The plastic deformation induced surface roughening mechanism of aluminum sheets is experimentally investigated. Specimens used in the study have grain sizes varying from tens of microns to millimeters. The roughnesses of the specimens’ free surfaces are measured during plastic deformation by means of a mechanical stylus type profilometer with a tip radius of 5 microns. Observations show that plastic deformation roughens a free surface mainly by introducing slip bands within individual grains and relative rotation among grains. The average grain rotation and grain size are found to be the dominant contributor to the surface vertical characteristics such as the root-mean-square roughness. The surface horizontal characteristic such as the correlation length is found to be mainly determined by the average grain size. Based on the observations and some analysis, a model is advanced for the explanation of the phenomenon that the root-mean-square roughness is proportional to the magnitude of plastic deformation and average grain size.

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