Improvement of Corrosion Resistance of the AZ91 Magnesium Alloys with Sputtered Aluminum Layer Using Interdiffusion Treatment, Anodic Oxidation Treatment and Sealing Process

Abstract

Magnesium alloys have low corrosion resistance due to their high chemical activity. Therefore, it is necessary to improve their corrosion resistance to use in corrosive environments. In the present study, we aimed to improve the corrosion resistance of AZ91 magnesium alloy in NaCl solution, using aluminum sputtering deposition, anodic oxidation treatment and sealing process were examined. To evaluate the corrosion rate, electrochemical experiments were carried out. In the case of just aluminum sputtering deposition, corrosion resistance was not improved due to small defects in the sputtering deposition. However, corrosion resistance was improved by sputtering deposition followed by interdiffusion treatment at 553 K for more than 3 hours. Corrosion resistance was further improved by anodic oxidation treatment and sealing process after the interdiffusion treatment. With this series of treatments, the corrosion rate of the samples was reduced to 1/360 compared to that of AZ91 base metal. The results show that the interdiffusion treatment, anodic oxidation treatment and sealing process after sputtering deposition are significantly effective to improve corrosion resistance of AZ91 magnesium alloy.

Fig. 8 Corrosion rate and Corrosion potential of samples measured in 3.5 mass% NaCl solution at 298 K; (a) AZ91 substrate, (b) AZ91 substrate with Al film as-deposited, (c) AZ91 substrate with Al film deposited and interdiffusion treatment at 553 K for 1 hour, (d) for 3 hours, and (e) for 9 hours. (f) AZ91 substrate with Al film deposited and interdiffusion treatment at 553 K for 9 hours, followed by anodized and hot water sealing. In reference data: (g) Al/AZ91D with AAO treatment 15 min.²⁸⁾