSW joint and 75 % higher than that of the FSW joint coated with traditional NiP coating. The related mechanisms were discussed in detail.