Effect of scratch on corrosion resistance of calcium phosphate conversion coated AZ80 magnesium alloy
(1. State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing 400044, China;
2. National Engineering Research Center for Magnesium Alloy, Chongqing University, Chongqing 400044, China;
3. Qinghai Salt Lake Industry Co., Ltd., Qinghai 816000, China;
4. Center for Marine Materials Corrosion and Protection, College of Materials, Xiamen University, Xiamen 361005, China;
5. School of Mechanical and Mining Engineering, The University of Queensland, Brisbane Qld 4072, Australia)
2. National Engineering Research Center for Magnesium Alloy, Chongqing University, Chongqing 400044, China;
3. Qinghai Salt Lake Industry Co., Ltd., Qinghai 816000, China;
4. Center for Marine Materials Corrosion and Protection, College of Materials, Xiamen University, Xiamen 361005, China;
5. School of Mechanical and Mining Engineering, The University of Queensland, Brisbane Qld 4072, Australia)
Abstract: In order to analyze the effect of scratch on the corrosion behaviour of a calcium phosphate conversion coating (CPCC) on AZ80, the electrochemical testing, scanning vibrating electrode technique (SVET), immersion test and hydrogen evolution experiment were performed to study the corrosion resistance of AZ80, AZ80 with CPCC and coated AZ80 with scratch. The results show that the coating improves the corrosion resistance of the AZ80 from a current density of (85±4) to (4±1) μA/cm2. When the coating was damaged, its protection on substrate would be reduced. The scratch with a length of around 12 mm on the coating reduced the corrosion resistance to a current density of (39±1) μA/cm2. In addition, the corrosion occurred initially in the scratch area and the corrosion site first occurred at the junction of the scratch and the coating. Besides, the micro corrosion mechanism of the specimen containing scratch was clarified.
Key words: magnesium alloy; AZ80 alloy; scratch; conversion coating; corrosion resistance; scanning vibrating electrode technique (SVET)