STUDY OF THE MICROSTRUCTURE OF A COMMERCIALLY PURE ALUMINIUM SUBJECTED TO SEVERE PLASTIC DEFORMATION. PART I: MICROSTRUCTURE

摘要

Microstructure evolution with increasing severe deformation, via equal channel angular pressing (ECAP), was investigated in a commercially pure 1200 aluminium. A true strain of 8 was sufficient at producing sub-micrometer scale grains and very fine subgrains in the grain interior. The deformation process was documented and described through field-emission gun scanning and transmission electron microscopy techniques. The largest fraction of high-angle grain boundaries, after 8 ECAP passes, accounted for ~72 percent of all boundaries. The fine spacing resolution achieved by field-emission gun scanning electron microscopy allowed detailed statistical grain and subgrain evaluation of the deformed microstructure, while transmission electron inspections let to. appreciate and point out the very low-angle misorientation boundaries role within the microstructure refining -process. ECAP results were compared to the mechanisms involved in cold rolling. The use of FEG-SEM was of paramount interest essentially for the potentialities coming from the orientation image maps (OIM), which allows to directly detect the overall grained and subgrained structure. This type of analysis would require a time consuming procedures by using conventional TEM techniques. Thus, FEG-SEM constitutes a unique methodology for the volume evaluation of the perimeter of either subgrains and grains decorating the microstructure. As a counterpart, TEM seems to maintain the unique attitude for studies on the early stages of deformed microstructure such as the detection of cell and micro-bands boundaries whose typical disorientation lies in the range of 0.1-0.2 deg .