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Research Papers

J. Eng. Mater. Technol. 136, 031001 (2014) ();   doi:10.1115/1.4027093

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.

Technical Brief

J. Eng. Mater. Technol. 136, 034501 (2014) ();   doi:10.1115/1.4026938

Thermally activated energy, which varies linearly with static recovered strain, is calculated from static recovery experiments of pure aluminum initially plastically deformed by strain-rate-controlled tensile tests up to 10% engineering strain at room temperature. The activation energy at the initial static recovery is 20 kJ mol−1, which is much less than that of pure copper and attributed to the dislocation annihilation by glide or cross-slip as well as higher stacking fault energy. Once dislocation annihilation processes are exhausted, more energy is required for subgrains to form and then grow. Eventually the recovered strain is slowed down and gradually saturated.

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