Effect of Bolt CTE on Bolt Load Retention for Mg Alloys

The automobile and light truck industries are increasing considering the use of magnesium castings in structural and elevated-temperature applications. Unfortunately, the bolt load compressive stress retention behavior of magnesium alloys is unacceptable for most elevated temperature applications. In this investigation, the effects of bolt strength and the mis-match in the coefficient of thermal expansion (CTE) of magnesium alloy AZ91D and the bolt material has been determined for a wide range of materials (martensitic steel, austenitic stainless steel, ductile iron and aluminum alloys). Also, the effect of heat treating the magnesium alloy, the effect of re-tightening the bolts after the first thermal cycle and the maximum load carry capacity of numerous bolt materials were determined. Corrosion was not considered.