H ayder Ahmad

Abstract

Magnesium alloys are widely used in aerospace and automotive industries due to their superior density to strength ratio (high specific strength) compared with other structural materials. They also provide a number of attractive properties such as dimensional stability, good heat dissipation and good damping effects. Furthermore, magnesium alloys provide a more cost-effective solution compared to other high strength metals.

Therefore, many researchers carried out the study of the microstructure, physical and mechanical specification and manufacturability (casting, forging, machining, weldability –etc) of the Magnesium and its alloys.

Casting is one of the common techniques used to manufacture parts out of the Magnesium alloys. Despite the fact that casting is a good manufacturing process for mass production and cost effective process, it has problems. For example, the microstructures of these castings tend to be coarse with large grain size that will influence the mechanical properties. Furthermore, the crystal structure of the magnesium alloys are hexagonal close packed (HCP) structure which make the materials more brittle, which provides fewer independent slip systems.

The second and most common problem with the sand casting of the magnesium alloys is the potential reaction with the commonly used silica containing as constituents of plaster or shell mould materials. Therefore, the reaction of the Silica with Magnesium produces Magnesium Oxide and Magnesium Silicates.

In this paper, the effects of the Magnesium Silicates on the crack initiation will be studied. The most fascinating part of this study is the propagation of the crack in the magnesium alloys under a static load by what may be the cause of the magnesium hydrogen embrittlement. Detail fractography of the fracture surfaces will be presented in this paper.

Finally, a recommendation to reduce the risk of the Magnesium Silicates will be listed in this study.

Session