Effect of Fe content on ductility and bendability of AA5754 and AA6111

The ductility and bendability of AA5754 (0.08 and 0.3 wt% Fe) and AA6111 (0.06 and 0.68 wt% Fe) automotive sheets have been investigated as a function of iron content. A significant decrease in reduction of area was observed for both alloys with an increase in the iron level. The low iron containing AA5754 sample showed cup-and-cone type failure whereas the high iron alloy failed in shear mode caused by void sheeting. In contrast, both the low and high iron containing AA6111 alloys failed in shear mode caused by void sheeting. AA5754 alloys have adequate bendability in the annealed state and can be formed without causing failure. The low iron containing AA5754 alloy showed development of surface instability in the form of small undulations on the tensile surface of a bent sample. This phenomenon becomes more prominent on pre-straining the samples using cold rolling. Similar topography has been observed to occur on the tensile free surface of the low iron containing AA6111 alloy. The high iron containing alloy has shown severe damage in the form of either deep grooves or cracks which run along the bend axis. In-situ bend tests in a scanning electron microscope revealed the development of shear bands and damage at the iron rich particles from surface imperfections. Shear bands and cracks propagate at about 45° to the maximum tensile direction where shear stress is maximum. These led to drastic reduction in the bendability of both AA5754 and AA6111 alloys.