Effect of Al5TiB Master Alloy with P on Microstructure and Mechanical Properties of AlSi7Mg Alloy

Aluminum-silicon alloys are popular casting alloys. In its raw state, the microstructure of the hypoeutectic silumin consists of a large eutectic β phase against the background of dendritic eutectic α. Due to its large microstructure components, mainly the eutectic β phase, this alloy has low mechanical properties. The unfavorable properties of hypoeutectic silumin can be improved by changing the size and shape of the alloy’s microstructure components. There are several possibilities for controlling the microstructure and the resulting mechanical properties of the alloy. One possibility is to modify the alloy with elements and chemical compounds. This paper presents the effect of phosphorus with Al-Ti-B on the microstructure and mechanical properties of hypoeutectic silumin AlSi7Mg. The proportions of Ti to B were selected on the basis of the results presented in the literature, recognizing the optimal ratio of 5:1. The modifier was introduced into the alloy in the form of an AlTiBP master alloy with a variable content of titanium, boron, and phosphorus. Phosphorus was added at the levels of 0.1, 0.2, and 0.3% of the weight of the modified casting. As a result of the tests carried out, the modifying effect of the introduced master alloy was confirmed. A different morphology of microstructures was obtained for the different chemical compositions of the modifier. The most favorable modification effect, whose measurable parameter is the highest (out of the obtained) mechanical properties, was found for the modifier containing 0.25% Ti + 0.03% B + 0.2% P. It was also found that phosphorus, in the presence of titanium and boron, affects the microstructure and mechanical properties of hypoeutectic silumin AlSi7Mg.