The present study investigated the effect of trace titanium (Ti) addition on high-temperature creep properties of a heat-resistant quinary aluminum (Al) alloy, with a composition of Al-5Mg-3.5Zn-2Cu-2Ni (mol%). Both the quinary alloy and Ti-added alloy were solution-treated at 480°C and then aged at 200°C for 10 hours. The creep tests were conducted at 200°C under 105 MPa. The addition of trace Ti element reduced the minimum creep rate and delayed the onset of the tertiary creep stage (creep acceleration), resulting in the extended creep rupture life of the Al-5Mg-3.5Zn-2Cu-2Ni quinary alloy. The creep rupture life of the Ti-added alloy was higher than that of the A7075 alloy but lower than that of the A2618 alloy, whereas the initial creep rate (up to 0.2% in strain) of the Ti-added quinary alloy was lower than that of the A2618 alloy. The superior creep properties were presumably due to the enhanced stability of the fine precipitation morphologies of the T-Al₆Mg₁₁Zn₁₁ phase by solute Ti inside the α-Al matrix.

The present study investigated the influence of additional Mg on the intergranular corrosion (IGC) susceptibility of brazed Al-Mn-Si-Cu alloys. IGC did not occur in the water quenched samples, whereas samples treated with slow cooling rate showed high IGC susceptibility. As a result of anodic polarization measurement, non IGC susceptibility samples showed a single pitting potential, but high IGC susceptibility samples showed double pitting potentials. On slowly cooled Al-Mn-Si-Cu-Mg alloys, the precipitation of Al₁₅ (Mn, Fe)₃Si₂ were observed in the grain interiors and on the boundaries, but Q-phase on the grain boundaries. Precipitated Q-phase induced forming Si/Cu/Mg-depleted zone near the grain boundaries. This zone, of which pitting potential is less noble than the grain, dissolved preferentially, hence IGC susceptibility increased. Furthermore, we clarified additional Ti improved the IGC susceptibility of Al-Mn-Si-Cu-Mg alloys. It was considered that potential gap due to Ti layered distribution prevented intergranular corrosion progress.

In this study, we examined a method for whitening of aluminum surface by anodizing in sulfuric acid solution, with the aim of industrializing the process. Anodic oxidation in sulfuric acid solution at 2.5 Adm^‒2 for 120 s achieved whitening of the aluminum surface, but localized burning occurred. When anodizing was performed at low current density after anodizing at higher current density for short time (2.5 Adm^‒2 for 4.5 s), white anodic film was successfully obtained without burning. Cross-sectional SEM (scanning electron microscopy) observation of white film revealed that the etching by pretreatment created an uneven surface, and the pore branching created an uneven metal- oxide interface. The fluctuating value of the film thickness obtained by length measurement using SEM were 0.2-0.3μm. This value is sufficient to whiten the anodic film due to increase of diffusion reflection at the film surface and the metal-oxide interface. These results indicate that the difference in peak voltage between the first and second anodizing resulted in the formation of a branched pore structure and the achievement of film whitening.

To reduce CO₂ emission, recycling Al scrap into wrought alloy is desired. However, impurity elements are inevitably contained in the Al scrap recovered from the society, and most of them are difficult to be removed by the current pyro-metallurgical processes. Mn is one of the major alloying elements of Al alloys and steels, and is contained in Al scraps. Therefore, a removal method of Mn from Al is necessary. Mn easily forms an inter-metallic compound with Al; on the other hand, it is immiscible with Mg in the liquid state, which suggests that the repulsive interaction between Mg and Mn in molten Al enhances the precipitation of intermetallic compounds such as Al₆Mn. This study proposed Mn removal from molten Al-Mg alloy through precipitation of Al₆Mn inter-metallic compound. Molten Al-Mg alloy was equilibrated with Al₆Mn, and the reducing limit of Mn concentration was thermodynamically discussed. Mn concentration becomes lower at higher Mg content of molten Al and lower temperature. The activity coefficient of Mn in molten Al-Mg alloy was increased with the addition of Mg, and the following equation was obtained as a function of temperature and molar fraction of Mg:

It was found that Al₆Mn will precipitate due to the repulsive interaction of Mn and Mg when the Mg content of Al is increased. The thermodynamic analysis showed the possibility of reducing the Mn content of Al to 0.0030 mass% at 733K and 34 mass%Mg by the present removal process.