An Insight into Environment-Conscious (ECO) Magnesium: A Review


Magnesium (Mg) is the lightest metallic structural material and the urge to reduce the weight of vehicles and improving fuel efficiency has inevitably resulted in the long-time exposure of Mg alloys to elevated temperatures (above 200 ℃). Calcium (Ca) addition has been considered as cheap and practical solution to overcome high reactivity and ignition risks of Mg and its alloys. Besides, Ca-bearing Mg alloys are capable of air casting. The recently-developed Environment-conscious (ECO) manufacturing route is novel method of Ca addition, which utilizes CaO to produce Ca-containing Mg alloys and it is thermodynamically proved that this reaction is possible. Elemental calcium is very reactive and needs special requirements in terms of handling. On the other hand, CaO is much cheaper than Ca and can be handled safely due to its good stability. It is also proved that CaO-added Mg has higher melt fluidity than its Ca-added counterpart. The retarded oxidation and ignition of Ca-bearing Mg are reported to be the outcome of dense oxide film made up of CaO and MgO. This report provides comprehensive review of the current literature regarding high-temperature oxidation of Ca-bearing Mg and its alloys. Because commercial Mg casting alloys are mostly based on the Mg-Al system the effect of Aluminum (Al) on ignition and oxidation has also been reviewed.
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