Experimental study of the effect of the simultaneous treatment of the melt with different currents on the quality indicators of castings

Abstract

The purpose of the work is to obtain results that would confirm the effectiveness and perspective of using the method of simultaneous treatment of a liquid alloy based on Al with different types of currents in foundry technologies. As it is known the different types of current passing through the melt (alternating, constant, pulsed) are differ from each other by their different functional capabilities. The each types of currents generate electromagnetic fields with different amplitude-frequency characteristics and distribution, which determine the sphere of influence. The work proposed to use an innovative principle of simultaneous passing of at least two currents with different electrical characteristics through the melt and with different variants of electrode systems. This method made it possible to affect more effectively on the structure and properties of the melt and, in turn, improve the service characteristics of the casting. In the work, two series of experiments were performed with the application of melt treatment with three types of currents and three types of electrode systems in different combinations. Ingot alloys of the Al-Si system was treated: AK7 (GOST 1583-93), chemical composition: Si (7.3 %); Fe (0.5 %); Cu (0.5 %); Mn (0.07 %); Mg (0.07 %); Zn (0.2 %); Pb (0.01 %), Al base; and non-standard pre-eutectic silumin additionally doped with certain components (Si (8 %); Fe (0.79 %); Cu (1.98 %); Mn (0.1 %); Mg (0.27 %); Zn (0.44 %), Al base). In contrast to the treatment of one type of current, an increase the mechanical properties of castings and an effective modification of the elements of the solid state structure were achieved. Thus, for the first grade of alloy, σВ was increased by 13 %, and δ — by 1.5 times. Also after simultaneous treatment with different types of currents with defined modes, the value of Ψ was recorded at the level of 4.4 %. For the AK7 alloy, this indicator is not even specified by the standard. For the second grade of alloy, after simultaneous treatment with different types of currents, significant grinding of intermetallics to sizes from 8 μm to 11 μm was observed, while compared to the original sample, there is practically no segregation of the intermetallic component by size. The structure of the treated samples is distinguished by the grinding of silicon particles in the eutectic. The total energy consumption, under certain conditions, for both brands of alloys was reduced by 3 times. The main mechanism of a positive change in the crystallization ability of the melt is formation of electromagnetic fields superposition with more powerful thermoforce effect in the treatment object by passing different types of currents simultaneously than when using one type of current.