Analysis of the billet deformation during equal channel angular pressing

The purpose of equal channel angular pressing (ECAP) is obtaining the ultra-fine grained materials. For practical application, it is important to understand the billet deformation behavior which is affected by many parameters, such as geometry, friction between billet and mold, corner gap shape, back pressure and back pressing plunger shape. Because most deformation occurs during the passage at the mold corner, finite element analysis and optical observations of the square-grid-distortion engraved on the surface of the billet were performed at the mold corner. The effects of external force (friction, back pressure) and mold corner shape on billet deformation were studied to improve the quality of the ECAP process. A new index factor was defined and suggested from the analysis of billet deformation during ECAP to get the uniform microstructure. Variation of the suggested index factor is also studied to account for the effects of material properties and back pressure produced by friction and back pressing plunger. In this study it showed that the corner shape was one of the strongest factors to be controlled for the improvement of ECAP process.