In this study, grain refinement performance of aluminum cast by grain refiners containing spherical-shaped Al₃Ti particles is studied. Spherical Al₃Ti particles with D0₂₂ structure were prepared by gas atomization method. The sieved particles in the range of 75–150 µm and 150–212 µm were sintered with pure aluminum particles by spark plasma sintering (SPS) to obtain Al–10 vol% Al₃Ti grain refiner with spherical Al₃Ti particles. It is found that the spherical Al₃Ti particles can become favorable heterogeneous nucleation sites for solidification of aluminum. However, grain refining performance has a strong fading trend. When the refiner was heat-treated at elevated temperature, the spherical Al₃Ti particles were divided into smaller parts. This is because the spherical Al₃Ti particles prepared by gas atomization method are polycrystal.

To predict hot tearing in direct chill (DC) casting and shape casting of aluminum alloys using thermal stress analysis, cooling rate dependence of viscoplastic properties in a partially solidified state is indispensable. Based on viscoplastic properties determined from experiments, this study develops a method to predict the temperature dependence of viscoplastic properties at an arbitrary cooling rate through the Clyne–Kurz microsegregation model. For validation of the developed method, tensile tests were performed on Al–5 mass%Mg alloy in a partially solidified state at three cooling rates. Results show good agreement between the predicted values and experimentally obtained values, which demonstrates that the developed method is effective for predicting the cooling rate dependence of viscoplastic properties.

In this study, a simple B addition process for producing 6063 aluminum alloy containing 0.03% B was investigated. KBF₄ (98.0 mass%) and commercial-purity aluminum powder (>99.7 mass%, particle size: 30 µm) were weighed, mixed, wrapped in aluminum foil, and placed in a phosphorizer. The phosphorizer was then immersed in a molten 6063 aluminum alloy at a temperature of 720, 760, 810, or 860°C. The boron recovery rate depends on the amount of aluminum powder in the mixture and the melt temperature. Optimizing these factors gives a 90% boron recovery rate. Excess aluminum powder in the mixture leads to an increase in the specific surface area of the KBF₄ particles and promotes the reaction, 2KBF₄+3Al→AlB₂+2KAlF₄. The AlB₂ contained within the KAlF₄ migrates into the melt as the KAlF₄ evaporates. Therefore, a mixed powder of KBF₄ and Al can be an effective means of adding boron to 6063 aluminum alloy if the amount of aluminum and the temperature are carefully controlled. For the present experimental conditions, it was difficult to find AlB₂ in the alloy by EPMA, because only a small amount of B was added. B seems to form a solid solution with aluminum without forming coarse intermetallic compounds.

This study investigated the low-temperature creep mechanisms in ultra-fine grained aluminum made by accumulative roll bonding. The low-temperature creep behaviors in ultra-fine grained aluminum with grain size of 0.39 µm were divided into four regions by three certain stress values, σ_my, σ_multi and σ_y. σ_my is stress for dislocation movement, σ_multi is stress for dislocation multiplication, and σ_y is yield stress. First, below σ_my, plastic deformation was negligible. Second, from σ_my to σ_multi, creep deformation with n=2.5 occurred by grain boundary sliding. Third, from σ_multi to σ_y, creep deformation with n=7.2 occurred by intragranular recovery of dislocations. Last, above σ_y, power-law breakdown was confirmed.

This study investigated the effect of post-brazing cooling rate and Si addition on the intergranular corrosion (IGC) susceptibility of brazed Al–Mn–Cu alloys by electrochemical analysis and microstructure observation. Water-quenched samples after brazing exhibited no IGC susceptibility, whereas slowly-cooled samples were prone to IGC. The results suggest that IGC is caused by precipitation during cooling. In addition, it was observed that IGC susceptibility depended on the Si content. An alloy sample with a low Si-additive content exhibited high IGC susceptibility because Mn/Cu-depleted zone was formed near the grain boundaries as a result of the preferential precipitation of Al₆(Mn, Fe) and CuAl₂ on the grain boundaries. In contrast, moderate Si addition inhibited IGC because the decrease of the Mn content in the grain interiors due to enhanced precipitation of Al₁₅(Mn, Fe)₃Si₂ in the grain. Additionally, Cu-depleted zone also disappeared because preferential precipitation of CuAl₂ on the grain boundaries was prevented. The excess-Si alloy exhibited high IGC susceptibility because Si-depleted zone formed around the grain boundaries as a result of the preferential precipitation of coarse Si particles on the grain boundaries although the Mn/Cu-depleted zones were not formed.