Advanced Materials Research Vols. 15-17

Abstract: In the lost foam casting (LFC) of aluminum alloys, the expandable polystyrene (EPS) foam characteristics (foam composition, polymer processing and bead fusion) influence the formation of deleterious fold defects in the final casting. In this research, four types of EPS beads were investigated: (1) the regular EPS beads, (2) 2wt% hexabromocyclododecane and 2wt% dicumyl peroxide added to the EPS beads during the polymerization process, (3) 2wt% silicaalumina blended to EPS beads after the pre-expansion process of the beads and (4) 2wt% hexabromocyclododecane blended to EPS beads after the pre-expansion process of the beads. The density of the regular and modified EPS beads was kept constant at 25.63 kg/m3. Aluminum alloy A356 was poured at 1023 K into the window pattern. The window patterns with regular EPS beads did not fill completely and had identifiable carbon/oxide defects on the surface. The window patterns with the additives were completely filled with a few surface defects. From thermogravimetric analysis (TGA), it was found that the EPS beads with silica-alumina had a reduced onset temperature of degradation of EPS (from 634 K to 618 K) and a reduced activation energy (from 188 kJ/mol to 147 kJ/mol) relative to the regular beads. In the organic brominatedmodified EPS (both through blending and polymerization), it was found that the value of the preexponential (rate equation) was significantly increased. Through light optical microscopy (LOM) and scanning electron microscopy (SEM), it was found that the polymerization process additives increased the degree of bead fusion whereas the post pre-expansion additives decreased the degree of bead fusion. Finally, the EPS beads treated during the polymerization process produced castings with the least overall surface, subsurface and internal defects.

Abstract: It has been reported that scandium addition improved various properties of aluminum alloys. However, present authors can not find any reports about the addition of Sc to 6000 series alloys. In this study, Sc was added to 6061 alloy and various effects of the Sc addition on aging behavior were examined, comparing with Al-Sc binary alloy. In the STQ state, resistivity at 77K, ρD77, of 0.2%Sc added alloy (6061+Sc) was about 2.0n-m higher than the alloy of no addition (6061). The ρD77 increased in initial stage of isothermal aging up to 473K, then decreased. Though ρD77 of binary Al-0.176%Sc alloy began to decrease from 1.8Ms at 448K and 18ks at 523K, excess decrease in ρD77 of 6061+Sc corresponding to precipitation of Sc compounds was not clear. Peak value of the HV0.1 was decreased and peak aging time delayed by the Sc addition in aging up to 498K. However, softening by overaging was retarded by the Sc addition. These effects of the Sc addition are considered to come from vacancy trap by solute Sc atoms or interface between particles of Sc compound and matrix acting as vacancy sinks.

Abstract: A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.

Abstract: This study was investigated about that behavior of α phase during recrystallization process and the influence of the amount of strain on semi-solid structure of AC4C aluminum alloy which was processed by one way torsion working. AC4C aluminum alloy billets having a diameter of 35mm and a length of 400mm were torsioned by a single side torsion machine. The maximum strain (γmax) of the specimens in this experiment was 0.88. The specimens were etched for the microstructure observation by optical microscope. The casting material (γ＝0) and the torsion material (γ＝0.73) were remained dendrite structure from room temperature to 565°C. The casting materials had grain-shaped structure when they reached to 585°C which is an eutectic temperature in this alloy. However the torsion working material had it when they reached to 577°C from eutectic temperature on down. In semi-solid region, the structure of the torsion working material was finer than that of casting material and became a more grain-shaped structure. The casting material which was heated to the eutectic temperature was changed to dendrite structure again. However the torsion working material was remained grain-shaped structure.

Abstract: It makes use of that excellent nature, high purity aluminum is being used as a function material in the electron, the high technology industry and information. Generally that material is molded as a slab, and processed through such as metal rolling is given after that, and it is being made. It is increase demand that it use for condenser. Condenser capacity is increase by making a (100) oriented cube texture crystal. It is known effective to increase a solid solubility of iron to aluminum that make increase the condenser capacity. Therefore, the cooling rate of Al-10,100 and 1000ppm content Fe was controlled by single roller equipment. Research was done about the relations of the amount of solid solubility of iron to aluminum and the cooling rate. It is result that the amount of solid solubility of iron to aluminum becomes 800ppm at the cooling rate of 2×103 K/s. When the cooling rate rises, the amount of solid solubility increases. The change appears in the separation thing as well because the amount of iron changes by this when the cooling rate is high. When iron is solid solubled in aluminum, it is bigger than the case of solid solubility formed by other general metal elements. Hardness is four times rose more than pure aluminum by solid solubility of iron to aluminum about 800ppm.