Among Al-Zn-Mg alloys, A7003 alloy is considered to be an excellent alloy from the viewpoint of weldability because it is an alloy with relatively low Zn and low Mg composition. In this paper, changes in mechanical properties and microstructure during aging treatment are investigated by the addition of Si in the Al-5.6 mass%Zn-0.75 mass%Mg alloy containing Cu, Mn, Zr and Fe. Cast billets of alloys with different Si contents (Si: 0.05 mass%, 0.15 mass%, and 0.30 mass%) were prepared, and these cast billets were homogenized and extruded. After extrusion, four aging treatments were performed: one step aging at 423 K for 8 hours, and two step aging at 373 K for 3 hours, 6 hours, and 9 hours, followed by 423 K for 8 hours. The higher the amount of Si, the smaller the thickness of recrystallization layer near the inner surface and near the outer surface, and the smaller the existence rate of recrystallized grains in the cross section. After one step aging at 423 K for 8 hours, Si: 0.05 mass% showed lower strength than Si: 0.15 mass% and Si: 0.30 mass%. On the other hand, two-step aging resulted in Si: 0.05 mass%, Si: 0.15 mass%, and Si: 0.30 mass% with similar strength. The low strength of Si: 0.05 mass% after one step aging at 423 K for 8 hours is thought to be due to the coarse η phase, which was precipitated in the grain boundaries and grains. In Si: 0.15 mass% and Si: 0.30 mass%, Al (Mn, Fe) Si which formed during homogenizaiton process is present in the grain boundaries and grains after extrusion. It is thought to suppress the generation of the precipitate of the coarse η phase in the aging at 423 K for 8 hours, which is a condition that the coarse η phase is easy to generate.

Solidification and precipitation behavior for Al-Si alloys were investigated by differential scanning calorimetry (DSC). Solidus values measured by DSC method agreed with calculated solidus values from equilibrium phase diagram. Liquidus values measured by DSC was deviated from calculated values by phase diagram. Comparison of solid fraction calculated from specific heat curves and calculated values from phase diagram were showed partially deviation. Since Al-Si alloys used in this study were contained about 0.1% Fe, solidification behavior was considered to be slightly different from Al-Si binary phase diagram. From the measured heat flux curves for solution treated Al-Si- alloys, exothermic reaction due to precipitation of solute Si and endothermic reaction due to dissolution of Si precipitates were detected. With heating of specimens, solute Si were considered to be precipitated from the supersaturated solid solution first, and then precipitated Si during cooling after solution treatment and during measurement were dissolved. For Al-1.4mass%Si alloy, the amount of precipitated Si during measurement analyzed from DSC curves was estimated to be about 84% of solute Si, corresponding to 1.26vol.% in volume fraction. In this study, it was indicated that solidification and precipitation behavior can be quantitatively analyzed by DSC measurement for systems with known phase diagram.

High thermal conductivity ternary Mg alloys composed of Zn and Y pair with a negatively high mixing enthalpy was developed by optimization of alloy composition and heat-treatment conditions. Optimal alloy composition was Mg-1.88Zn-0.75Y (at%) alloy, in which the ratio of Zn content to Y content was 2.5 and the Y content was 0.75 at%. The alloy was composed of α-Mg＋W phase (Mg₃Zn₃Y₂）＋I phase (icosahedral Mg₃Zn₆Y). Heat treatment under the optimal heat treatment conditions, where temperature, time and cooling rate were 633 K, 15 h and air cooling, respectively, improved the thermal conductivity from 114 to 141 Wm^‒1K^‒1 that corresponds to 90% of the pure Mg thermal conductivity. Fine W phase precipitation in α-Mg matrix by the heat-treatment caused a reduction of solute Y element in α-Mg matrix, resulting in improvement of the thermal conductivity.

Yamamoto’s rate equation was applied to two-step age hardening of an Al-6%Zn-0.75%Mg alloy. All aging processes at 160–200°C were described as the sum of three precipitation reactions, that is, spherical, plate-like, and rod-like precipitation independent of the holding time at room temperature (RT). These results agreed with the observation of TEM microstructures. Based on the activation energy of diffusion calculated from the rate equation, it was suggested that the diffusion of zinc controlled the spherical precipitation reaction, and the diffusion of magnesium did the rod-like one. The plate-like precipitation reaction which depended on the holding time at RT is controlled by the diffusion of zinc for a short time and the one of magnesium for a long time. These precipitation reactions were related to the meta-stable and stable phase particles. The comparison between electrical resistivity (ER) and Vickers hardness (HV) changes at 160°C aging showed that the HV change was faster than ER one in the long holding time at RT. On the other hand, the ER change became faster than HV change in the short one at RT. This difference is related to the formation of clusters and GP zones that are formed by holding at room temperature.

The precursor method is one of the methods used to fabricate porous aluminum. In this method, porous aluminum can be fabricated by heating the precursor for foaming by generated gas from the internal foaming agent. In our previous study, shaping of porous aluminum can be conducted by forming immediately after foaming without collapsing the internal pores. In this study, we attempted to fabricate a large sample by joining two small pieces of porous aluminum immediately after foaming and shaping them at the same time. As a result, it was found that the two samples could be joined without collapsing the pores in the porous aluminum, and a mountain-like shape could be given to the samples. From the four-point bending test, pores were observed at the fracture surfaces, indicating that most of the samples fractured at the base porous aluminum. Therefore, it was shown that strong joining between two porous aluminum can be achieved.