In an attempt to reduce CO2 release from alloy wheel production, we have developed an aluminum alloy for casting that satisfies necessary property requirements using recycled aluminum, but without heat treatment. The wheel is a critical safety feature of any vehicle, and it should have toughness and strength .In many wheels, virgin aluminum containing small amounts of impurities is used to maintain toughness, and heat treatment (T6), which is post-casting quick heating and quenching, is applied to provide strength.
At the start of this project, we focused on two wheel-manufacturing processes, production of virgin aluminum and heat treatment, from which a large amount of CO2 is released. By switching to recycled aluminum, CO2 was reduced to one-ninth the original amount.
The issue with recycled material is that impurities grow in the metal structures as intermetallic compounds and this reduces toughness. To deal with this issue, we have chosen high-pressure die casting (HPDC), in which the hot material after the casting is quenched to allow dispersion of intermetallic compounds in the form of fine particles. As for the chemical composition, we determined the amounts of additives (Mn) that facilitated fine particles of Fe, which is a common impurity that lowers toughness.
Combining with the quenching effect, the amounts of additives (Si and Mg) were determined to obtain the target strength without heat treatment.
With this process, we achieved a wheel using recycled aluminum and ordinary casting equipment without heat treatment that is the same weight as one made of virgin aluminum. The elimination of heat treatment helps to enhance wheel production efficiency by 15% and reduce CO2 release by 80%.