The effects of the copper content on the bendability of Al-Mg-Si alloy T4 sheets were investigated. The Al-Mg-Si alloys with less than 0.01mass%Cu, 0.4mass%Cu and 0.8mass%Cu were prepared, and the time of solution heat treatment was changed to obtain different dispersion conditions of the second phase particles and to obtain different shear band formation conditions by bending. For the samples with less than 0.01mass%Cu and 0.4mass%Cu, no cracks were observed during the bending. For the sample with 0.8mass%Cu, the maximum depth of the crack by bending increased with the time of solution heat treatment up to 75 seconds, and then decreased over 75 seconds. The second phase particles decreased by increasing the solution heat treatment time, while the formation of shear bands by bending increased by increasing the solution heat treatment time and the copper content. The cause of the occurrence and the propagation of cracks by bending are considered to be the combined effect of the shear band formation across some grains and the micro-voids formed around the second phase particles. Improving of the bendability requires a decrease in the size and number of the second phase particles and/or reduced shear band formation during the bending.

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.

Lap shear dissimilar joints between aluminium (Al) alloy, A6061-T6, and stainless steel, type 304, were fabricated by adhesive bonding. Three Al plates with different thicknesses were used to investigate the effect of the Al plate thickness on the tensile-shear properties, namely the effect of bending stiffness of Al plates. The maximum tensile-shear loads increased with increasing Al plate thicknesses. The fracture through the adherent (cohesive fracture) occurred when the Al plate was the thickest, while the interface fracture between Al plate and adherent appeared on the fracture surface with decreasing Al plate thickness. Fatigue strengths also increased with increasing Al plate thickness. When the fatigue strengths were normalized by the tensile strengths, the effect of the plate thickness became negligible. FEM analyses revealed that the stress concentration at the edge of adhesive on Al side decreased with increasing Al plate thickness, which could be related to the dependence of tensile and fatigue properties on the Al plate thickness.