Deposition mechanism of cathodic electrophoresis coating on Mg alloys: Effects of Mg substrates on deposition process

Cathodic electrophoresis is an ideal surface treatment technology for Mg alloys, but the effect of Mg substrates on the electrophoresis process lacks sufficient research. Thus, the electrophoretic painting (EP) coatings were prepared on pure Mg, AZ31 and AZ80 Mg alloys, and the effect of Mg substrates on the properties and deposition process of the EP coatings was investigated by current-time (I-t) curves, contact angle, and electrochemical measurements. The results indicate that the surface energy of Mg substrates greatly affects the physical adsorption of EP particles, and the AZ80 with the highest surface energy adsorbs the most paint particles in the "electroless deposition" stage. The effect of "electrodeless deposition" enhances the differences of microstructure on the material surface, affecting the value of the instantaneous current for the initial electrophoretic deposition, with very little effect on the subsequent electrophoretic deposition. And AZ31 exhibits the highest cathodic hydrogen evolution rate during electrophoresis process, resulting in the largest EP coating thickness, but with the most defects.