Cold Equal Channel Angular Pressing Research Articles

On achieving superior strength for Al–Mg–Zn alloy adopting cold ECAP

The current work aimed to investigate the effect of equal channel angular pressing (ECAP) on AA7075-T6 aluminum alloys, which were successfully processed at room temperature with six passes. Achieving sound microstructures and better mechanical properties due to cold ECAP were investigated. It was found that ultra-fine grains that owned an average grain size of about 103 nm were successfully achieved after six cold ECAP passes. Grain refinement, precipitation, and dislocation after ECAP have been evaluated. The results showed the η phases were fragmented with an increased density, and the η′ phases were significantly formed during the first ECAP pass. Consequent processing up to 6 passes presented that the GP zones have not been detected due to the transformation to η′, leading to the maximum η’ precipitate density of 7.1x1015 m-2 with the average size of 5.5 nm, while a very little η phases still detected after the redissolution. Besides, the microhardness of the adopted alloy was gradually increased. The yield strength was remarkably increased to 500 MPa with a significant improvement of 70.6% after a single pass. By increasing the passes number to 6, the strength of the ECAPed alloy was significantly improved to the maximum ultimate tensile strength of 647 MPa and yield strength of 605 MPa.

UFG Microstructure Processing by ECAP from Double Electron-Beam Melted Rare Metal

High purity (99.99, wt %) niobium ingots were received by double electron beam melting technology. The specimens of pure metals with cast microstructure were processed using cold equal-channel angular pressing (ECAP) followed by a heat treatment at around 1080 °C in vacuum furnace for 2 h. Shear bands and microstructure evolution was studied in shear region at first pass and at next passes of ECAP. Microstructure processing characterization was performed using light optical and field emission scanning electron microscopy. Accompanied to microstructure the changes of mechanical properties were determined by micro- and universal hardness testing. The shear bands forming, evolution of large crystals to elongated laminar and dislocation fine-grain structures during processing was characterized and discussed in view of metal hardening-softening and viscoplastic behavior under subsequent hard cyclic straining.

Formation of a submicrocrystalline structure in St10 and 08R steels during equal-channel angular pressing

The effect of cold equal-channel angular pressing (ECAP) on the structure and properties of low-carbon St10 and 08R steels in the initially ferritic-pearlitic and bainitic states is studied. Directly after ECAP, only a partially submicrocrystalline structure with a grain size of 150–300 nm (depending on alloying and the initial state) can be obtained. Along with a granular structure, a subgrain and/or cellular structure, including an oriented structure, are observed. The finest structure forms in a boron-containing 08R steel with a structural-element size of 190 nm. The strength of the 08R steel subjected to cold ECAP (σu = 805–1235 MPa) corresponds to a hardware strength class of 8.8–12.9. The strength of the deformed St10 steel is close to a strength class of 8.8.

Structure formation, phase transformations and properties in Cr–Ni austenitic steel after equal-channel angular pressing and heating

It is shown that cold equal-channel angular pressing (ECAP) of corrosion resistant austenitic 0.07%C–17.3%Cr–9.2%Ni–0.7%Ti steel leads to formation of submicrocrystalline structure: generally oriented subgrains and cells with separated grains (100–250 nm in size). The steel samples 20 mm in diameter and 80 mm in length were subjected to ECAP at room temperature for four passes. The angle between the channels was 120°. ECAP promotes the martensitic transformation which becomes more active only after four passes, leading to the formation of 45% martensite. During heating, the fraction of high-angle boundaries and the volume of austenite are increased, and the microstructure becomes more equiaxed. Submicrocrystalline structure with grain size 150–250 nm and 80% of austenite was obtained upon heating to 550 °C. Such structure exhibits a substantial strain hardening (yield strength 1090 MPa relative to the initial with 320 MPa) and an elongation of 12%.

The Effect of Cold Equal Channel Angular Process on Texture of Magnesium Alloy (AZ31)

In the present study, we have attempted to refine a microstructure of conventional AZ31 magnesium alloy using a new combination process including hot extrusion followed by a cold equal channel angular pressing (ECAP). ECAP die was specially designed with an inner die corner angle of 135 degree, the fillet angle of 45 degree and dimensional thermo-coupled elastro-plastic material model in order to understand the change of stress and strain of the deformed material after a cold ECAP. ECAP for the AZ31 alloy, which was extruded in the extrusion ratio 20 to 1 and heat-treated at 623K, was successfully carried out at room temperature. The uniform shear band obtained from experiment was well matched with the zone of effective strain more than 0.533 estimated from calculation. On the basis of the results, it is suggested that the room temperature ECAP makes microstructure to be refined and the basal plane to be rotated slightly from extrusion direction to axis direction. Compressive yield strength of AZ31 alloy can be enhanced up to twice in applying ECAP process. Hall-Petch relations do not fit to the experimental data This can be ascribed to the texture effect. Room temperature ECAP process is very promising in improving mechanical properties of AZ31 alloy in terms of grain refinement and texture control.

Application of a Cold ECAP to Magnesium Alloy (AZ31) by a Combination of Extrusion Process

It is well known that magnesium alloys have difficulties in room temperature formability because of their HCP structure. As a basic approach to enhance a cold formability, a new combination process including an extrusion followed by a cold equal channel angular pressing (ECAP) was attempted. ECAP die has an inner die corner angle of 135 degree, the fillet angle of 45 degree and thickness of 5mm. A finite element analysis with a three-dimensional thermo-coupled elasto-plastic model was also carried out to understand the change of stress and strain during ECAP. Experiments showed that the AZ31 alloy, which is extruded at a ratio of 20 and is heat-treated at 350°C, was successful in a cold ECAP. From the simulated results, it was found that the effective strain gradually decreased from the inner die side (0.533) to the outer die side. This was confirmed by the analytical analysis via von Mises criterion. Furthermore, it also matched well with the experiments, which showed a uniform shear deformation band. It was also interesting to note that compressive yield strength was drastically increased, which is caused by the occurrence of numerous twins spread across the materials during a cold ECAP.