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Metal Casting Technologies : June 2010
METAL Casting Technologies June 2010 41 to slip under shear stress. The number of slip planes and slip directions form slip systems in a metallic crystal. There are only 3 slip systems in hcp crystals, whereas fcc crystals have 12 slip systems. Hence the Mg alloys undergo limited plastic deformation in comparison to Al alloys in general. In other words, crack initiation and propagation under stress would be easier in Mg alloys compared to Al alloys. This factor limits the application of Mg alloys where the components are subjected to service stresses. 3. Burning tendency of Mg at high temperature: Mg is highly prone to oxidation by burning with flame at elevated temperature. Therefore melting and casting of Mg alloys are more difficult compared to Al alloys. In Al alloy melting, there is no such risk of burning. Only the surface layer of Al melt is oxidized, which can be minimized by using covering flux. However, precautions need to be taken in melting and pouring of Mg alloys. Small amount of beryllium ( 0.001 wt%) reduces the tendency of oxidation of surface of Mg alloy melt. Covering fluxes similar to Al alloys are also effective to minimize Mg melt oxidation. During pouring and in the mold, use of a mixture of sulfur and boric acid is common to prevent burning and oxidation of Mg alloy melt, the mixture produces an envelope of SO2 gas and avoid the contact of molten Mg with O2 in air. Solid Mg alloys are less resistant to various corrosive atmospheres compared to Al alloys. Although both alloys lies close in the Ellingham Diagram, Al forms an impervious layer of Al2O3 over its surface, which prevents further oxidation. 4. Thermal conductivity: Al alloys possess higher thermal conductivity than Mg alloys. Hence Al alloys are preferred to Mg alloys for applications requiring higher thermal conductivity (e.g. piston of IC engines). 5. Damping Capacity: The Mg alloys have better damping capacity than Al alloys. It is one property, which is important in applications where components are subjected to vibration. Mg alloys should be preferred to Al alloys where this property is significant. In conclusion, the major limitations in terms of poor toughness and high tendency to oxidation of Mg alloys needs to be addressed to utilize the beneficial lightness of Mg alloys for more applications. ■ Nanjiang Industrial Park,Sihui.Guangdong province.P.R.China. Tel: 0086/758/3855723 Fax: 0086/758/3851719 Mob: 0086/13928640298 Web: www.aidaalloys.com Email: email@example.com Company Introduction Aida Aluminum Alloys Co., Ltd. Located in Nanjiang Industries Zone, Sihui city, Guangdong province, Sihui Aida Aluminum Alloys Co. Ltd. is a well known leading Tibor (altib) Rod and AlMn75, AlFe75, AlTi75 additives producer and supplier in aluminum Industry. Aida have a plant in sihui city, two offices in shenzhen and Nanhai city. Aida alloys company, which was established in 1991,it has many years of experience in non-ferrous alloy industry. As ISO9001 certified supplier of auxiliary materials, Aida research, developing and produce auxiliary materials for Aluminum smelting industry. Aida has various products and materials which were designed to meet the specific demands of foundries around the world. These products are traditionally divided into a range of Tibor Rod Grain Refiner, alloying tablets (element additives), aluminum master alloys, fluxes agent (specialized fluxes). By close cooperation with famous universities and research institutes, Aida not only owns itself Know-How technology, but also having good manufacturing facilities, which were provided by many domestic and international companies. Aida sells high quality products worldwide to meet our customer demands.