Magnesium Recycling: State-of-the-Art Developments, Part I


The primary production of magnesium has been increasing over the last 15 years approaching the mark of one million tonnes per year. Though this amount is still much less than the annual world production of steel or aluminum, a steadily growing fraction of primary magnesium is used for the fabrication of magnesium alloys for automotive components like gearbox housings, dashboard panel carriers, and steering wheels. The recycling of magnesium, however, has always been an issue. These days it is especially important due to its energy intensive production. Using the economic electrolytic process consumes 35 kWh/kg, and remelting magnesium consumes 10% of this energy at the most. High pressure die casting (HPDC) is by far the most established fabrication method for magnesium alloy components and the automotive industry is by far the most important user of magnesium alloys. About 50% of a HPDC shot is made up by biscuit or sprue, runner system, and gates. This excess metal is relatively clean, sorted according to a single alloy, and can be remelted easily. It is estimated that approximately 200,000 tonnes of clean magnesium scrap are recycled and reused together with primary magnesium metal in the HPDC process. However, automotive magnesium components at the end of a products lifetime have not been recycled so far. The latter is due to the decreasing corrosion resistance of magnesium alloys with elevated contents of copper, nickel, and iron. In this article, sources of scrap, sorting techniques, scrap classes, and the influence of oxides, in magnesium melts is presented.
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