RESISTOMETRIC STUDIES OF STRUCTURAL TRANSFORMATIONS IN MELTS OF AL–SI SYSTEM

Procesi littâ, 2023, Vol 4 (154), 28-35

Abstract

The results of previous thermodynamic calculations do not exclude the possibility of temperature-induced changes in Al–Si system melts structure. It was also established previously that the tendency of this system melts to structure change when temperature is changed should be most clearly detected in the hipereutectic alloys. In this paper, an attempt was made to experimentally evaluate the possibility of Al–Si system melts structure changing by means studying the temperature dependence of such a structure-sensitive property as electrical resistance, as well as to establish temperature limits in which the structure of the specified melt remains stable; using analysis of components ions outer electron shells structure, the possible structures of melt microregions were characterized in the temperature intervals that correspond to the characteristic segments of electrical resistance polytherm. The electrical resistance polytherm of hipereutectic aluminum-silicon alloy containing 17,6 wt. % (17,1 at. %) of silicon has been investigated in temperature range from 650 ^oC (slightly higher than the liquidus temperature) to almost 1150 ^oC with a step of 15 ^oC. Electrical resistance was determined by the voltmeter-ampermeter method with a four-probe connection scheme. It was established that the electrical resistance polytherm of investigated alloy has a non-monotonic character. The presence of inflections on electrical resistance temperature dependence curve at temperatures approximately 750 ^oС, 820 ^oС and 950 ^oС allows conclude about possibility of temperature-induced changes in Al – Si system melts structure. It can be assumed that at temperatures that slightly exceed the liquidus temperature, the structure of the melt is similar to structure of an emulsion. At these temperatures, the melt is formed by two types of groups: groups formed mainly by aluminum atoms with a metallic type of bond, and groups formed by silicon atoms with a predominant covalent bond. With a further increasing of temperature, covalent bonds are destroyed, silicon atoms are ionized to a metallic state, and the melt gradually transit to a truly homogeneous state.