To realize the effects of alloy composition and processing conditions on the mechanical properties of the age-hardening aluminum alloys strengthened by cold-working processes, high-pressure torsion (HPT), high-pressure sliding (HPS) and cold-rolling were applied to the solution-treated aluminum alloys with various alloy compositions. Tensile testing was carried out using a tensile test piece with the same gauge part morphology regardless of cold-working methods. In any alloy system, the specimens subjected to the cold-working process showed higher strength than the aged specimens. In 2000 series alloys, the increase of copper and magnesium contents did not result in higher strength, but in lower ductility. In 6000 series alloys, both strength and ductility were improved with increasing of copper content. In 7000 series alloys, increasing the zinc content increased the strength, but significantly reduced the ductility in some cold-working processes. In any cold-working process, ultimate tensile strength showed a good correlation with nominal solute content. The higher solute content resulted in higher strength but in lower ductility.

Solution treated Al-Cu-Mg alloys with three different compositions were subjected to high-pressure torsion (HPT) for 1 to 50 turns, and then aged at 423 K. By conducting HPT process, the hardness of the three alloys significantly increased after 50 turns, and the average grain sizes were refined to 130-140 nm. After aging treatment, the hardness was further increased to 271 HV, 288 HV and 273 HV in the peak aging condition for the Al-4Cu-1.5Mg, Al-4Cu- 3Mg and Al-5Cu-3Mg (in mass%) alloys, respectively. The contribution of several strengthening mechanisms was quantitatively evaluated in terms of grain boundary hardening, dislocation hardening, solid solution hardening and cluster/precipitation hardening. It is shown from the quantitative evaluation that simultaneous strengthening due to grain refinement and nanoscale precipitates is successfully achieved by combined application of HPT process and subsequent aging treatment.

Tensile properties have been evaluated for four kinds of Al-Mg-Si base alloys which were cold rolled by 90% and subsequently aged for 1 min, 30 min, 18 h at 170°C. To study the effect of alloy compositions and aging conditions on deformation behavior, fracture surface observations and strain distribution analysis during tensile deformation were performed. Strain distribution in the tensile specimens was evaluated by digital image correlation method. The ductility in the specimens aged for 1 min and 30 min after cold rolling was improved due to increase in both uniform and local elongation. All the specimens showed ductile fracture, while the specimen added with 0.71%Fe showed slightly lower ductility. The addition of copper improved strength without deteriorating ductility. The relation between mechanical properties and microstructure is discussed to obtain basic information required to improve strength and ductility of Al-Mg-Si alloys.

Hypervelocity projectile perforation behavior of 6000 series aluminum alloys in the subcommittee of The Japan Institute of Light Metals was examined and compared commercial 6061 aluminum alloy. A two-stage light-gas gun was used for impact experiments at high velocities. Yield stress clearly affected perforation hole area. Ejecta length and the cumulative number of ejecta was almost the same among four specimens. Ejecta cone shape was also the same.

Aging behavior, cluster formation including near grain boundaries, and mechanical properties of Al-11mass%Zn- 3mass%Mg-1.4mass%Cu (-0.2mass%Ag) alloy were investigated. The effect of Ag as a microalloying element was also clarified. The Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy showed higher aging hardening ability and shorter time to peak aging than the Al-5%Zn-2%Mg (-0.3%Ag) alloy from the early aging stage. The effect was greater with the addition of Ag, showing that the effects of solute content and micro-alloying elements on age hardening were recognized. 3DAP analysis revealed that Ag contributed significantly to the initial stage of cluster formation even when the solute elements were high. It was also found that clustering occurred in the vicinity of the grain boundary at a high density and fineness from the early stage of aging. By increasing the solute content of Zn and Mg to 11 mass% and 3 mass%, respectively, the tensile strength of the alloy was over 800 MPa, and the addition of Ag further increased the strength.

The weldability of an Al-11%Zn-3%Mg-1.4%Cu alloy by friction welding was investigated and the effects of T6 treatment during and after welding on the microstructure and joint properties were clarified. Fine grains were formed at the interface of the as-welded joint and were coarsened by the T6 treatment. η' phase was coarsened at the interface due to friction welding, on the other hand, fine η' was precipitated again by T6 treatment after welding. The joint efficiency in tensile tests was 72% for the as-welded joint, but recovered to 89% by T6 treatment after friction welding, and all fracture locations were near the interface layer. Tensile strength differed depending on whether the grain elongation direction was parallel or perpendicular to the tensile direction, suggesting that the grain shape near the interface was the cause of joint failure.

A phenomenon that Al-6.0%Zn-0.75%Mg alloy sheets furnace-cooled after solution heat treatment had higher strength than water-quenched sheets under specific aging condition was reported. However, the strengthening mechanism related to furnace-cooling had been not clarified yet. In this research, replication test of the strengthening phenomenon of furnace-cooled sheets and the microstructural change during natural aging and artificial aging at 200°C after furnace-cooling after solution heat treatment was investigated by tensile tests, SAXS measurements, STEM observation and electrical conductivity measurement. The strengthen phenomenon of furnace-cooled sheets was reproduced. In as-furnace-cooled sheets, 2-5 nm clusters which induced lattice strain were observed in LAADF-STEM image apart from atomic number contrast in HAADF-STEM image. The clusters seemed to be generated during furnace cooling. The clusters seemed to cause suppression of reversion and promotion of age hardening in furnace-cooled material.

To elucidate the relationship between aged microstructure and fatigue crack initiation, tensile fatigue tests and analyses on crack initiation sites were performed on T4- and T6-tempered specimens of an Al-Cu-Mg alloy containing the same amount of Cu and Mg as 2024 alloy but with almost no Mn, Fe or Si. Despite lower statistic strength, T4 specimen had higher fatigue strength than T6 specimen. Crack initiation took place on the surface at slip bands inside the grain and at grain boundaries in T4 and T6 specimens, respectively. The aged microstructure in T4 specimen was presumed to consist of GPB (1) zones with almost no precipitate free zones (PFZs) along grain boundaries, while that in T6 specimen was composed of coarse S phase particles on grain boundaries, S’ phase laths and probably GPB (2) zones inside the grain with PFZs of about 600 nm width. Hence, it was deduced that the fatigue cracks occurred by the intrusion and extrusion mechanism in T4 and T6 specimens along persistent slip bands and along PFZs, respectively. The latter was caused by softer PFZs in T6 specimen than the matrix of T4 specimen, resulting in an earlier crack initiation and consequently lower fatigue strength.

Type-B serrations were observed during room-temperature tensile deformation of Al-2.17mass%Mg alloy with an average grain size of 12 μm. Digital image correlation was used to visualize Portevin-Le Chatelier (PLC) bands, and microstructural changes in these bands were observed by in-situ X-ray diffraction measurements using synchrotron radiation at SPring-8. The results indicated that the overall density of dislocations, including both mobile and pinned dislocations inside the PLC bands, increased substantially as the bands formed. This suggests that serration occurs due to an increase in the mobile dislocation density resulting from the formation of new dislocations from sources inside the PLC bands.

Attempts were made to synthesis Al-HEA alloys by adding high entropy alloys (HEA) to Al using the mechanical alloying (MA）-spark plasma sintering (SPS) process. CrMnFeCoNi HEA (Cantor alloy) was selected as the HEA to be added to Al, with an addition of 10 mass%. The case where Cantor alloy is added to Al (Al-10 (CrMnFeCoNi)) and the case where elemental powders of the constituent elements of Cantor alloy are added (Al-2Cr-2Mn-2Fe- 2Co-2Ni) are compared. Hardness and solid-state reaction were evaluated by hardness testing and X-ray diffraction. The highest hardness was exhibited 254 HV at MA16 h for Al-10 (CrMnFeCoNi) and 239 HV at MA8 h for Al- 2Cr-2Mn-2Fe-2Co-2Ni, which is higher than A7075-T6 (170 HV). Compounds between Al and the constituent elements of the Cantor alloy were identified in the SPS material for each test specimen, suggesting that the main reason for the higher hardness is the compounds formed by the solid-state reaction. No significant difference in the hardness of each specimen due to the different addition methods.

Recently, it has been found that Mg-Sc alloys with a body-centered cubic (bcc) structure have excellent workability, strength and ductility, and exhibit superelasticity at room temperature. However, due to the high cost of Sc, such alloys have not yet been put into practical use. Therefore, in this study, Zr, which is less expensive than Sc, was added to a Mg-Sc alloy, and a single-roll rapid solidification method was used to directly obtain ribbons from the molten metal. The thickness of the resulting alloy ribbons was measured using a digital microscope, the crystal phase was identified using X-ray diffraction (XRD) analysis, the microstructure was observed using field-emission scanning electron microscopy, and the hardness was evaluated by a Knoop hardness test. The results indicated that continuous Mg-Sc-Zr alloy ribbons with a uniform width and a thickness of about 50 μm could be obtained. From the XRD results, the rapid cooling process caused an increase in the fraction of the bcc phase relative to that in a Mg-Sc ingot; this phase is stable at higher temperatures. The Knoop hardness of the Mg-Sc-Zr alloy ribbons was found to increase with increasing Zr content, which is considered to be due to microstructural refinement.

With the recent digitization, electronic equipment housings are required to be thin-walled and have rigidity, heat dissipation, corrosion resistance, and electromagnetic shielding properties. Magnesium alloys are promising materials that satisfy these requirements. Mg-Al alloys have good castability and high strength, but their thermal conductivity decreases. In general, adding alloying elements to magnesium decreases thermal conductivity the effect of aluminum addition is significant. It was found that adding calcium to Mg-Al alloys to form Mg-Al-Ca (AX) alloys results in higher thermal conductivity than that of Mg-Al alloys. However, AX alloys have poor corrosion resistance and require post-treatment such as surface treatment. In this study, AX64, which has high thermal conductivity among the AX series alloys, was used as the basic composition, and corrosion resistance was improved by adding manganese and misch metal, and an attempt was made to improve corrosion resistance and emissivity through surface treatment. The change in thermal conductivity by heat treatment was also investigated. Experimental results showed that the addition of manganese and misch metal improved corrosion resistance and thermal conductivity. Plasma anodization also improved corrosion resistance and emissivity. Heat treatment of these alloys at 400°C improved the thermal conductivity with longer holding time.