Coupled Thermo‐Mechanical Analysis of Severe Plastic Deformation for Producing Bulk Nanostructured Materials

Abstract

Nanostructured metals, in which the grain sizes are in the range of 1 to 100 nm, have superior mechanical, unique physical and chemical properties. Nanostructured metals with bulk size have a wide range of engineering applications. [1] Bulk nanostructured metals can be produced by severe plastic deformation. [1,2] Among the various severe plastic deformation methods, equal channel angular pressing (ECAP) is the most promising one and therefore it has attracted increasing research attention in the last few years. As the grain refinement is directly related to the amount of plastic deformation, it is very important to understand the phenomenon associated with the strain development in ECAP. Finite element method (FEM) has been used by some researchers [3±5] to study the deformation behavior, strain and stress in the workpiece, in order to get a better understanding of the ECAP process and to optimize the process conditions. However, in these studies the isothermal conditions were assumed, which is only correct for very low pressing speed. For high pressing speed, the deformation heating will result in very obvious temperature rise in the workpiece. The temperature rise will change the flow stress of the material, and thus influence the deformation behavior of the workpiece during ECAP. In addition, the temperature rise will change the recrystallization temperature, and thus affect the grain size formed. [6] In this article, we present the coupled thermo-mechanical finite element analysis of ECAP to study the temperature rise and deformation behavior in the workpiece. We investigated the effects of pressing speed, pressing temperature, workpiece material and die geometry on the temperature rise and flow behavior during ECAP.In our finite element model, two-dimensional plane strain and heat transfer models are used with the workpiece dimensions being 6010 mm, The heat generation rate due to plastic deformation, q p , is calculated by the following equation:where e is the plastic strain rate; r is the flow stress; g p is the fraction of plastic deformation energy transformed into heat, which is taken to be 0.9. [7] Two aluminum alloys of Al-1 %Mg and Al-3 %Mg are used as the workpiece materials. For severe plastic deformation with high strain rate and big temperature rise, the correct material constitutive model used in the simulation is crucial to obtain accurate simulation results. The material model must be able to consider the multiplication effects of strain, strain rate, and temperature on the flow stress. Therefore, the Johnson-Cook (JC) model [8] is used in the simulations.In the JC model, the flow stress is expressed as:where e is the equivalent plastic strain; e is the strain rate; e 0 is a reference strain rate; T r is a reference temperature; T m is the melting temperature of the material; A, B, C, n, and m are material constants.In the simulations, T r and T m are taken to be 286 K and 893 K respectively. e 0 is taken to be 3.310 ±4 s ±1

Equal channel angular extrusion (ECAE) of intermetallics

“…The remaining 10% width has lower strains in FEA, and lower hardness values in experimental. The uniform hardness and strain distribution were achieved in the current study due to the usage of lower outer corner angle ECAE die, and the results also show better correlation between FEA strain homogeneity and the hardness measurements, compared to earlier studies[76,87]. Effective strain and Vickers hardness distributions across the width (A-B) of the copper after single pass ECAE.…”

Equal Channel Angular Pressing Die Outer Corner Angle Influence on Flow and Strain Homogeneity

“…1) in the flow plane of the deformed samples. To analyze the strain homogeneity, most of the earlier studies [10,11,[13][14][15][16][17][18][19][20][21][22][23]25,26] considered only the effective strain variation across the width of the samples in the flow plane. The combination of shear and effective strain variations in a single plot gives the most useful information regarding the deformation behavior, stress-strain states, and thus the strain homogeneity.…”

Study of deformation homogeneity in the multi-pass equal channel angular extrusion process

“…Previous simulation studies [13] conducted found that the highest and most uniform strain distribution is achieved when the half-angle between the two die channels (Φ) and the angle at the outer intersection of the channels (Ψ ) are 90 • and 0 • , respectively (as shown in Fig. 3).…”

“…Finite element simulation of the equivalent plastic strains accumulated by ECAE process of Al-1%Mg and Al-3%Mg carried out using a commercial software, ABAQUS showed that ECAE carried out with a 90 • die produces the highest and most uniform strain distribution in the workpiece [13]. Therefore, it is necessary to investigate the effects of multi-pass ECAE processing using a 90 • die.…”

“…This allows materials to be deformed for many passes to very high plastic strains. The strain in ECAE extruded materials are accumulated with increasing number of ECAE passes [13]. As a result, the mechanical properties and structure of materials processed by ECAE are affected by the number of passes.…”