The feasibility of friction stir welding to joining of AC4CH semisolid cast aluminum alloy with 6061 aluminum alloy plates was investigated, including the influence of the joining condition on the mechanical properties of the joints. Excessive heat input conditions with high tool rotational speed and low welding speed result in formation of large burrs. Although the hardness of the stir zone is scarcely affected by the welding condition, the welding speed as low as 1mm/s makes heat-affected zones on both sides softer than the stir zone. Better mechanical properties, such as the tensile strength of approximately 85% of the AC4CH base metal and the elongation exceeding the basemetal, are obtained under low heat input conditions.

In this study, with the aim of improving the fatigue characteristics of the A7075 aluminum alloy, A7075-T6511 alloy rod specimens were plated with electroless Ni-P with different compositions, and the fatigue characteristics were evaluated by a rotary bending fatigue test. The fatigue strength of the specimen plated with low-P type was higher than that of the un-plated specimen. However, the fatigue strength of the specimen plated with high-P type was significantly lower than that of the un-plated specimen, and the fatigue strength of the specimen plated with medium-P type was also lower though the extent was not so significant. It was speculated that these reductions in fatigue strength were due to hydrogen embrittlement by the hydrogen introduced into the specimen during the plating.

The interdiffusion in Ti-rich β solid solutions in Ti-Al-Zr alloys has been investigated at 1473 K. In the β Ti-Al-Zr alloys, the main interdiffusion coefficients, and , and cross interdiffusion coefficients, and , have positive values in the ternary alloys, and they have slight concentration dependence. The values of are larger than those of . In the Ti-Al-X（＝V, Cr, Fe, Co, Zr） alloys, the values of main coefficients are ＜ ＜ ＜ ＜ at 1473 K. The repulsive interactions exist between Al and X（＝V, Cr, Fe, Co, Zr）atoms in the Ti-Al-X alloys, because the ratio values of cross coefficients to main one are positive in sign. On the other hand, the interactions between Ti （solvent） and X （＝V, Cr, Fe, Co, Zr）（or Al） atoms are attractive in the present alloys, since the ratio of converted interdiffusion coefficients in the ternary alloys show negative values.

In this study, precipitation behavior in hot workings on Al-1%Mn alloy was investigated. It has been identified specimens used in this study show thermally stabilized substructures after plain strain compression (PSC) test as a hot working. PSC tests were carried out between 300°C and 500°C. By using small angle x-ray scattering (SAXS) method, dispersion state of precipitations formed in hot workings were estimated. It was considered minute precipitations less than 10 nm in diameter were formed in hot worked areas. These minute precipitations were increased with increasing in compression temperature. In invariant area heated at 400°C, precipitations less than 10 nm were not identified. By using of HAADF-STEM, these minute precipitations less than 10 nm were confirmed, and it was cleared due to EDS analysis the precipitations consist of four elements such as aluminum, manganese, iron and silicon.

Since 6000 series aluminum alloys have high hardness based on precipitation strengthening and good corrosion resistance, they are utilized as automobile body sheet panels in the industry. In order to reduce the weight of automobiles, further improvement of hardness is required. To improve the hardness, the process of severe plastic deformation before artificial aging (T8 treatment) was suggested. However, the effect of severe plastic deformation on the precipitation behavior of the alloys is not clear. In this study, 90% cold rolling was conducted for an Al-0.6Mg-1.0Si-0.5Cu alloy as the thermo-mechanical treatment. It was compared that precipitation behavior between T6 and T8 treated alloys by Micro Vickers hardness test, electrical conductivity measurement, differential scanning calorimetry and transmission electron microscopy. As the results, in T8 treated alloys, both precipitation strengthening and recovery softening happened during aging. However, the peak hardness of T8 treatment was larger than that of T6 treatment. The precipitation process was accelerated by lattice defects such as vacancies and dislocations introduced during 90% cold rolling. The precipitations in T8 treatment aged for 10.8 ks were identified as β”, β' and Q'. It was confirmed that β'(Q') phases precipitated directly along dislocations in 90% cold-rolled alloys.