Effects of Additives on the Fatigue and Impact Properties of Recycled Al-Si Alloy wheels

Abstract

Minor variations in alloy composition are the primary causes of casting rejects and occur even when the normal process conditions prevail. These variations impact significantly in microstructure and mechanical properties of aluminium alloy castings. Therefore, it is necessary to closely control the alloy composition and molten metal quality. Al-Si alloys are light-weight structural materials which play an important role in vehicle weight reduction and improving fuel economy in automobile industry. Currently, 85 percent of aluminium castings are used in the automobile and aerospace industry due to the unique casting properties and mechanical strength. Unfortunately however, Al-Si alloy castings are known to suffer from presence of iron that greatly undermine their mechanical properties such as impact energy and fatigue strength. Finding an innovative solution that reduces the effects of the presence of iron is an area of increased research interest. In this paper, the effects of additive elements on the impact and fatigue strength of the aluminium alloy castings from wheels were investigated. The aluminium wheels were melted in an oil fired furnace and the metal poured into 4 kg ingots. A sample was collected in a carbide crucible, quenched and used to obtain the alloy chemistry. The ingots were re-melted at 7500C and poured into a sand mold. This procedure was repeated with variations of strontium, iron and manganese elements. The castings were then machined according to ASTM-E8 standards for the impact specimen and ASTM-E466-82 for the fatigue specimens. The results depicted that Strontium addition increased both the fatigue life and impact strength of the alloy, while iron addition reduces. However, addition of manganese neutralized the detrimental effects of the iron.