Abstract
Pickling, zincate, chemical conversion, and electroplating processes were examined and optimized to obtain highly corrosion-protective coatings on AZ91D and AZ31 Mg alloys based on aspects of corrosion control in respective processes. The Pickling process bath composition was adjusted to suppress pitting corrosion and galvanic coupling corrosion between the α-phase and the β-phase to produce a flat dissolution surface. Potentiostatic anodic polarization was applied in the stannate chemical conversion process to an alloy specimen immersed in the conversion bath, thereby supplying sufficient Mg2+ ions to induce formation of a dense and uniform conversion coating. With the zincate process, Cu pretreatment in the precursory activation process enabled dense and uniform Zn deposition suitable for the plating process. Using these methods and conditions, better corrosion-protective coatings with dense, uniform, low-defective and high-adhesive properties were obtained on Mg alloys.
