Analysis of non-equal-channel angular pressing scheme applied for obtaining magnesium sheet in cold state

Abstract

Deformation patterns of rolling, equal-channel angular pressing and non-equal-channel angular pressing were evaluated. It is noted that when rolling, it is difficult to transfer a circular section preform into a rectangular section with a small thickness. This problem cannot be solved using equal-channel angular pressing. In connection with this, it is proposed to use a non-equal-channel angular pressing pattern to study the cast structure of magnesium. An experimental procedure based on cold extrusion of cylinders with a diameter of 42 mm and a height of 40 mm is described. The strip at the outlet was 40 mm in width and 1 mm in thickness. The percentage reduction of the preform material determined by the ratio of areas was 96 % with a draw ratio of 17. The specific pressures on the punch at the beginning ofthe extrusion process were 1200—1300 MPa, and extrusion force was 1670—1800 kN. The preform was cut into lengths that were rolled at a room temperature into 50 and 10 pm thick foils without intermediate annealing. Rolling was carried out on the Duo mill with a percentage reduction of 12—20 % at an average speed of 0,1 m/s. 20 passes were performed with a total relative reduction of 95 % to make the 50 pm thick foil. The results of computer simulation by the finite element method demonstrated that the constant value of the deformation degree is achieved at a rather considerable distance from the front end estimated as 50 times the thickness of the strip. The deformation rate field was calculated to determine the configuration of the deformation center. Energy costs were estimated. As a result of the completed set of calculated and experimental work, it was possible to establish the following — it is possible to produce a thin sheet preform from a cylindrical cast magnesium blank in one operation at a room temperature. The sheet blank has a level of ductility sufficient for subsequent sheet rolling. The sheet blank obtained in the proposed process has a high level of plastic deformation elaboration created due to the forming pattern with the high level of elongation and shear deformation. Despite the high level of pressure that must be applied to create a comprehensive compression scheme taking into account the lack of the need to heat the preform, energy costs are no higher than in traditional treatment processes.