Tadashi Minoda

Effect of copper content on the bendability of Al-Mg-Si alloy sheet

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.

Influence of Iron Content on the Mechanical Properties of AA6016 Alloy Sheet

The influence of the iron content from 0.1 to 1.0 mass% on the mechanical properties of AA6016-T4 sheets was investigated. The amount of the Al-Fe-Si second phase particles increased with the iron content, thus the solute silicon atoms decreased. Increasing of the Al-Fe-Si particles lowers the bendability, while decreasing of the solute silicon atoms lowers the paint bake response (PBR) and improves the bendability. The bendability of the samples then became the worst at the 0.5 mass% iron content, while it at 0.8 and 1.0 mass% became better or the same as that at 0.5 mass%. The increasing of the silicon content in the 1.0 mass% iron content alloy improved the PBR and lowered the bendability.

Mechanical properties of 7475 aluminum alloy sheets with fine subgrain structure by warm rolling

The effect of transition elements on grain refinement of 7475 aluminum alloy sheets produced by warm rolling was investigated. The alloy which contains zirconium instead of chromium showed ultra fine structures with stable subgrains after warm rolling at 350 °C, followed by solution heat treatment at 480 °C. The average subgrain diameter was approximately 3 μm. It became clear that zirconium in solution has the effect of stabilizing subgrains due to precipitation of fine Al3Zr compounds during warm rolling. On the other hand, chromium-bearing compounds precipitate before warm rolling and they grow up to relatively large size during warm rolling. The warm rolled sheets with fine subgrains have unique properties compared with conventional 7475 aluminum alloy sheets produced by cold rolling. The warm rolled sheets solution heat treated had subgrain structures through the thickness with a high proportion of low-angle boundary less than 15°. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional 7475 aluminum alloy sheets. As the most remarkable point in the warm rolled sheets, the high Lankford (r) value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed β-fiber textures, especially with the strong {011}«211» brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low-angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.

Influence of chemical composition on aging property of 7N01 aluminum alloy

The influence of the room temperature pre-aging (RTPA) conditions on the strength of 7N01 aluminum alloy in T6 temper was changed by the zinc and magnesium contents. When both the zinc and magnesium contents were the lowest and the RTPA was omitted, the strength became the lowest because the aging rate during artificial aging decreased and a non-homogeneous precipitation of the η′ phase occurred. On the other hand, the η′ phase became finer and the strength in T6 temper became higher as the RTPA was longer and higher. Also, the two-step artificial aging resulted in a higher strength. It was considered that the GP(I) zones, which formed during RTPA, dissolved and the GP(II) zones formed during heating process of the artificial aging. Because the GP(II) zones were the precursor to the h9 phase, the strength became higher by the RTPA and the two-step aging. Furthermore, the influence of RTPA on the strength in T6 temper decreased with the increasing zinc and magnesium contents, and it almost disappeared when both the zinc and magnesium contents were maximum values. It was considered that the aging rate increased, and the GP(I) and GP(II) zones adequately formed during the heating stage of the artificial aging process because the solute atoms of the zinc and magnesium were sufficiently present.