Higher-strength, higher-toughness die cast wheel material using recycled aluminum

In an attempt to reduce CO2 release from the alloy wheel production, we have developed such an aluminum alloy for casting that satisfies necessary property requirements using recycled aluminum and without heat treatment. The wheel is a critical safety item of the vehicle requiring higher toughness and strength. In many wheels, virgin aluminum containing small amounts of impurities are used to maintain toughness, and the heat treatment (T6), in which quick heating and cooling are conducted after the casting, is applied to provide ensure strength. At the start of this project, we focused on two wheel-manufacturing processes; the production of virgin aluminum and the heat treatment, from which a large amount of CO2 is released. The change from the virgin to the recycled material allows reduction of CO2 release to 1/9. The issue in the use of recycled material is that impurities grow in the metal structures as an intermetallic compounds and lower toughness. To deal with the said issue, we have chosen the High-Pressure Die Casting (HPDC), in which the hot material after the casting is quickly cooled and which allows dispersion of intermetallic compounds in the form of fine particles. The chemical composition, we determined the amounts of additives(Mn) for promotion of fine particles of Fe, which is one of the impurities especially easily be contained and lowers toughness. Combining with the quick cooling effect, the amounts of additives (Si and Mg) were determined to obtain the target strength without the heat treatment. With those measures taken, the wheel having the same weight as the one made of virgin aluminum has been achieved using recycled aluminum and ordinary casting equipment without the heat treatment. The elimination of heat treatment helps to improve wheel production efficiency by 15% and reduce CO2 release by 80%.