Aluminum casting alloys are widely used for various machine parts for the purpose of weight reduction and energy saving. Because of the strong demands for high-stiffness Al alloy to improve their operating accuracy in the fields of precision machinery and robots, we have developed Al-12.5～14%Si-5～6%Ni-14～15%Cu-0.5%Mg alloys with a stiffness of 100GPa. The solidification sequence of this alloy was investigated to clarify the structural constituents that contribute to its higher stiffness. A series of quenched Al-14%Si-5.5%Ni-15%Cu-0.5%Mg samples were analyzed by optical microscope, EPMA and X-ray diffraction. The results revealed that the alloy solidifies in the order of primary Si, primary-like Ni₂Al₃, Al (α) ＋ Si eutectic, Al (α) ＋ Ni₂Al₃ eutectic, Al (α) ＋ CuAl₂ eutectic and Al (α) ＋ Al₄Cu₂Mg₇Si₈ eutectic. Just after the crystallization of primary-like Ni₂Al₃, Al (α) hollow and α-dendrites developed around primary Si and Ni₂Al₃, since these primaries hardly nucleated the above eutectics. The thermodynamic calculation software used provides information on the solidification temperatures and volume fraction for primary Si, Ni₂Al₃, and other eutectic structures. However, it is unable to predict the appearance of Al (α) hollow and α-dendrites because these are non-equilibrium phenomena. In addition, some discrepancies were observed especially in the final stage of solidification. The evaluation performed by the thermodynamic calculation software using the Scheil's equation provides details on the final solidification reactions similar to experiment findings.

  Since the mold material and surface roughness of molds are generally influenced by the molten metal flowability, investigations into the influence of interface conditions between the molten metal and mold on the molten metal flowability should be useful for preventing casting defects caused by unsuitable mold filling behavior.

  In this study, the relationship between the interface conditions and molten aluminum alloy flowability was investigated from experimental and casting CAE results. In experiments conducted on gravity casting of aluminum alloy using a green sand mold and a die with having the same casting plan, flow stagnation was observed with the die. The simulation results showed that the stagnation was not due to heat removal. On the other hand, in the experiments on molten metal drop on the mold, the flow behavior was investigated by changing the surface roughness of the die. The influence of the surface roughness (Ra ＝ 2.3, 1.7, 1.4μm) of the die on the fluidity was not significant. Comparing the flow behavior between the sand mold and the die, the flow front of molten metal using the sand mold was advanced to the same extent as in the case of the metal mold. The cause may be due to the influence of the molten metal skin. It will be necessary to introduce some kind of algorithms for the generation of the molten metal film, wettability, oxide film, etc. regarding the fluidity of the molten metal into the casting CAE in the future.

  The effect of contained elements on the electrical conductivity of aluminum and aluminum alloys with various chemical compositions were investigated through electrical conductivity measurement and multiple regression analysis. It was found that the electrical resistivity of aluminum and aluminum alloys can be formulated with a linear multiple regression equation by taking the contents of elements as the explanatory variables and the resistivity of high purity aluminum as the intercept. For high purity aluminum with electrical conductivities higher than 55%IACS, the above equation did not have sufficient prediction accuracy. Thus, an improved equation was obtained by the same linear regression analysis. The regression coefficients in the improved equation more or less agreed with the change rates of the electrical resistivity per unit content in the solid solution state for magnesium, silicon, titanium and vanadium and in precipitation (crystallization) state for copper, iron and nickel. This suggests that these regression coefficients reflect the states of the containing elements, indicating that the linear multiple regression between the electrical resistivities and chemical compositions of aluminum and aluminum alloys is an effective means of estimating the solid solution and/or precipitation state of the contained elements as well as the electrical conductivity.