The Influence of Reinforcement Purity on Corrosion Resistance of AM50/SiC Composites

Abstract

The microstructure and corrosion behaviour of AM50/SiC magnesium matrix composites reinforced with SiC particles were investigated. Composites containing 10 wt. % of SiC were fabricated by means of gravity casting. Technical grade silicon carbide used for the composites fabrication was subjected to a purification procedure leading to the removal of iron containing impurities from its surface. The corrosion resistance of the composite with purified SiC particles was compared to the corrosion resistance of the one containing crude technical grade silicon carbide as well as to the corrosion resistance of the matrix alloy. Voltammetry and an electrochemical noise technique as well as hydrogen evolution rate measurements were utilized for that purpose. Corrosion tests were performed in 0.5 mol dm3 NaCl saturated with Mg (OH)2. It has been demonstrated that the composite containing purified SiC was less susceptible to corrosion than the one containing crude SiC particles. Both composites were less resistant to corrosion than their matrix itself. Regardless of a purity level of SiC which was used for the composites fabrication, the same constituents were revealed in their microstructure, namely: α-phase (a solid solution of aluminium in magnesium), fully divorced eutectic α + γ (where γ-phase is Al12Mg17), intermetallic compound Al8Mn5 and SiC particles uniformly distributed in the whole volume of the matrix.