Equal Channel Angular Pressing Route Research Articles

Grain refinement mechanism analysis and experimental investigation of equal channel angular pressing for producing pure aluminum ultra-fine grained materials

Bulk ultra-fine grained (UFG) materials can be obtained by equal channel angular pressing (ECAP) process. Using our own commercial metal forming finite element code CASFORM/PC, ECAP process is analyzed numerically in this paper. The grain refinement mechanism is presented. The node mapping method is employed to realize the analysis of multi-pass ECAP process. Rules of acquiring the uniform deformation distribution of the final workpiece are put forward for pure aluminum material. The obtained results can offer valuable processing parameters and optimal processing routes of ECAP for producing UFG materials. Meanwhile, the microstructure evolutions of grain refinement mechanisms for different multi-pass ECAP processing routes are verified by using ECAP experiments and microstructure analysis. Through the numerical simulations and experimental studies, the uniformly deformed UFG materials with high angle grain boundary microstructure can be obtained by adjusting processing routes and parameters. The formation mechanism of nanostructure was given for the ECAP through studying the deformation behavior and dislocation's evolution. The process of grain refinement can be described as continuous dynamic recovery and recrystallization. From the viewpoint of the microstructure analysis, the grain refinement process is to control the dynamic balance of the generation and annihilation of the dislocations. From the viewpoint of the macro deformation analysis, the grain refinement process is to seek optimal processing routes.

Effect of ECAP routes on the specific features of the “end effect”

A geometric model is proposed which describes specific features of the displacement and distortion of the end regions of the samples upon equal-channel angular pressing (ECAP). It is shown that, upon some ECAP, the volume occupied by the end regions can be relatively large. In such cases, the arising structure will be characterized by a substantial inhomogeneity, especially in relatively short samples or when using a small number of ECAP passes.

Effects of the Number of ECAP Passes and ECAP Route on the Heterogeneity in Mechanical Properties across the Sample from Titanium VT1-0

Titanium VT1-0 was processed by four passes of equal-channel angular pressing (ECAP) using two routes, BC and C. Pressed samples had a square section with a side length of 8 mm. Mechanical properties at tension (tensile strength, conventional yield strength and elongation) were determined at 9 points across the sample using small-size specimens, 1.5 mm in diameter, cut out along the pressing direction. Heterogeneity in the mechanical properties across the sample was determined based on the value of the variation coefficient. One can observe that heterogeneity in the mechanical properties generally tends to decrease with the number of ECAP passes.

Scaling up of equal-channel angular pressing and its effect on mechanical properties, microstructure, and hot workability of AA 6061

Equal-channel angular pressing (ECAP) was performed on aluminum 6061 billets with different cross-sectional areas to study the effect of scaling up on the mechanical properties, microstructure, and the hot workability of the alloy. In this study, annealed AA 6061 was subjected to severe plastic deformation at room temperature by ECAP (Route B C), producing 12.5 mm (0.5 in.), 50 mm (2.0 in.), and 100 mm (4.0 in.) square billets. The mechanical properties and microstructure of as pressed alloy were examined as a function of the extent of deformation and the cross-sectional area of the billets. Also, hot workability was determined by forging industrial parts at various temperatures. Results indicate that the average grain size after ECAP is of the order of 0.5 μm. This grain refinement resulted in enhanced hot workability at 315 °C (600 °F); indicating applicability of ECAP processed material in the forging industry.

Microstructure and properties of pure Ti processed by ECAP and cold extrusion

Equal channel angular pressing (ECAP) has been used to refine the grain size of commercially pure (CP) Ti as well as other metals and alloys. CP-Ti is usually processed at about 400°C because it lacks sufficient ductility at lower temperatures. The warm processing temperature limits the capability of the ECAP technique in improving the strength of CP-Ti. We have employed cold extrusion following warm ECAP to further refine the grains and improve the strength of CP-Ti. Ti billets were first processed for eight passes via ECAP route B C, with a clockwise rotation of 90° between adjacent passes. They were further processed by successive cold extrusions to an accumulative reduction in cross-section area by 47 or 75%. This paper reports the surface quality, microstructures, microhardness, tensile properties, and thermal stability of these Ti billets processed by a combination of ECAP and cold extrusion.

Influence of ECAP routes on the microstructure and properties of pure Ti

Equal channel angular pressing (ECAP) is an innovative technique that can produce bulk ultrafine-grained (UFG) materials in product forms large enough for structural applications. It is well known that ECAP route, defined by the sequence of orientations of the billets relative to the die during the iterative ECAP passes, significantly affects the microstructural development of the work piece. Studies reported in the literature have so far focused on fcc metals such as Al and Cu. In this work, we have studied the influence of ECAP routes on the microstructures and properties of hcp commercially-pure Ti. Three ECAP routes, conventionally defined as B A, B C and C, were used to process the Ti billets. Surface quality, microstructures, microhardness, tensile properties, anisotropy, and thermal stability were studied. The route B C is shown to be the best route for processing hcp Ti.