Surface roughening in metal forming processes

The goal of this dissertation is to investigate the phenomenon of workpiece surface roughening in metal forming processes under plastic deformation. The roughening of AL 1100-H14 and AL 5052-0 aluminum alloys were investigated in rolling and in a tensile test. Observations of micro-morphology of the tested specimens revealed surface roughening mechanisms. Mathematical modeling was carried out based on the results from the micro-morphological observation. Micro-topographical and micro-mechanical characterization of the test materials were conducted and quantitative results were used in the models. The results of the modeling prediction were compared with experimental measurements.; Evolution of surface roughening and the micro-structure of the roughened surface under plastic deformation were investigated by SEM and TEM observations. Two types of roughness features were found and categorized from their surface micro-morphology. (a) Trans-granular fissures leading to a "cobble stone" appearance are the principal features of the roughened surface. (b) Intra-granular slip bands are superimposed on the "cobble stone" pattern.; Upper-bound models (with and without a velocity discontinuities) for surface roughening on a workpiece undergoing plastic deformation were developed to simulate the trans-granular fissures. A slip band model was developed to simulate the intra-granular transverse fissures.; A comparison of the results of the upper-bound models showed that "cobble stone" type features were the major source of the roughness of the deformed surface. Micro-topographic measurements from AFM and micro-mechanical characterization of the test materials using an ultra-micro indentation test provided quantitative data for the mathematical models. Theoretical predictions of the final surface roughness average with plastic strain show excellent agreement with experimental measurements on AL 1100-H14 and AL 5052-0 in tension tests and on AL 5052-0 in rolling. Experimental measurements of the roughness in rolling AL 1100-H14 aluminum were smaller than predicted by the theory. This may be due to dynamic recrystallization.