Skorobagatko I. Influence of thermal & forced processing with using of electromagnetic action on structure and properties of Al-Si alloys

In the thesis, there is further development of concepts of thermal & forced processing of liquid Al-Si alloys in the original magnetodynamic installations (MDI) with using of energy of electromagnetic fields and turbulent flows (TFP). It provides the elimination of unwanted metallurgical heredity, substantial refinement of structural components of alloys, and increasing of their plastic properties, especially elongation. There are ascertained the rational modes of TFP of hypo- and hypereutectic silumins in the MDI. Application of such modes promotes forming of dispersed and homogeneous structure of solid metal in comparison with conventional reagent treatment of melts. Due to TFP, the sizes of grains and parts of eutectic silicon are decreased in 3 times, and the sizes of silicon primary crystals are reduced in 3.5 times. As a result, elongation of the Al-Si alloys (after T6 heat treatment and special stepwise heat treatment developed in the G.V. Kurdyumov Institute of Metal Physics NASU) is raised up in 2-3 times. Effect of physical modifying of silumins is kept during a few hours. The additional refinement of structure of hypoeutectic Al-Si alloy prepared at the MDI can be realized by cooling of melt in the fore-solidifying period at its electromagnetic pouring into chill mould through the water-cooled metal duct. Subsequent intensive plastic deformation (performed at O.O. Galkin Dоnetsk Institute for Physics and Engineering NASU) provides refinement of structural components (sizes of eutectic silicon particles in hypoeutectic alloy make 0.6-0.8 micrometer, and the same ones in hypereutectic alloy make to 1 micrometer). At that, dendritic segregation in hypoeutectic Al-Si alloy is eliminated. Hardness of hypoeutectic silumin is raised up in 2 times, and the same one for hypereutectic Al-Si alloy increases in 1.45 times. Also, there is further development of concepts of thermal & forced processing of aluminium melt (AK7 silumin) in the channels of the MDI during initiation of the controlled cyclic pinch-effect. It is accompanied by pressure fluctuations of two types (with frequency of 100 Hz & amplitude of 2-2.5 kPa and with frequency of 2.5-3 Hz & amplitude of 7-10 kPa), local overheating of melt (up to 3000 K), and forming of underpressure area (to 10-12 kPa). Already after 15 min of such processing, content of hydrogen in the alloy reduces in 3-5 times, and the sizes of structural components of alloy (including intermetallides) decrease in 2-3 times. Efficiency of the developed method for TFP of hypo- and hypereutectic Al-Si alloys in the MDI is confirmed by successful experimental-industrial tests, performed both domestic and foreign specialists and enterprises, in particular, by State self-supporting factory "Almazinstrument" NASU and Korea Institute of Materials Science (KIMS).