Aluminium casting alloys AlSi10Mg and AlSi12 are frequently used in the automotive industry (in casting applications). There are both: primary as well as secondary/recycled aluminium alloys on the market, that vary in price and quality. As there are certain differences in the quality of these alloys, an analysis about the influence of quality on solidification, microstructure and mechanical properties was implemented in this research work.
The comparison of the mentioned properties took place in the as-cast state and the heat treated state. The influence of alloy quality on solidification was analyzed by simple thermal analysis and differential scanning calorimetry. The basic mechanical properties analyzed were tensile strength, yield strength, elongation and hardness. Preliminary research determined that recycled alloys have around 10–15% lower strength properties due to higher share of iron, which is challenging to avoid in secondary alloys. It forms intermetallic phases that negatively affect the mechanical properties. Microstructural differences were analyzed using an optical microscope.
AlSi10Mg and AlSi12 alloys with their derivatives made of secondary aluminium (AlSi10Mg(Fe) and AlSi12(Fe)) were compared, which contain a higher proportion of iron, which impairs mechanical properties. In alloys, its effect is compensated by manganese, which allows the formation of a more desirable, rounded Fe-phase α-Al15(Fe,Mn)3Si2 in the form of Chinese script instead of sharp β-Al5FeSi needles. In the case of the AlSi10Mg alloy, the Mn:Fe ratio has been shown to have a pronounced effect on the mechanical properties, while magnesium hardens the aluminium matrix during heat treatment, which significantly increases the mechanical properties. However, the AlSi12 alloy is not a precipitation hardenable alloy, so the mechanical properties do not improve significantly after heat treatment.
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