Automobiles magnesium alloys

Strength and low density are important properties in the manufacture of airplanes, automobiles, metal luggage, ladders, shovels and other gardening equipment, racing bikes, skis, race cars, cameras, and power tools. A typical magnesium alloy contains about 90 percent magnesium, 2 to 9 percent aluminum, and small amounts of zinc and manganese. 

Magnesium is thermodynamically one of the less noble metals, and it can protect most other metals when used as sacrificial anodes (see Section 10.4). In the atmosphere the metal is covered by an oxide film. Therefore it resists rural atmospheres but is subject to pitting in marine atmospheres. Magnesium alloys are also liable to SCC and erosion corrosion, and are attacked by most acids. Mg alloys are used in automobile engines, aircraft, missiles and various movable and portable equipment, in all cases primarily because of their low density (1.76 g/cm ). 

Magnesium alloys are the lightest of the casting metals, being about 60% as dense as aluminium alloy, and are used where weight saving is important, e.g. for portable saws, cameras, projectors and automobile components including specialised car wheels. The specification of these alloys is contained in BS EN 1753. 

Pure magnesium metal is lighter in weight than aluminum and, thus, would make an excellent construction metal were it not for its high reactivity and flammability at a rather low temperature when compared to other metals. It is an excellent metal to alloy with other metals for use in the aircraft, space, and automobile industries. 

Aluminum is a very versatile metal with many uses in today s economy, the most common of which are in construction, in the aviation-space industries, and in the home and automobile industries. Its namral softness is overcome by alloying it with small amounts of copper or magnesium that greatly increase its strength. It is used to make cans for food and drinks, in pyrotechnics, for protective coatings, to resist corrosion, to manufacmre die-cast auto engine blocks and parts, for home cooking utensils and foil, for incendiary bombs, and for all types of alloys with other metals. 

Recently, Sharma [299], at General Motors, proposed a low cost method for the production of Al-Mg alloys, which can be used in the automobile industry and for desulfurization of steel. The unit cell is shown in Figure 29. The cathode of liquid aluminum is at the bottom of the cell where magnesium is deposited. The electrolyte is a mixture of molten chlorides in which partly dehydrated MgCl2 is dissolved and the electrolysis temperature is 750°C. The same author also described another method to produce magnesium metal using an electrochemical cell with bipolar electrodes, shown in Figure 30. 

Magnesium occurs widely in carbonate ores, but most Mg comes from salt brines and from the sea (Figure 22-5). Sea water is 0.13% Mg by mass. Because of its low density (1.74 g/cm ), Mg is used in lightweight structural alloys for such items as automobile and aircraft parts. 

In the presence of O2, magnesium metal is protected by a thin coating of water-insoluble MgO. Thus, even though Mg is high in the activity series (Section 4.4), it Can be incorporated into lightweight stmctural alloys used in, for example, automobile wheels. The heavier alkaline earth metals (Ca, Sr, and Ba) are even more reactive toward nonmetals than is magnesium. 

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