AlSi7Mg alloy is a heat treatment alloy that is subjected to artificial aging to achieve higher strength. The casting of this alloy takes place in a relatively narrow temperature range, which is determined by the composition of the melt, the wall thickness of the casting, as well as the size and weight of the casting. If the casting temperature is lower than optimal, the cavity of the mould does not fill up; the thin walls solidified too quickly, which in turn leads to disruptions of the process, porosity, and poor casting surface. High casting temperature causes shrinkage during solidification and consequent loss of dimensional accuracy. The high temperature also prolongs the solidification time, thus reducing productivity.
As part of the master's thesis, we simulated the technological path of preparation of the melt of the AlSi7Mg alloy at the laboratory level. The aim of the master's thesis was to determine the optimal conditions for melt preparation and the most suitable range of pouring temperatures. In the experimental part, the melt was overheated and poured at different temperatures. During solidification, a cooling curve was observed in two different measuring cells. We performed a thermodynamic calculation using Thermo-Calc software. The castings were cut and samples were prepared for chemical analysis, DSC analysis, metallographic and mechanical testing.
In the chemical analysis, there were no significant changes between the individual samples, so the course of solidification of the samples cast into the same cells is similar. The characteristic temperatures, reaction enthalpy and microstructure are also comparable between the samples. Differences occur in the cooling rate between samples cast into cells made in the Croning process and samples cast into steel cells, where the microstructure is finer due to higher cooling rates. From thermodynamic calculations and microstructures recorded by scanning electron microscopy and EDS analysis, it is assumed that there are the primary α-Al crystals and eutectic phases β-Si, Al18Fe2Mg7Si10, Mg2Si, Al9Fe2Si2, and Al3Ti in the microstructure. The results of yield strength, tensile strength, elongation and toughness do not differ significantly between the samples, and the results indicate that the most appropriate casting temperature is in the range from 730 to 750 ⁰C.
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