Innovative chemical grain refinement of secondary Al foundry alloys

The aim of this thesis is to understand the effectiveness of AlTi3C0.3 master alloy as innovative grain refiner for secondary Al foundry alloys, in replacement of master alloys based on Al-Ti-B system because of their drawbacks. The Al alloy involved in this work is EN 42000 which is a secondary Al alloy that belongs to AlSi7Mg category. The first part of the experimental work involves the metallographic analyses of samples extracted from three car wheels which the chemical grain refinement was obtained by using AlTi5B1, AlTi3C0.3, and a mix of both, respectively. The results show that AlTi3C0.3 master alloy can be an acceptable replacement for AlTi5B1. The second part is dedicated to find the optimal addition level of AlTi3C0.3 by casting samples in the laboratory with different amount of grain refiner, considering casting temperatures of 750 °C and 700°C, and three different cooling rates. Metallographic analyses show how the effectiveness of grain refiner is in general remarkable for high contents but affected by the casting temperature. A further investigation was conducted for a possible poisoning effect which was confirmed for both casting temperatures within the first minutes after the addition of grain refiner.