Influence of manganese on the microstructure of secondary alloys Al-Si-Mg

The paper determines the influence of presence of various manganese content (0.2; 0.4 and 0.6 wt%) on the course of the crystallisation process, mechanical properties and structure of alloy AlSi10Mg. Recycled secondary materials with elevated content of iron were used to prepare the cast of this silumin. It was found that about 0.6 wt% of Mn causes the disappearance of the adverse, brittle phase β-Al5FeSi in favour of phase α-Al15(FeMn)3Si2, which crystallises in the form of evenly distributed in the metallic matrix of solution α (Al) with concentrated precipitations sized approximately 7-8 µm. The change of the adverse morphology of brittle eutectics containing Fe causes a slight increase of mechanical properties without the decrease of plasticity of alloys Al-Si-Mg-Mn used mainly as gravity die casting or pressure die casting. Manganese is therefore a “morphological corrector” of phase β in favour of privileged precipitations of α-Al15(FeMn)3Si2. Taking into account the economic aspects and ecological conditions it seems reasonable to apply manganese in order to increase the presence of secondary Al alloys rather than the primary elements.