A. Kováčová

Influence of SPD by ECAP on Cu Properties

Equal channel angular pressing (ECAP) is a material processing method for developing an ultrafine-grained (UFG) structure by introducing severe plastic deformation (SPD) in a bulk material with no changes in its cross-section. Numerous analytical and numerical studies on equal channel angular pressing have been performed in recent years. The present work focuses on the effects of die geometry width is defined by the angle between two channels Φ, angle on outer corner of die Ψ (or radius R) and angle within internal corner (or radius r) of die on average effective strain after one pass route. Next, there are analyses of strength properties, plastic properties, fracture mechanism, as well as analyses of Cu structure evolution after SPD by ECAP technology, in the paper. The sixteen passes through the ECAP matrix were realized using route C. The following experimental results and their analyses, the biggest increase of strength and microhardness was proved already after 4th pass. Valuation of fracture surfaces shows that after 12th pass plastic fracture is transformed from transcrystalline ductile mixed fracture. After 4th pass, the avarage grain size decreased from initial approximate size 7 µm to 200 nm, whereby the average grain size was changeless after subsequent deformations. Possible mechanism of high-angle boundary nanograins evolution consists of formation of cell structure, subgrains that transform with the increase of deformation into nanograins with big-angle misorientation.

A COMPACTING PROCESS OF THE EN AW 6060 ALLOY

This study reports on an investigation of factors affect the process of compacting Al chips which are used to direct scrap processing through the forward extrusion method. EN AW 6060 chips of different geometry and types were mainly used as the experimental material. The chips were compacted in a die with a vertical channel (10.3mm in diameter). To provide a range of processing conditions, three different weights were selected and compacting was performed under five, different compacting pressures. The movement of the chips within the die during compacting was analysed through numerical simulations using Deform 2D software. Study of the compacting process optimal parameters for increasing the density and enhancing the density distribution were defined. The results from our study clearly show that optimal conditions are obtained when the proportion of D/h is 1/1.1. Moreover, it was recognized that in the process of small chips compacting, there was obtained lower density than in the case of large chips.

The Influence of Thermo-Plastic Processes on Materials Recovery

The influence of thermo-plastic processes through methods of severe plastic deformations (SPD) and rolling carried out at ambient and cryogenic temperatures on recovery of two materials was investigated. The aim of this study was to insert strains to materials having middle and high stacking fault energy (SFE) in ambient and cryogenic temperature conditions, respectively and subsequently, through DSC method, to observe an influence of the storage energy on structural recovery of materials. As experimental materials were used oxygen free high conductivity copper (OFHC Cu) and C-Si steel which represent materials with middle and high stacking fault energy (SFE), respectively. The OFHC Cu was subjected to equal channel angular rolling (ECAR) by seven passes. ECAR is a method belonging to a SPD group. It was shown, five ECAR passes have a significant effect on material properties. The rolling performed at cryogenic temperatures using a laboratory duo rolling mill was carried out only once. This study implies that a recovery process (characterized by the mobility of structural defects) starts as follows: for OFHC Cu without ECAR and processed by 5th ECAR passes: 0.31·Tmelt and 0.19·Tmelt, respectively, for C-Si steel processed by cryorolling: 0.095·Tmelt.

Cockcroft-Latham Ductile Fracture Criteria for Non Ferrous Materials

The determination of ductile fracture criteria as well as friction coefficient, stress-strain curves, constants for Hollomons equation and a material workability based on analytical methods as a forming limit diagram, a normalized Cockcroft-Latham criteria (nCL)) ring and compression tests for two materials based on aluminum and copper alloys were carried out. A calculation of nCL criteria on the basis of a compression test and numerical simulations was made. The critical values nCL criteria resulting from compression test were determined. Prediction of nCL criteria by numerical simulations were confirmed by laboratory compression tests. The values obtained from numerical simulations and compression tests for both materials show a good coincidence in results.