Applications of aluminum alloys

8.7.2 Applications of aluminum alloys

With the need for fuel economy and weight saving, aluminum alloys are increasingly used in cars, and its two most important properties are density and thermal conductivity. Over the past 15 years the aluminum content of cars has increased from around 5% to 13% by both volume and weight. In engines they are used for pistons, cylinder heads and sumps. Al–Si casting alloys of the 3XX.X series are being used for engine blocks and Al–Si pistons with cast iron cylinder liners for wear resistance.

The superior thermal conductivity reduces the volume of coolant in the system. Aluminum wheels, vacuum cast or forged, are replacing conventional steel wheels in sports cars. Heat-treatable 4 2XXX and 6XXX as well as 5XXX series can be used for body sheet. However, the modulus of aluminum is only one-third that of steel and hence significant design changes are necessary to maintain rigidity and stiffness. A straightforward increase in gauge thickness would lead to a doubling cost, which limits the replacement to ‘quality’ cars. For bulk market cars, gauge-for-gauge substitution for steel is a future objective with structural reinforcement to enhance body torsional characteristics. This is possible with the use of adhesives in a weld-bonding approach which can reduce the weight by half,

and fuel consumption and CO 2 emission by almost 15%. Aluminum-structured vehicle technology (ASVT) is likely to be essential when emission control to reduce global warming effects is tightened. The Honda NSX all-aluminum car 5 is manufactured with conventional design and assembly, and

has three different 6000 series alloys for external panels and a structural subframe of 5182 alloy.

In aircraft construction use is made of the high strength–density ratio of the Al–Cu (2000 series) and Al–Zn–Mg (7000 series) alloys in extruded form for wing spars, fuselage and landing gear, and for the skin in plate or sheet form; typically 7075 (5.6Zn–2.5Mg–1.6Cu) is used in the T6 condition and 2024 (4.4Cu–1.5Mg–0.6Mn) in the T3 or T8 conditions. The alloys of the 7000 series have higher strength than the 2000 alloys but lower resistance to fracture. However, higher purity levels (e.g. 2124 alloy) give enhanced toughness. Alloys of both series lose strength above 100 ◦

C and are thus not suitable for supersonic aircraft. The RR58 alloy used for the Concorde at temperatures up to 175 ◦ C was originally an early engine material, for compressor blades and impellers.

Aluminum is used extensively in the construction industry because of its light weight, resistance to atmospheric attack and surface finish. For decorative applications, dyed anodic films produce a permanent durable finish. Generally, the Al–Mg–Si 6000 series is used, i.e. 6063 medium-strength and 6082 higher-strength alloys in the T6 condition for extrusions or T4 where forming is required during fabrication. The Al–Cu (2014A) alloy is also used for heavily loaded primary structures.

The packaging industry also provides a large market for aluminum alloys. The main requirement is for low-cost, simple alloys capable of being formed, and the Al–Mg (5000) series is often used. Impurity control is essential and liquid metal filtering is necessary in the production of thin sheet.

In the electrical industry, electrical conductivity grade aluminum and higher-strength 5000 and 6000 series alloys are used for transmission lines, replacing the more expensive copper. Dispersion- strengthened alloys containing a fine dislocation substructure stabilized by small precipitates are used for electrical wiring.