Current Status Of Forged Aluminum Alloy Wheels And Cast Aluminum Alloy Wheels

 A356 is a cast aluminum alloy, which is an Al-Si-Mg alloy. Because it contains a large amount of Si (content 6.5-7.5%), the A356 aluminum alloy has good fluidity and comprehensive casting properties. However, this also reduces the impact resistance of this type of aluminum alloy. Cast aluminum alloy wheels are produced from this type of aluminum-silicon-magnesium alloy. 6061 alloy is a deformed aluminum alloy, which is commonly known as a forgeable aluminum alloy. Since there is no requirement for its liquid fluidity, but relatively high requirements for its solid state deformation, its Si content is 0.4 to 0.8%. Therefore, its impact resistance is much stronger than that of A356 cast aluminum. Most forged aluminum alloy wheels are forged from 6061 alloy.

(1) Casting process of aluminum wheels

 A356 aluminum alloy melting - degassing - pouring - forming - T6 heat treatment - machining - surface treatment, etc. The process of gravity casting aluminum rims is to pour molten aluminum directly from the gate into the mold to cool and form. This casting method is simple, and the mold cost is low. However, the pouring riser is relatively large, and the aluminum material consumption is high; gas and impurities are easily involved during pouring, and the flow and temperature stability are poor. Therefore, there are many casting defects. The tilted weight casting developed on this basis can reduce these defects.

The low-pressure casting aluminum wheel process is to inject the aluminum liquid directly into the wheel rim model through the liquid riser pipe under air pressure in the aluminum liquid holding furnace under the mold. The principle is similar to that of a pneumatic hot water bottle. In this way, the temperature and speed are stable, and gas and impurities will not be brought into the mold. Therefore, there are fewer casting defects. Since there are almost no pouring risers, aluminum material consumption is relatively small. On this basis, the development of differential pressure casting and atmosphere-protected casting can reduce casting defects to a minimum.

(2) Forging manufacturing process

6061 aluminum alloy round bar - cut into sections according to the weight of the blank - heated to about 400 degrees - preliminarily formed by forging 3 to 4 times on a forging press with a capacity of more than 8,000 tons - final cold spinning by a powerful spinning machine - T6 heat treatment - machining - surface treatment, etc. The forged aluminum alloy has a high density, refined grains, and a fibrous structure, and its mechanical properties and strengths, such as hardness, tensile strength, and yield strength, are greatly improved. At the same time, the defects of looseness, pore,s and poor impact resistance of cast aluminum alloys are avoided. Therefore, the mechanical properties of forged aluminum alloy wheels of the same specifications are about 30% higher than those of cast wheels, and the weight can be made about 20% lighter than the latter.

In addition, forged aluminum wheels contain less silicon and are denser than cast aluminum wheels. Therefore, forged aluminum wheels conduct electricity and heat better than cast aluminum wheels. Therefore, forged aluminum wheels can be perfectly colored on the surface through anodization; good thermal conductivity can reduce tire punctures and brake system losses.

(3) Process between casting and forging

Squeeze casting (also called molten forging) means applying pressure in the mold after casting to refine the grains and increase density, thereby increasing strength and reducing weight. Casting and spinning are used to cast the casting blank to stretch and squeeze the bead part of the wheel through a spinning machine, so that the grains of the bead part are refined and the density is increased, which enhances the mechanical performance and reduces the weight. There is also the so-called continuous casting and continuous forging technology invented in China in recent years. There is also semi-solid forging abroad, which has very high technical difficulty and equipment requirements.

However, these aluminum wheels are manufactured using Al-Si-Mg alloy. Mechanical properties, especially impact properties, cannot be compared with forged aluminum alloy wheels.

Since aluminum wheel hub production is a high-input, high-output industry, many companies have invested in the casting process in the aluminum wheel industry.

Cast aluminum wheels are a material-intensive, labor-intensive, low-value-added product. In addition, aluminum casting is an industry with pollution, high energy consumption, and poor working conditions for workers. Developed countries such as Europe and the United States are currently prohibiting such products. Not interested, the aluminum wheel hub industry has gradually moved to the third world and has directly purchased products.