Abstract
The most commonly used elements to modify primary silicon crystals in the structure of hypereutectic aluminum-silicon alloys are phosphorus and sulfur. Phosphorus has been shown to have the highest coefficient of modification with respect to the primary silicon and is therefore a preferred modifier. There are also data on the positive effect of the modifiers Sb, Sr, Ti, and B on the silicon crystals in the structure of this type of alloys. The influence of the modifiers phosphorus, strontium, titanium and combinations of them on the size and shape of both the primary silicon crystals and the silicon crystals in the composition of the eutectic of the AlSi25 alloy has been studied in this work. Mechanical tests have been performed to determine both the strength and the plastic parameters of the investigated alloy (in unmodified and modified state). The classic for this type of alloys modifier - phosphorus - has been introduced into the melt by the ligature CuP10. Strontium has been introduced by the ligature AlSr10, and titanium - by the ligature AlTi5B1, the two ligatures in the form of rods. The investigated alloy has also been modified by combinations of the used modifiers: phosphorus and strontium, phosphorus and titanium.The influence of the used modifiers on the structure and mechanical properties of AlSi25 alloy has been discussed.
Highlights
Modification is a process of metallurgical processing of the melt, in which by introducing small amounts of special additives - modifiers [1], the structure of the aluminumsilicon alloys changes unnaturally.According to the generally accepted classification of P.A
The main amount of primary silicon crystals in the structure of the unmodified AlSi25 alloy are irregular in shape and large in size - 190μm
After modification of the alloy with phosphorus in the amount of 0.04 wt%, refinement of the primary silicon crystals in the structure of the alloy is observed, they are regular in shape, evenly distributed in the structure of the studied alloy and measure in the range of 25-55μm
Summary
Modification is a process of metallurgical processing of the melt, in which by introducing small amounts of special additives - modifiers [1], the structure of the aluminumsilicon alloys changes unnaturally. According to the generally accepted classification of P.A. Rehbinder [2], the modifiers are divided into two groups. Type I modifiers are surfactants, adsorbed on the crystalline germs and reducing the growth rate of the solid phase. Type II modifiers are usually refractory substances with a crystal lattice, identical in appearance and with parameters close to those of the crystallizing alloy. For higher efficiency it is desirable that the particles have a maximum size of less than 5 μm. Distributed in the melt in a finely dispersed to colloidal-dispersed state, they become independent centers of crystallization or form such centers as a result of the interaction with the melt
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