Corrosion fatigue behavior of AM6O magnesium alloy with anodizing layer and chemical-conversion-coating layer

The status of poor corrosion resistance of die cast AM60 magnesium (Mg) alloys can be improved by applying various types of surface coatings above them. However, coating can sometimes alter the fatigue properties and initiation mechanism, which is not reported so far for this group of alloy. Present study focuses on this issue investigating influence of anodizing layer and chemical-conversion-coating layer on corrosion fatigue properties of Mg alloy, AM60. Coating performance was assessed in two different corrosive environments: high humidity (50 degrees C, 80% RH) and 5wt% NaCl medium. The key observation for humid environment was that the chemical-conversion-coating without a painting layer showed better corrosion resistance than that of the anodized layer without a painting layer. Moreover, chemical-conversion-coating with a painting layer can effectively protect the underlying AM60 alloy even under the most severe corrosive environments (5wt% NaCl). Our results show, for the first time, that chemical conversion coating can be successfully used in machine parts loaded in aggressive medium without severely compromising the fatigue strength.