Corrosion and corrosion prevention of magnesium alloys

Introduction of high purity alloys improved the corrosion resistance of magnesium alloys significantly. This has led to an increased use of magnesium for components like valve covers, transmission housing, and gear box housing. Because of the unnoble nature of magnesium, galvanic corrosion is the main challenge when magnesium is used in corrosive environment. By proper material selection, proper design and selective use of coatings and insulation materials, the risk for galvanic corrosion is significantly reduced. Test results show that fasteners made of aluminium of the 6000 series reduce galvanic corrosion of magnesium to very low levels in salt spray tests. Combinations of plated steel fasteners and aluminium washers are very efficient for galvanic corrosion prevention. Furthermore, it seems that sealed zinc plating is the best type of plating for steel fasteners. The plating must, however, be free from defects and the bolt head design is an important factor to get a high quality plating.