Protection of Mg Alloys for Structural Applications in Automobiles

Magnesium alloys, with the highest strength-to-weight ratio of the common engineering alloys, have been used in castings of various automotive components. The forecast trend for the use of the metal in automobiles suggests a more rapid growth pace in the coming decade. However, Mg alloys happen to be among the most reactive materials in natural environments, such as those applicable to the exterior automotive conditions. The most challenging form of corrosion is galvanic corrosion: the corrosion of Mg parts when in contact with other materials such as coated steel bolts and nuts. In the joining areas, crevice corrosion can also be a concern. Effective coatings are essential for such applications. In the research work that is undertaken at the Materials Technology Laboratory of Natural Resources Canada in partnership with a major USAMP (US DOE) program, an effort was made to select environmentally friendly coatings for Mg alloys and to evaluate new coatings for steel fasteners and new alloys for use as washers and spacers. The results of laboratory tests are presented in this paper. Effort was also made to develop a new washer material that can minimize the galvanic corrosion between the Mg alloy and the fasteners; preliminary test result of this material is also provided.