Influence of Aluminum Content on Corrosion Resistance of Mg-Al Alloys Containing Copper and Zinc

The corrosion resistance of Mg-Al alloys deteriorates significantly with increasing copper content. Consequently, the tolerance limit of copper is commonly fixed at less than 300 ppm in Mg-Al alloys to ensure they have sufficient corrosion resistance. However, it is desirable to use higher copper tolerance limit in actual operations. To realize this, it is very important to prevent the deterioration in the corrosion resistance with increasing copper content. In this study, Mg-Al alloys with different aluminum, zinc, and copper contents were casted by high-pressure die casting and the corrosion resistances of the castings were investigated. The corrosion resistance of Mg-9% Al alloys decreased significantly with increasing copper content. However, adding zinc to copper-rich alloys prevented the reduction in the corrosion resistance due to copper. The corrosion rate of Mg-Al alloys containing 0.5% copper and 3% zinc was minimized at an aluminum content of 9%. The corrosion resistance of Mg-Al alloys containing copper and zinc was highest at a zinc content of over 3% and an aluminum content of about 9%.