Anodized magnesium coating (ANOMAG) AZ91D: corrosion protection and fatigue performance

摘要

A novel, environmentally friendly, anodizing process for magnesium was developed in New Zealand and has been up-scaled to a full production plant. The anodized coating on AZ91D magnesium alloy was evaluated in terms of corrosion resistance and tensile fatigue (in air). This paper reports the test results, which are very encouraging showing corrosion protection performance of up to 1000 hours of salt (fog) spray exposure. The additional process of colouring with dyes appears to have no effect on the corrosion protection performance provided by the coating. The tensile fatigue results indicate that the 20 μm coating slightly reduces the fatigue strength compared to the uncoated magnesium alloy but significantly reduced the range of results at high stresses, making the fatigue properties more predictable. The corrosion resistance of the coating, combined with the high strength-to-weight ratio of magnesium, makes this coating process particularly attractive to the automotive and aerospace industries where a low-cost and relatively high performing corrosion resistant anodized coating for magnesium alloys has been sought for many decades.