Characterizing the Hemming Performance of Automotive Aluminum Alloys With High-Resolution Topographic Imaging

We used high-resolution quantitative surface analysis to evaluate the surfaces of two aluminum automotive closure panel alloys, which were bent to a 180 deg angle in a simulated hemming test. Maps of the displacements normal to the sheet were superimposed on the topographies to correlate the location of the maximum displacements and the surface morphology. While the alloys had similar mechanical properties, quantitative analyses yielded considerable differences in the deformed surface morphologies. One alloy had a greater density and broader size distribution of constituent particles, which increased the likelihood for particle decohesion. This resulted in large surface displacements that were uncorrelated with the underlying microstructure. While no splitting was observed in either alloy, large uncorrelated surface displacements could indicate the presence of short surface cracks.