Thermal and Corrosive Aspects of Processing Molten Magnesium

Molten or semisolid metallic alloys exert detrimental effects on materials they contact. Material degradation results from two factors: (i) corrosive attack and (ii) thermal effects due to high temperatures. Corrosion, caused by a liquid metal, is expressed most often by chemical dissolution, metal-to-metal alloying, embrittlement and cracking. A simple containment of a molten alloy during such operations as melting, recycling or conveyance involves mainly corrosion. However, die casting, injection molding and other processing techniques involve also cyclic pressurizing of the melt, which generates stress and activates mechanisms of structural changes at high temperatures. In an industrial environment both factors act simultaneously, causing multiple and complex mechanisms of material degradation. Moreover, corrosion and wear of hardware result in a contamination of the melt and reduction of product quality. For example, the resistance of magnesium alloys to atmospheric corrosion is sensitive to tiny contents of certain metallic impurities.