The plate bending fatigue tests with stress ratio of -1 and 0 were conducted for the Mg-9mass%Al-1mass%Zn-2mass%Ca extruded plates, MIG joints and TIG joints. Fatigue limit of the plates along the extruded direction (ED) was smaller than that of the plates along the transverse direction (TD) for each stress ratio. It is likely that the anisotropy was attributed to the spread of basal pole in the ED and the rotation of basal pole toward the TD. Fracture occurred at the center of the specimens of MIG and TIG joints, and fatigue limits of both joints were lower than that of the extruded plates. Fatigue limit of TIG joints, however, was about 50 to 60% of MIG joints. SEM observations indicated that fatigue cracks initiated at the second phase particles (Al-Ca compounds) and propagated near them. Fracture occurred as a result of the crack connection. The size of the second phase particles in TIG joints was larger than that in MIG joints, so that the crack length was larger in TIG joints. It is likely that the larger size of the second phase particles was attributed to the lower fatigue limit of TIG joints.

In this study, two-layered porous aluminum consisting of A1050 commercial-purity aluminum and ADC12 Al-Si-Cu aluminum alloy was fabricated by joining A1050 and ADC12 porous aluminum with foaming process. As a joining method, press forming immediately after foaming of the two types of porous aluminum that were foamed at the same time was introduced. In addition, to promote material flow during joining, the pressing die was reciprocated in the horizontal direction during press forming. Preliminary experiments showed that the A1050 and ADC12 precursors can be foamed at the same time by applying black toner to the surface of the A1050 precursor. From the joining experiments, although the pressed surface and A1050 part of the porous aluminum was densified at an amplitude of 40 mm, it was found that a two-layered porous aluminum with good pore structures can be obtained at an amplitude of 5 mm. By the four-point bending test of the obtained two-layered porous aluminum, we observed pores of the porous aluminum on the fracture surface. This finding indicates that strong bonding can be obtained by press forming immediately after foaming with a reciprocation of the pressing die.

Thermal conductivity is useful to improve performance and manufacturing process for various products. In this study, thermal conductivity was measured for solution-treated Al-Si alloys, and the influence of solute Si on thermal conductivity was studied. For quantification of metallurgical structure, electrical resistivity was measured. Ingots of Al-Si alloys were prepared with Si content between 0.5 and 10mass%. Thermal conductivity was measured at room temperature (294～300K), λ, after heat treatment at 843K showed a good proportional relation to Si content up to 1.4%. The specimens of Si content above 5% showed negative deviations from the proportional relation, suggesting incomplete dissolution of silicon. Contribution per unit concentration of solute Si to the λ^‒1 was 0.856×10^‒3 W^‒1 m · K · mass%^‒1. Electrical resistivity was measured at room temperature (298K) and 77K. Electrical resistivity also showed a good proportional relation to Si content up to 1.4%. Contributions per unit concentration of solute Si to the resistivity at 77K and at 298K were 5.65 nΩm·mass%^‒1 and 5.71 nΩm·mass%^‒1, respectively. For specimens of Si content above 5%, volume fractions of Si particles were calculated from the measured values of thermal conductivity and electrical resistivity, respectively. Both of volume fractions were larger than calculated value from the concentration of solute Si.

One of the problems preventing the practical use of porous aluminum is the lack of strength and the difficulty of compositing it with other materials. In this study, we attempted to bond porous aluminum with a polycarbonate plate of high strength capability, insulation, and corrosion resistance to fabricate a composite material with improved strength and light weight, while maintaining its shock-absorbing properties. The precursor was heated by optical heating to fabricate porous aluminum and then the porous aluminum was cut by passing a cutter through it before it solidified. After cutting, the porous aluminum was moved to directly under the polycarbonate plate, and the latter was pressed onto the porous aluminum for bonding at 400°C. From the observation of the cross section of the bonded sample, it was confirmed that the polycarbonate plate had entered into the pores of the porous aluminum, creating an anchor effect that resulted in strong bonding between the porous aluminum and the polycarbonate plate. The cutting and bonding did not affect the pore structures of the porous aluminum, suggesting that the polycarbonate plate can be bonded to the porous aluminum immediately after cutting.