MAGNESIUM ALLOYS: LIGHT, STRONG, AND CORROSION RESISTANT

摘要

THE LIGHTEST of all structural metals, magnesium, is 30 percent lighter than aluminium and 75 percent lighter than steel. Based on the material's occurrence on the earth's crust, magnesium is the third most abundant after aluminium and iron, and there are estimated to be 6,000,000 tonnes of magnesium per cubic mile of seawater, according to the Scientific American. Although the metal alone has poor corrosion-resistant performance, a range of new high-purity alloys that have been developed have corrosion resistance better than carbon, steel, and some aluminium alloys. In the paper on pages 142-163 of this issue, the authors provide a wide-ranging and useful review of this metal and its alloys, how they are manufactured, and how their corrosion-performance compares. Magnesium has both a higher strength-to-weight ratio and a higher tensile strength per unit weight than steel; it is also stiffer than most engineering plastics, has good dimensional stability, and has excellent resistance to impact and minimal distortion. Magnesium has very good damping qualities, absorbing both noise and vibration, and it provides an excellent shield against harmful electromagnetic radiation and radio-frequency interference. The metal has ideal casting properties, and can be moulded into large, thin-walled components for which secondary machining is rarely necessary. Quick to melt and cool, magnesium ensures high castingrates, extended die life, and low tooling costs. Despite these obvious advantages, however, the use of the metal has traditionally been limited because it is highly active, and very much prone to corrosion attack. Its poor corrosion-, wear-, and creep-resistance when compared to other structural metals make it unsuitable for many applications; yet, recently, its use is showing a marked increase in the automobile and aerospace industry.