LOCAL ANALYSIS OF PLASTIC DEFORMATION IN ECAP AND ECAR PROCESSES

Chem. Listy 106, s464s467 (2012) LMP 2011 Regular Papers s464 TIBOR KVAČKAJ a , RÓBERT KOČIŠKO a , and ANDREA KOVÁČOVÁ a Department of Metals Forming, Faculty of Metallurgy, Technical University of Košice, 042 00 Košice, Slovakia [email protected] Keywords: equal channel angular pressing, equal channel angular rolling, finite element method, microhardness 1. Introduction Ultrafine-grained (UFG) metallic material has re- ceived considerable research interest because it exhibits high strength along with good ductility and toughness. Recently, as one of the prominent methods to produce UFG bulk 1-5 and powder 6-8 metallic material, equal channel angular pressing (ECAP) has been studied extensively. The ECAP process (Fig. 1a) is a method that involves large shear plastic deformation in a workpiece by moving through a die containing two intersecting channels of iden- tical cross-sections that meet at a predetermined angle (Ф). The process can be repeated extruding the sample through the same matrix. Several papers evaluated the distribution the effective strain distribution through the cross section of the sample after the ECAP process based on finite element method (FEM) modeling 9,10 . The heterogeneity of non deformation can be reduced by the axial rotation of the sample between passes. Thus the slip planes are activated. ECAP process runs by a discontinuous process, causing a limiting of a maximum lenght of processed sample, which is about 100 mm. Recently a new continuous shear deformation process, which has several names in the literature as “a continuous ECAP process”, "continuous conﬁned strip shear- ing (C2S2)" 11 or equal channel angular rolling (ECAR) 12,13 was developed. This process can be applied to strip or profile form of materials. The sample is extruded through a matrix with upper guide roll and lower feeding roll, as shown in Fig. 1b. In this process friction plays a major role, which must provide a frictional force to prevent spin on the material in the feeding roll. Several authors published the effective strain distribution through the cross section of the strip 14 and sheet 15 after the ECAR process based on FEM modeling. ECAR process is compared to ECAP much more difficult to oper- ate the forming process, therefore this technology is to be reviewed. This work deals with local comparison of plastic deformation in ECAP and ECAR process after the first pass, on two experimental materials, OFHC copper and alluminium 99.5 %. 2. Experimental material and methodics For the experiment two materials with different strain hardening were used. Oxygen-free high conductivity (OFHC) copper and alluminium 99.5 %. Flow stress is characterized by the Hollomans´s equation σ = K . ε n , where: σ - flow stress, ε - strain and n - strain hardening exponent. Flow stress for copper is σ = 460.ε 0.38 and for alluminium is σ = 108.ε 0.22 . The initial microhardness for the Cu = 117 HV1 and Al= 36 HV1. Both materials were processed by one pass using ECAP and ECAR technology. The ECAP was realized by hydraulic equipment at room temperature, which makes it possible to produce the maximum force of 1 MN. The die channel angle was Ф = 90° with diameter 10 mm. Extrusion speed was 5 mm min –1 . The length of the sample was 100 mm. The ECAR was carried out on 210 DUO rolling mill at room temperature. The groove of feeding roll has a di- mension of 6 x 6 mm. Output channel has dimensions 6 6.5 mm. Angle between feeding roll and output channel is Ф = 90°. Angular velocity of rolls were 0.052 rad/s, corresponding to extrusion speed 5 mm s –1 . Stress-strain analysis was performed using the com- mercial software product Deform 3D. Geometric dimensions and process variables of ECAP and ECAR process were simulated under laboratory conditions listed above. Samples for ECAP and ECAR were defined as a rigid- plastic object. Flow stress was defined according to the above Holloman´s equations. All other components of ECAP and ECAR equipment (die, ram, rolls) were defined as perfectly rigid objects. Local heterogeneity of plastic deformation in the cross section of smaple after ECAP and ECAR processing was detection by measuring the microhardness as a func- tion of strain hardening. The microhardness measurements LOCAL ANALYSIS OF PLASTIC DEFORMATION IN ECAP AND ECAR PROCESSES Fig. 1. Scheme of: a) ECAP and b) ECAR method Φ Die workpice F Die Guide roll Guide roll Φ workpice r R

LOCAL ANALYSIS OF PLASTIC DEFORMATION IN ECAP AND ECAR PROCESSES

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