The 6061 extruded sections such as the hollow shape have a few weld parts, and the microstructure is recrystallized around the weld part. The quality and microstructural control of the weld part is very important for the machine parts as the mechanical properties depend on the difference of deformation behavior between weld part and non-weld one. The purpose of our study is to investigate the deformation mechanism of 6061 extruded alloys having the weld part. In this paper, the tensile property of 6061 extruded alloys having the weld part was evaluated as compared with the non-weld one. As a result, the elongation of 6061 extruded alloys having the weld part was lower than that of the non-weld one. The result analyzed with the Electron Backscatter Diffraction Patterns (EBSPs) showed that the weld part was the recrystallized structure, and the non-weld part was the un-recrystallized one having subgrains. Then the texture structures were different between the weld part and the non-weld one. The tensile deformation of 6061 extruded alloys having the weld part depended on the difference of texture structure (at same the time the Taylor's factor, M, depends on texture structure) such as the formation of discontinuous structures. Therefore the elongation values obtained from tensile test does not show the real ductility behavior, and the considerations of deformation mechanism that depend on microstructures in parallel parts determine the real ductility of aluminum alloys having the weld part.

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The objective of this research is to obtain basic fatigue characteristics of extruded AZ61 magnesium alloy in ambient air (20~50°C and 55~80%RH) . Fatigue tests were performed under tension-compression loading with stress ratio R = −1, frequencies of 1 and 10 Hz. At 55%RH, S–N curve clearly showed the fatigue limit, which was 145–150 MPa for both 20°C and 50°C. At a higher humidity of 80%RH, fatigue fracture occurred along the extrapolated S–N line even in the lower stress regime than the fatigue limit, which is known as corrosion fatigue. Time-dependent fatigue behavior was observed in the stress region lower than the fatigue limit, while cyclic-dependent fatigue behavior was observed in the stress region higher than the fatigue limit. In the corrosion fatigue regime, corrosion pits were observed on the specimen surfaces and also at the fatigue initiation point on the fracture surfaces. The corrosion pits were initiated at very early stage of fatigue and grew to make a fatigue crack started at about half of the fatigue life. Slip deformation on the specimen surface as well as humidity will be the essential factor to form corrosion pits.

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In hot-rolled sheets bands of high purity Al used for the fabrication of electrolytic capacitors, textures and microstructures were investigated in detail. It was found that both textures and microstructures were quite inhomogeneous in the thickness direction. Regions just below the surface were completely recrystallized into fine, equiaxed grains, giving {111} <110> textures. These were followed by regions giving {113} <110> textures, which contained a small amount of unrecrystallized grains. Below these, the materials were partially recrystallized up to the 1/2 thickness. With increasing depth, the fraction recrystallized decreased rapidly. Since transition from shear deformation to biaxial deformation occurred in these regions, textures observed in these regions were complex. In the 1/2 thickness, normal β fiber textures were not observed. Although {110} <113> and near {123} <634> orientations were strong, {112} <111> was very weak. Instead, {100} <001> was rather strong. This is because partial recrystallization readily occurred in this high purity material even in the 1/2 thickness.

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In hyper-eutectic Al–Si alloys fabricated by 4–N aluminum and 5–N silicon, the morphology of primary silicon crystals at constant temperature of the solid-liquid co-existent temperature region was investigated. Supersaturated, non crystallization of silicon, alloy made by rapid solidification process were re-melted at the solid-liquid co-existent temperature region. The primary silicon was crystallized to the blocky shape. In the case of quenching by the solid-liquid temperature region after the melting, the primary silicon crystals grew to the petal shape. These crystallizations grew with same shape during isothermal holding at the solid-liquid co-existent temperature region. The primary silicon grew that the ration of length/width was reduced slightly, in the case of continuous cooling.

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Al–1%Mg₂Si–0, −0.17, −0.43, −0.72%Cu alloys were solution treated for 3.6 ks at 848 K, water quenched and aged at 473 K. Behavior of added Cu during these heat treatments and effect of the Cu on age-hardening were investigated by resistometry and tensile test with assist of transmission electron microscopy. The resistivity in as water quenched state well coincides with the value calculated from 0.023 mass%Fe, the equilibrium solubility at 848 K in Al–Fe binary system, and all of other elements in solution. Moreover, the resistivity increases linearly with amount of the added Cu. Namely all of the added Cu is dissolved in the as quenched state. By Cu addition, the initial age-hardening rate at 473 K aging is increased and the softening with over-aging is suppressed. Though the Cu addition increases proof stress at peak age-hardening, it also decreases the resistivity decrement from the as quenched state caused by the aging. This discrepancy, that the small total amount of precipitates, which is suggested from small decrement of resistivity by the peak aging, gives the larger age-hardening, can be explained by the decrease in average length with Cu addition which may be directly related to the increase in number of needle shaped precipitates per unit area.

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For the purpose of grain refinement, the development of the microstructure of 6061 aluminum alloys during asymmetric warm-rolling was studied by electron backscatter pattern (EBSP) analysis, as well as optical and transmission electron microscopy, and compared with that developed during conventional warm-rolling. In asymmetrically rolled sheets to a thickness reduction of 91.8% at 300°C, new fine grains with an average size of about 1 μm are evolved almost uniformly throughout the thickness. The fraction of fine grains in asymmetrically warm-rolling sheet increased with an increase in thickness reduction and a rise in temperature, whereas for conventionally warm-rolled sheet, the usual fibrous microstructure is predominant. The evolution of new fine grains during asymmetric warm-rolling seems to be due to the subgrain formation and the development of the subgrain into fine grain promoted by a simultaneous action of two deformation modes, namely compression and additional shear deformation. However, the obvious growth of fine grains was observed during solution treatment. For suppression of such a grain growth, scandium addition to 6061 alloy is effective.

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