Die-cast and high-speed twin-roll cast products were fabricated using an ADC12 alloy. Tear specimens were prepared from these cast plates for tear test and microstructure observation. The tear toughness was evaluated by using both UE_p and log σ_max－log λ chart. The microstructure of ADC12 alloy consisted of primary α-Al dendrites, dispersed eutectic Si particles and other secondary particles. Si particles in the die-cast product were coarse and plate-like. In contrast, they were fine and globular in the roll-cast product. The calculated UE_p value of the roll cast product was six times larger than that of the die-cast product. The fracture surface of the die-cast product was relatively flat and the cleavage fracture of Si particles was clearly observed. On the other hand, for the roll-cast product, fine dimples covered the fracture surface and tear lips were also observed on the fracture surface. Difference in fracture mode, brittle and ductile, was considered to be due to a large difference in the morphology of Si particles, which occurred by rapid cooling in the roll casting process compared to the die-casting process. Refinement of the solidification structure is effective for improving the toughness of brittle cast products, such as ADC12 alloy.

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  In (Fe, Ni)-Cr-C alloys which are substituted by 25massNi% to 70mass%Ni for Fe in high chromium cast irons, the effect of Ni content on the solidification structure, solidification sequence and liquidus surface diagram was investigated.
  It was found that the microstructures of alloys consist of matrix and M₇C₃ carbides precipitated as primary and/or eutectic crystals, and that they are similar to general high chromium cast irons except for mostly austenitic matrix. According to the EDS analysis of alloy content in each phase of the specimens, Cr content in M₇C₃ carbide increases by increasing the Ni content but that in γ has almost no change.
  Solidification begins by crystallization of primary austenite (γ) in hypoeutectic alloy and that of primary M₇C₃ carbide in hypereutectic alloy, and is followed by the precipitation of (γ+M₇C₃) eutectic in both cases. However, graphite precipitates from melt in alloys with high C or high Ni content and its precipitation region shifts to the low C-high Cr side as Ni content increases. The (γ-M₇C₃) eutectic line on the liquidus surface diagram moves considerably to the low C side with an increase in the Ni content, but it returns to the high C side when the Ni content exceeds 50mass%. The diagrams obtained by the Thermo-Calc software are found to be close to those constructed using experimental results.

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  Multi-component white cast irons containing multiple carbide-forming elements such as Cr, Mo, W and V have been widely popularized as roll materials for hot rolling mills because of their excellent wear resistance. In this research, effects of carbon (C) and tungsten (W) contents on mechanical properties and hot wear resistance were investigated using Fe-5%Cr-5%Mo-5%V-5%Co-W-C (mass%) cast alloys. Cast irons with M₂C eutectic carbides and martensitic matrix were obtained in the range of C=1.5 to 2.5mass% and W=0 to 7.5mass%. Martensite matrixes showed over 600HV in micro-hardness, and the change in micro-hardness was closely related to that of macro-hardness. Tensile strength, compressive 0.2% proof strength and fracture toughness were high in cast irons with high hardness, but they decreased in 3mass%C cast irons due to the existence of large amount of carbides. Hot wear resistance was better in cast irons with higher hardness and higher fracture toughness.

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  In the case of aluminum, for example, iron impurities form coarse columnar intermetallic compounds during solidification, which hamper the recycling process. To control the compound morphology, a series of experiments were designed to apply ultrasonic vibration during solidification. Al-Si alloy systems with different iron contents were heated to their molten state. In the alloy systems, the primary crystals formed from the liquidus temperature were intermetallic compounds identified as Al₃Fe, α-AlSiFe (Al_7.4SiFe₂) or β-AlSiFe (Al₉Si₂Fe₂).
  In Al-6Si-4Fe, Al-12Si-4Fe and Al-18Si-4Fe alloys, coarse plate-like intermetallic compounds appeared when solidified normally, however, distinctive fine granular structure was achieved with the application of ultrasonic vibration.
  Almost all of the iron in Al-Si-Fe alloys are crystallized as intermetallic compounds. As a result, the density of the intermetallic compound became higher and showed gravitational segregation. Thus it is possible to produce castings where the intermetallic compounds are accumulated towards the bottom by gravitational segregation.

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