Effect of Copper Content on the Bendability of Al-Mg-Si Alloy Sheet

Abstract

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 quench rate and microstructure on bendability of AA6016 aluminum alloys

“…A likely explanation is that the onset of cracking is due to textureinduced strain localization enhanced by the presence of large intermetallics particles. This explanation is consistent with the usual view that considers cracks to be initiated around large intermetallics particles within shear bands that form while these alloys are subjected to bending (see Introduction) [2,3,[5][6][7]19,21,23,26,36,37]. Neither grain structure nor intermetallic particles being influenced by the cooling rate, this is consistent with present data.…”

“…Their presence can be reduced with increased solution treatment time [25] or subsequent cooling rate [4,26]. No clear correlation between bendability and the type and proportion of grain boundary (GB) precipitates is established; some authors consider that these have no effects on bendability [6]. There are data to show that precipitation during natural (room-temperature) ageing of T4 alloys has an influence on bendability, causing it to decrease during storage [19,22].…”

“…AlFeSi intermetallics favour crack initiation [1][2][3][4][5][6][7]: during deformation, intermetallic particles situated along shear bands initiate voiding which, in turn, promotes shear crack formation. These larger intermetallic particles are generally formed during homogenization of as-cast ingots and do not dissolve when the alloy is further heat treated.…”

Microstructure controlled bending response in AA6016 Al alloys

“…In this case it is considered that the bendability of aluminium alloy sheets is directly governed by the combined effect of micro-voids formation around large secondphase particles, strain localization and propagation of macroscopic shear bands [10][11][12]. Lievers et al [13] confirmed that the shear bands and void damage development play co-operative role in promoting ductile fracture at the outer free surface during bending.…”

Strain localization and damage mechanisms during bending of AA6016 sheet

“…Bending is important in the shaping of complex parts, and it is also critical in the joining of outer skins to inner sheet panels by hemming. Appropriate strength levels for automotive aluminum panels are achieved by a combination of alloy composition and thermo mechanical treatment [1,2], and several experimental studies concern the influence of alloy composition on bend performance of Al 6xxx automotive sheet [3][4][5][6]. The bendability has been shown to decrease with increasing copper, iron and Si content.…”