Electrodeposition of Cu coating with high corrosion resistance on Mg-3.0Nd-0.2Zn-0.4Zr magnesium alloy
(1. National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiao Tong University,
Shanghai 200240, China;
2. State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China)
Shanghai 200240, China;
2. State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China)
Abstract: To improve the corrosion resistance, electrodeposition of Cu coating on Mg-3.0Nd-0.2Zn-0.4Zr (mass fraction, % NZ30K) magnesium alloy via an appropriate pretreatment was investigated. The surface morphologies, compositions and microstructures of the pretreated films and Cu coating were characterized in detail. The results show that the activation film consists of fluoride and phosphates and Zn immersion film forms preferentially on the eutectic compound Mg12Nd phase region. A smooth, uniform and dense Cu coating is successfully obtained. Potentiodynamic polarization tests reveal that Cu coating can greatly improve the corrosion resistance of NZ30K magnesium alloy. Open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) tests during long-term immersion further demonstrate that Cu coating can provide an effective protection for NZ30K magnesium alloy from corrosion up to ~60 h, due to its dense structure and a stable passive film formed. In addition, Cu coating exhibits good adhesion to substrate as confirmed by thermal shock test.
Key words: NZ30K magnesium alloy; pretreatment; Cu electrodeposition; corrosion resistance; adhesion