Trimming and sheared edge stretchability of automotive 6xxx aluminum alloys

Edge quality produced by shearing processes often leads to reduced material formability which was observed in multiple studies and summarized in the reference literature. The intention to make the sheared edge performance more predictable has motivated the development of several experimental techniques such as the hole expansion test and the tensile test with one side of the sample sheared in various cutting conditions. The paper presents a review of published results for both of these techniques and illustrates very limited research dedicated to sheared edge performance of aluminum alloys. The experimental study was performed on three broadly used in automotive industry 6xxx serious aluminum alloys which have similar mechanical properties and chemical composition with some variation in processing regimes and individual elements quantities. The effects of cutting clearance on longitudinal, transverse and diagonal orientations of the trim line relative to the rolling direction were discussed for all three alloys. The results of standard tensile test of all three materials were very similar with rather small difference in work hardening and almost no difference in total elongations measured by an extensometer. Measurements of elongations as a result of stretching of samples along orthogonally trimmed sheared surfaces indicated that the increase of the cutting clearance above 5% for Alloy 1 and above 15% for Alloy 2 usually leads to formation of burrs and reduced elongations of trimmed samples before fracture occurs. The effect of cutting clearance on sheared edge stretching performance for Alloy 3 is significantly less pronounced than for Alloys 1 and 2, which makes Alloy 3 very attractive for exterior panel automotive applications in which significant stretching of sheared edge can be anticipated. Detailed discussion of mechanism of blank separation during trimming process was based upon the results of 2D numerical simulation and interrupted trimming process with partially propagated cracks.