Aluminum die casting is a metal forming process. It does not rely on gravity, but on pressure. Liquid aluminum is poured into a mold consisting of two halves. After the molten aluminum solidifies, the cast aluminum parts are separated. The die casting is obtained. At JC Casting, we have 3 main aluminum die casting methods. They are gravity die casting, pressure die casting, and sand casting.

Gravity die casting

Gravity die casting, also known as permanent mold casting, is suitable for production of different batches. Aluminum castings made by gravity die casting process may be larger than those made by die casting process. Gravity die casting aluminum parts can weigh up to 10 kg, but larger castings are sometimes considered using sand casting because of its lower production cost.

Since this casting process uses gravity to pour the metal, the pouring speed is relatively low, but the solidification speed is fast. Gravity die casting gives aluminum castings excellent mechanical properties. The castings are usually sound, provided that the alloy used has good fluidity and resistance to hot cracking.

Typically, T6 heat treatment helps to improve the mechanical properties of aluminum castings after gravity die casting process. If maximum performance is required, heat treatment includes high temperature solution treatment, followed by quenching, and then natural or artificial aging. For small castings or less important parts with very fast cooling in the mold, solution treatment and quenching can be omitted, relying on rapid cooling in the mold to retain the compounds that will produce age hardening in solution.

The most common gravity die casting aluminum alloys in China are: A356 alloy, A380 alloy, etc. It is worth mentioning that A356 aluminum alloy is the most commonly used because it is always followed by T6 heat treatment to increase its strength for applications such as ships and pumps.

Pressure casting

Pressure die casting is another aluminum casting method different from gravity die casting. This casting method is particularly suitable for mass production of relatively small aluminum parts. Pressure die casting injects molten metal into a metal mold under considerable pressure. The combination of rapid injection and rapid solidification under high pressure produces a dense, fine-grained surface structure, resulting in excellent wear and fatigue resistance.

Pressure casting can ensure the precise tolerances and good surface finish of aluminum castings, and can produce aluminum castings with small or uniform wall thickness.

Aluminum castings produced by die casting are usually not welded or heat treated because of the residual gas. Special techniques and care are required to produce pressure-resistant parts.

Typical die casting aluminum alloys are: A360, A380, etc. About 85% of aluminum die castings are made of aluminum-silicon-copper alloys such as A380. Aluminum castings of A380 alloy have good strength and corrosion resistance, as well as high fluidity and no hot brittleness required for casting. Die casting aluminum castings are mainly used in the automotive, truck and other markets.

Sand casting

Sand casting, in a broad sense, refers to the use of sand to form a mold.

The process starts with a resin model, which is a replica of the product and is filled with sand to make a hardened mold. Other sand molds (called sand cores) are placed in the mold to create an internal cavity. The molten metal is manually poured into the mold through a flow system and cooled. After being removed from the mold box, the surface of the casting is shot peened and finished.

Sand casting is fast, relatively low cost and can produce aluminium castings of varying sizes and complex geometries, but the surface finish and dimensional accuracy cannot be compared with gravity or pressure die casting methods.

Despite the relatively low initial investment, the unit cost can be much higher than the gravity die casting process. The same is true for investment casting (lost wax), which is only economical for very low-volume, prototype work.