EFFECT OF THERMAL EXPOSURE ON HIGH TEMPERATURE MECHANICAL PROPERTIES OF SECONDARY AlSi7Cu3Mg ALLOYS

摘要

A large number of automotive components such as cylinder heads, pistons and engine blocks are generally made by Aluminium-Silicon foundry alloys, which show a suitable combination of excellent castability, low weight, corrosion resistance and good mechanical properties. Due to the extreme working conditions, the aforementioned components can locally reach high temperature up to 300°C. However, the degradation in the mechanical properties of Al-Si alloys occurs generally at temperatures close to 200°C. The secondary Al process requires low energy consumption if compared to primary Al production with consequences both on greenhouse gases emissions and costs. For this reason, secondary Al alloys are increasingly being used, but the presence of impurities and small amounts of undesired elements has deleterious effects on the mechanical properties. Al foundry alloys are usually heat-treated to improve mechanical properties due to precipitation hardening. Among all, the T7 heat treatment (over-aged condition) is one of the most common for engine parts. The presence of incoherent precipitates decreases strength, but guarantees greater ductility and stability of the mechanical properties during high temperature exposure. The aim of this work is to evaluate the effect of thermal exposure on high temperature mechanical properties of secondary AlSi_7Cu_3Mg foundry alloys by means of hardness measurements and microstructural investigations.