Application of T6 Heat Treatment on the AlSi9Cu3 (Fe) Casting Alloy and the Effect of Copper Content

AlSi9Cu3 (Fe) foundry alloy is commonly used to produce components by High Pressure Die Casting (HPDC) for automotive and electrical industries. Mostly for cost reasons, the Cu content is held at the minimum of the compositional range foreseen by the standards. The strength of the metal is then quite low and therefore the components are used only in low or non-stressed applications. The experimental results of the present paper show that in the as cast temper, the percentage of Cu has little effect on strength. It is suggested that alternative alloys for HPDC with lower or no Cu content be adopted for non-stressed components. In the last 15 years, it has been demonstrated that Al-Si-Cu alloys for HPDC may successfully heat-treated by unconventional T6 without causing surface blistering or dimensional instability. Despite the new opportunities, there have been few industrial applications. Instead, the present authors believe possible new technological outcomes for unconventional T6, and have therefore experimented with the AlSi9Cu3 (Fe) alloy with different Cu contents. By using SEM-EDX microanalysis to get Cu composition maps in the alloy microstructure, a T6 heat treatment with lower solubilization temperature and shorter soaking time to avoiding blistering has been identified. Tensile test confirmed the effectiveness of unconventional T6 and showed a strong increase in the elastic limit of the material. The results also show that the best effect is obtained by increasing the Cu content as much as possible. It is therefore possible to produce components for highly stressed structural applications in T6 treated AlSi9Cu3 (Fe) alloy.