Materials for consideration and use in automotive body structures

This chapter discusses the choice of materials suitable for body manufacture and provides an understanding of salient manufacturing processes, product parameters, and associated terminology. The situation has advanced significantly from the days when "mild steel sheet" was the universal answer to most body parts applications. The metallurgy of both steel and aluminum alloys has now advanced significantly, offering a wide choice of mechanical and physical properties together with other attributes. Steel is still the predominant material used for manufacture, and the generally high ratings levels shown under the "Ease of manufacturing" column reflect the provision already made by the industry for compatible facilities. The historical rule-of-thumb when considering structures or subassemblies equivalent to steel is that the weight can be approximately halved but the cost is doubled. Aluminum is the most prolific metal comprising the earth's crust (8% as opposed to 5% for iron) but has only in the last 100 years been smelted industrially, the Hall-Heroult process being used to extract the metal from alumina dissolved in molten cryolite (a fluoride of sodium and aluminum) by electrolysis using carbon anodes. Magnesium is the lightest of all the engineering metals, having a density of only 1.74 g/m 3 . It is 35% lighter than aluminum and more than four times lighter than steel. Polymers used for autobody applications may be split into thermoplastics and thermosets. Thermoplastics are high-molecular -weight materials that soften or melt on the application of heat.