Equal channel angular pressing（ECAP）

as one of the most effective methods for producing ultra-fine grain materials（UFG）

whose principle is that through pressing the billet in the die with two channels intersecting at an angle repeatedly

high shear strain is imposed on the sample

and thus the grain size is refined.However

experiments show that cracking or fracture usually occurs in the vicinity of upper surface of the extruded specimen even only after a few passes with conventional die（90°）.The tensile stress occurs in the vicinity of upper surface of the specimen in the severe plastic deformation zone

which increases the crack and fracture tendency of the specimen and impedes the further ECAP processing.2A12aluminum alloy was tested by ECAP.The results reveal that in the Crouth four passes

extruding effect exhibits desirable

and the grain refinement is improved

where elongation is increased by 10.3%

and maximum hardness is increased by 46.4%.