History of Aluminum
Washington Monument’s 1884 cap was the 1st application to use cast aluminum in design.
How Aluminum is Produced
Aluminum materials used in castings come from recycled parts or bauxite mining operations.
The Automotive sector is the largest commercial segment for aluminum castings.
Aluminum Casting Processes
Description of the most common casting processes for Aluminum alloys
Image Credit: Encyclopedia Britannica, Inc. https://www.britannica.com/science/aluminum
Pure aluminum is quite soft and weak, consequently not very useful for most castings. Commercial aluminum materials alloyed with specific amounts of other metallic elements (Si, Mg, Fe, Cu, etc.) can be improved by hardening, strengthening and forming. With low-alloy forms of aluminum being ductile and highly malleable, the material can be drawn into wire or rolled into thin foil. Even in th alloyed form, aluminum material is only about one-third as dense as iron or copper, making it a value to aerospace, automotive and general consumer products. Though chemically active, pure aluminum is corrosion-resistant, because in air a hard, tough oxide film forms on its surface. Corrosion resistance in reactive environments is greatly improved with plating, painting or elastomeric coatings.
Aluminum is an excellent conductor of heat and electricity. Its thermal conductivity is about one-half that of copper, and the electrical conductivity is about 61% by cross-sectional area. However, with the lower density of aluminum wire, it is twice as conductive by mass. As aluminum is roughly one-third the cost of copper by weight, the economic advantages are considerable when large conductors are required.
Aluminum is the most frequently used material for aluminum castings to produce light weight parts.
Aluminum Alloys for Casting
The 300 series is generally classified as an Aluminum-Silicon alloy grade, which probably accounts for 90% of the production aluminum castings. Most aluminum wheels, steering knuckles, control arms and cylinder heads use the A356 alloy, as do many cylinder block designs. The A356 alloy is cast in both sand and permanent mold processes, with the metal being introduced using gravity or assistance with low pressure gases.
For High Pressure Die Casting with Aluminum alloy materials, the most common materials follow an industry standard that has been in place for about 70 years: A380-series alloys. In particular, the 380 and 383 compositions were formulated specifically for use with High Pressure Die Casting. These alloys provide benefits related to:
- Die Erosion – Elevated Fe and Mn helps to minimize amount of erosion found on dies.
- Molten Fluidity – Elevated Si helps to improve the fluidity of the aluminum as it fills the cavity.
- Hot Strength – Elevated Si, Cu and Mg help to provide resistance to tearing during mold removal.
- High Strength – The as-cast condition of common HPDC alloy is high enough to avoid heat treating.
- Wear Resistance – The Si additions help to provide hardness and wear resistance on friction surfaces.