Corrosion in Magnesium and Its Alloys

Abstract

Magnesium alloys are mixtures of magnesium with other metals often aluminium, zinc, manganese, silicon, copper, rare earths and zirconium. Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys. Magnesium and its alloys have gained importance over the last decade due to their superior strength to weight ratio. However, corrosion of magnesium alloys is an issue which has not been fully understood. This paper reviews the different types of corrosion prevalent in magnesium and its alloys. Magnesium and magnesium alloys are more prone to galvanic type of corrosion, which can cause deleterious attack in the metal and alloy resulting in reduced mechanical stability level and an ugly appearance. Effect of alloying elements is discussed and few mechanisms of corrosion are thrown light upon. Some biodegradable Magnesium alloys have also been discussed with regard to corrosion. A non-protected magnesium and magnesium alloy clean surface exposed to inside or outside atmospheres free from any salt spray will form a gray film surface that protects the metal from corrosion while causing only very small losses in mechanical properties. Chlorides, sulphates and other foreign materials that hold moisture content on the surface can enhance corrosion and pitting of alloys unless the metal and alloy is protected by surface coatings. The surface film that forms on the magnesium and magnesium alloys exposed to the atmosphere gives lower protection from further attack. In this review, surface treatments of magnesium alloys are also discussed.