Aluminium alloys used in bodywork

The choice of material and the condition in which it is required must depend largely upon design requirements and the manufacturing processes within the factory. The alloys most commonly used in vehicle body work are as shown in Table 4.9.

Alloy 5154A is suitable for use in car panels which are to be pressed into shape; it is supplied in either annealed condition or H2 condition,which are the most suitable for press work on vehicle bodies. Of the other materials,1200 is a commercial purity sheet,and is widely used for exterior and interior panelling where no great strength is required. Types 3103,5251,5154A and 5056A are non-heat-treatable alloys of the aluminium-magnesium range with a strength of 90–325N/mm2. They come in sheet form,and provide a range of mechanical properties to suit different applications. They are used extensively in panel work,and also for forming,pressing and machining,and can be welded without much difficulty. The plate material 5083 is a medium-strength non-heat-treatable alloy particularly suitable for welding. It can be used for parts carrying fairly high stress loads and is often used in the form of patterned tread plate for floor sections.

For internal structure members which need to be stronger than the outer panels,the heat-treatable alloys usually used are 6063 and 6082,and in oddcases 2014A. Type 6082 is a heat-treatable medium-strength alloy which combines good mechanical properties with high corrosion resistance. Permissible stresses in this alloy can be as high as 200N/mm2 under static loading conditions,although some reduction below this would normally be made for transport applications where there is a considerable element of dynamic loading. The alloy is weldable by the inert gas arc process,but there is a considerable loss of strength near the weld owing to the annealing effect of the welding process. Type 6063 is also a heat-treatable alloy but of somewhat lower strength,and is used mainly in applications requiring good surface finish or where the parts are required to be anodized.

Alloy 2014A contains a greater percentage of copper than the others,is more expensive,is more difficult to form and is less resistant to corrosion,but has the advantage of a greater tensile strength.
Fastenings and solid rivets can be of commercial purity material or of aluminium alloy 5154A,and for smaller sizes 6082 is sometimes used. Rivets are also available in 5056A material,but should not be used in cases where high temperatures occur in service. Bolts used in bodywork are normally of the 6082 alloy.
The condition in which heat-treatable alloys are supplied should be related to their application oruse in bodywork. For example,if a section is to remain straight and is part of a framework which is to be bolted,riveted or welded in place,it is obvi- ous that the material used should already be fully heat treated so that maximum strength is provided to support the framework or structure of the body. On the other hand,if the section has to be shaped, bent or formed in any way the material should be used in the annealed condition and then heat treated after the shaping operations have all been carried out.
Aluminium alloys are now being accepted by the automobile manufacturers as a standard materialfor exterior and interior trim,and are used for all normal bright trim applications such as radiator grilles,headlamp bezels,wheel trim,instrument panels,body mouldings and window and wind- screen surrounds. Alloys used for trimming can be divided into two groups:high-purity alloys bright finished on one side only,in which the majority of the trim components are made; and super-purity alloys for use when maximum specular reflectivity is an advantage,such as would be required by light units.