In this study, nanostructure formation and age-hardening behavior of an Al-6Zn-0.79Mg alloy were investigated by varying quenching conditions during solution heat treatment. For the sample furnace-cooled from 723 K to around 303 K, the hardness after cooling was higher than the hardness after quenching of the WQ sample, and the maximum hardness was equivalent to that of the WQ sample. On the other hand, samples taken out of the furnace at around 373 K during furnace cooling showed a slower hardening rate and a relatively lower maximum hardness. Microstructure observations at as quenched (A.Q.) and as cooled (A.C.) state showed nanostructures in the FC-303K sample that were considered to have formed during furnace cooling, which is consistent with the structure reported as GP (I) with TCO structure. Clusters and GP zones formed during furnace cooling tend to form at temperatures below 373 K, suggesting that they contribute to age hardening.

Hardness of furnace-cooled Al-6Zn-0.79Mg (mass%) alloy is larger than that of the water-quenched alloy. Just after the furnace cooling, strains remain as a high density of dislocations, leading to nanoscale local lattice distortions of the fcc matrix. This phenomenon happens in conjunction with compositional fluctuations composed of Zn-vacancy and Zn-Mg rich regions. Consequently, introduced dislocations bring about strengthening due to cooling strain hardening. The early stage of the decomposition leads to nucleation sites for the latter strengthening phases.

The formation of solute clusters in Al-Zn-Mg alloys was investigated using first-principles-based Monte Carlo simulations. After the formation of the truncated cube octahedron (TCO) shell composed of eight Mg atoms and thirty Zn atoms, the Zn atom at the face-center site moved to the octahedral site, resulting in an interstitial Zn and vacancy pair in the TCO shell. If a vacancy was introduced in the Monte Carlo simulation, at the nearest neighbor of the vacancy, the number of Zn atoms increased first, followed by the number of Mg atoms. The most stable vacancy-solute cluster is V- Mg₄Zn₈. This result suggests that thermal equilibrium vacancies were quenched and embedded in the vacancy-solute clusters in water-cooled specimens in Al-Zn-Mg alloys.

Hydrogen embrittlement in Al-Zn-Mg-Cu alloys is suggested to originate from debonding of the η phase interface. Previous studies have shown that intragranular T phase precipitation, facilitated by increased Mg content, contributes to the mitigation of quasi-cleavage fracture. However, the role of T phase precipitation on the grain boundary in suppressing intergranular fracture remains unclear. In this study, in-situ observational techniques were used to examine the relationship between grain boundary precipitates and hydrogen-induce intergranular cracking. Obtained results showed that while the T phase precipitates in the matrix of Mg-enhanced alloy, the η phase predominates on grain boundaries, which lead intergranular fracture. The presence of numerous voids at intergranular crack tips suggests that void nucleation along grain boundaries and subsequent coalescence is the primary mechanism of crack propagation. The observed void formation at η phase interfaces is consistent with first-principles calculations and supports the concept that intergranular fracture originates from debonding at η phase interfaces.

In this study, the joint properties of dissimilar materials joined by friction welding between an Al-11%Zn-3%Mg-1.4%Cu alloy and SUS304 stainless steel was evaluated. Additionally, to compare the weldability, friction welding was also conducted on dissimilar materials involving the A7204 alloy, A7075 alloy, and SUS304 stainless steel. The A7204/SUS304 joints and the A7075/SUS304 joints both fractured in the aluminum alloy at tensile strengths of 316 MPa (joint efficiency of approximately 75%) and 353 MPa (joint efficiency of approximately 100%), respectively. It was found that by reducing both the friction pressure and the rotational speed, the interface could be maintained at a relatively low temperature for an extended period, thereby suppressing excessive growth of the intermetallic compound (IMC) layer while still achieving the joint. In Al-11%Zn-3%Mg-1.4%Cu alloy, the tensile strength increased to 377 MPa compared to the standard alloy, but the fracture occurred at the interface. FEM analysis revealed that the stress at the interface during tensile deformation increased more significantly at the edges than at the center, leading to stress localization. It was suggested that in such cases where localized stress occurs, interface fracture is more likely to occur.

Magnesium molybdate (MgMoO₄) were prepared by corrosion reaction of metallic molybdenum and magnesium in hydrogen peroxide. The hydrogen peroxide was acidified due to the corrosion of molybdenum, and then magnesium dissolved quickly when added to the solution. It was found that MgMoO₄ powders were prepared by calcinating at more than 973 K. The MgMoO₄ powder which obtained after the calcination at 973 K had the diameters from 0.4 μm to 9.3 μm. For comparison, magnesium molybdate was prepared by a solid-state reaction method using molybdenum oxide and magnesium oxide as raw materials. It was identified that the powder which was calcinated at 1073 K was MgMoO₄ and the particle size was 2.1 μm to 26.1 μm.

In developing ribbons for use as anode materials in innovative rechargeable batteries, magnesium ribbons were manufactured using a single-roll rapid solidification method. The quality of ribbons, such as their surface characteristics and defects, was considered to be largely determined by the manufacturing conditions of single-roll rapid solidification method, and it was also reported that shape of nozzle used to spray molten magnesium also had a significant effect on the quality of ribbons. In this study, ribbons were produced using nozzles with various internal gradient angles, and the surface properties, cross-sectional structure, and internal and external defects of the ribbons were evaluated. In actual ribbon production, it was confirmed that a nozzle with a smaller gradient angle could produce ribbons with a stable yield of over 70%. This is because adding a gradient shape allows smooth molten metal to be sprayed out. In the microstructure observation of the ribbons, a network-like second phase was observed near the free-solidification surface. A difference in cell size was also confirmed with the change in nozzle shape. In addition, the relationship between cell size and hardness was investigated, and it was confirmed that the hardness value decreases as the cell size increases.

Aluminum foam is a material that contains many pores and has excellent impact energy absorption and thermal insulation properties. The foaming process affects the mechanical properties of the aluminum foam due to variations in the pore structures. In this study, we attempted to estimate the plateau stress of Al-Mg-Si aluminum alloy A6061 aluminum foam from its X-ray CT images using machine learning. Using a machine learning model that has already been trained on industrial pure aluminum A1050 aluminum foam, a model was created to estimate the plateau stress of A6061 aluminum foam by transition learning. It was found that the use of transfer learning reduced the training time by 26% while achieving the same estimation accuracy as the model created by learning from the beginning without using transfer learning.