Formation of <I>In Situ</I> Composite Layer on Magnesium Alloy Surface by Casting Process

Abstract

In order to develop a process to obtain a functional layer on the surface of a magnesium alloy, the composite layer including in situ Mg 2 Si was formed on the surface by a gravity die-casting. The optimum fabrication condition to form the composite layer and the formation mechanism of the layer were clarified by observing the microstructure, and then the wear properties of the composite layer were also investigated. By casting the magnesium alloy melt into the permanent mold on which the slurry mainly consisting of Si particles was coated, the magnesium alloy composite layer in which the in situ Mg 2 Si particles were dispersed was formed. The melt temperature and mold temperature required to form the composite layer, which perfectly covers the casting, were above 1073 K and above 673 K, respectively. The composite layer was a magnesium alloy in which the fine Mg 2 Si particles of approximately 40 vol% were dispersed. The thickness and hardness of the layer was about 600 μm and 180 HV, respectively. Under the dry sliding wear, the weight loss of the composite layer was lower than that of the magnesium alloy. These results lead to the conclusion that the wear resistant magnesium alloy composite layer in which the in situ Mg 2 Si particles were dispersed can be formed in the present process.