A demanding application for aluminium in the automotive industry is that of body panels. These applications require bending in various degrees, especially at the edges. The solution heat treatment and subsequent aging of aluminium alloys dramatically alters the mechanical properties of these alloys compared to their un-aged state and the bendability of sheet metal is critically dependent on the work hardening behaviour, which for Al means it is critically dependant on its aging state.
Investigations were performed into the aging response of two wrought aluminium alloys, A12011 and A16061 when tested in tensile and bending deformation. Comparisons were then made between the results of each aged state.
Solution heat treatment and subsequent aging time significantly effected the bending behaviour of these wrought aluminium alloys. When bent under a 75mm displacement, it was found that aging did not have a dramatic effect on the radius of curvature of the A12011 specimens. The radius of curvature gradually increased with aging time until failure occurred in the over-aged state. This was due to an incremental increase in the work hardening rate in each aged state, which lead to a spreading of the plastic hinge. Severe surface roughness and cracking was observed in the peak-aged specimens. From this data, the aged state with the most acceptable surface finish and radius of curvature finish for A12011 is the under-aged state.
Aging had a significant effect on the radius of curvature of the bend in the A16061 samples, causing “kinking” in all of the aged states. This data gives the perception that the aging of A16061 results in a decrease in the work hardening rate of the alloy, however, work hardening rate must be seen with reference to the current yield strength (obtained from the tensile test) which proves this to be untrue. In addition to the kinking, cracking and surface roughness was observed in all aged states. The results suggest that A16061 samples should not be aged when used for bending applications, however, the energy absorption of these samples in their un-aged state is far too low. Therefore, in bending applications, this alloy should be aged after it has been bent into shape.