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Abstract

The effect of combination grain refinement with AlTi5B1 master (55 ppm) and Sr-modification with AlSr5 master (20, 30, 40, 50 and 60 ppm) on the microstructure, tensile and hardness properties of AlSi7MgTi cast alloy were systematically investigated. Eutectic silicon was studied by optical and scanning electron microscopy after standard (0.5% HF) and deep etching (HCl). Morphology of eutectic Si changes from compact plate-like (as-cast state) to fibbers (after modification). Si-fibbers in samples with 50 and 60 ppm Sr coarsen probably as a result of over-modification. The optimum mechanical properties has the experimental material which was grain refined and modified with 40 ppm of Sr (UTS = 220.6 MPa; ductility = 6.1%, and 82.3 HBW 5/250/15).
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Abstract

In Al-Si alloy the iron is the most common impurity and with presence of other elements in alloy creates the intermetallic compounds, which decreases mechanical properties and increases of porosity. The cause of the negative effect of intermetallic particles on the mechanical properties is that it is more easily break off the tension load as the aluminium matrix or small particles of silicon. By adding suitable alloying elements, also known as iron correctors, is possible to reduce this harmful effect. In the article is evaluated influence of manganese on microstructure with performed EDX analysis selected intermetallic phases and tensile test and measurement of length of Al5FeSi phase. For realization experiments was used AlSi7Mg0.3 alloy with increased iron content. Manganese was added in the amount 0.3 wt. %, 0.6 wt. %, 0.8 wt.% and 1,2 wt. %. From performed measurements it has been concluded, that increased amount of manganese, i.e. Mn/Fe ratio, does not have significant influence on mechanical properties AlSi7Mg0.3 alloy in the melted state.
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