Abstract
In this study, the possibilities of the microstructure refinements effect of processing by electromagnetic and magneto-hydrodynamic means on high-strength casting aluminium alloys Al-Zn-Mg-Cu/Ni (0.2%Zr) system has been studied. In the case of direct manufacturing of high-strength casting Al-alloy by the MHD-physical affecting, the unidirectional 120Hz pulse electromagnetic force(70∼143.5N, 2.5∼3.5m/s) created in working area(WA) of the magneto-dynamic installation electromagnetic pump has provide a fine emulsion distribution of intermetallic particles in liquid melt during intensive MHD-processing for melt capacity of 150∼500kg. Microstructure of permanent chill-mold specimens (1” rod and 3” billet) has shown the unique non-dendrite microstructure with compact grains in range of 50∼100μm, and distributed homogeneity by all cross-section, instead an over 250μm dendrites for the non-treated state at sampling from conventional melting furnace.As well, applying MHD-processed alloy for low pressure casting method at manufacturing 3” billet for 550mm lengths into graphite tube have an mainly compact globular microstructure, characterized as non-dendrite state with 80∼120μm grain size and 50∼80μm in the central part of billet. Achieved effect can be explained by an artificial heat-force effect of the pulse unidirected electromagnetic force, created in the MDI working area which affecting the solidification structure. In addition just 10 minutes for 150kg alloy by artificial pumping mode MHD melt processing was found to increase cast-ability of the Al-Zn-Mg-Cu casting high-strength alloy at pouring temperature of 680∼720°C, wherein hot-cracks disappear, and hot-cracks effect is not occurs for the different conditions of the pouring speed.Tensile stress test of the developed high-strength casting Al-Zn-Mg-Cu alloys has been shown 547∼566MPa, 516∼547 yield stress and 2.9-3.4°% elongation for the case of chill mold gravity casting.
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