Al–Mg–Si series alloys have some sensitivity of liquation cracking in welding heat affected zone (HAZ). In this report, influence of manganese in 6082 on susceptibility of this liquation cracking was studied using a welding thermal stress cycle simulator. As the results of the butt welded joints, this liquation cracking was suppressed by the addition of Mn. From the welding thermal stress cycle simulator, it has been cleared that with the addition of Mn, the lower limit of the brittle temperature range between nil-ductility temperatures on heating process and on cooling process, was raised to the same or higher temperature than solidification temperature of the weld metal. This was because that the effective Si content in matrix was reduced by generating the Al–Fe–Mn–Si compounds due to the addition of Mn. In this case, solidification shrinkage strain of weld metal did not work to open the solid state grain boundary in HAZ to cracking easily.

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The effects of 20°C natural aging and 20% cold work on the strength of 2013 aluminum alloy (Al–1.7Cu–1.0Mg–0.8Si–0.15Cr: mass%) aged at 170°C for 8 h have been investigated. The strength of T6 samples slightly decreased with increasing the time of natural aging after solution heat treatment. Though the amount of precipitation hardening was lower than T6 specimens, the strength was improved by combination of natural aging and cold working, namely T8 temper. However, cold working just after solution heat treatment resulted in lower precipitation hardening, and thus the T8 strength was lower than that of the specimens with prolonged natural aging after solution heat treatment. It is suggested that the lower precipitation hardening resulted from the heterogeneous distribution of the hardening precipitates formed on the microbands.

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Laser joining for different materials between 1050 aluminum sheet of 1 mm thickness and polypropylene sheet of 2 mm thickness using a newly developed insert sheet was studied. The diode laser-irradiation to the polypropylene side was carried out in air. The effects of the aluminum surface state on the joining properties were examined. The joining strength increased with the increase in aluminum surface area except for the surface with the intense ruggedness. It was found that the chemical condition of aluminum surface treated with the acid or alkaline solution strongly affected the joining strength rather than the surface roughness.

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Aluminum alloy sheets are being increasingly used to reduce the weight of an automotive body. Al–Mg–Si alloys have been used because they have favorable properties for automotive bodies. One of the important requirements of these alloys is the ability to resist fracture while bending. In this study, the influence of crystal orientations on the bendability of an Al–Mg–Si alloy is investigated using single-crystal specimens from the viewpoint of the shear band formation. The bendability and the formation of shear bands are clearly dependent on the crystal orientation, and ‹001›//ND-oriented specimens exhibit the highest bendability. The formation of denser shear bands is observed with a decrease in bendability. The shear bands behaved as the origin of the cracks and the propagation path. It is concluded that the inhibition of the formation of shear bands by controlling the orientations is very important to improve the bendability. Moreover, there exists a relation between the Taylor factor and the bendability because the bendability tended to decrease with an increase in the Taylor factor.

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To improve the cold formability of AZ31 magnesium alloy sheets, we investigate texture control by rolling and annealing. The texture ideal for forming close to random orientation was obtained by annealing at 773 K before and after isothermal rolling at 298–573 K. For the randomizing process, such a high temperature in pre-annealing was essential, whereas a slightly lower temperature was acceptable for final annealing, assuming a sufficiently long annealing time. The randomized sheet could be obtained in a wide range of rolling temperatures and reductions. It could also be produced easily with a standard mill without roll heating. The microstructure of the randomized sheet consisted of relatively homogeneous grains 25–30 μm large on average. In a 90 degree V-bending test, a well randomized sheet could be bent without cracking with a minimum bending radius per thickness R/t=1.4, which was about half of that in commercial AZ31D-O sheets, in spite of manganese content of over 0.6%.

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