Equal Channel Angular Pressing Technique Research Articles

Evolution of Strain in Multipass Hybrid Equal Channel Angular Pressing Using 3D Finite Element Analysis

Severe Plastic Deformation (SPD) is well known process for producing nanostructured material from coarse material. Present paper is an effort to integrate the two well known SPD techniques Equal Channel Angular Pressing (ECAP) and Twist Extrusion (TE) to develop a new Hybrid ECAP (HECAP) technique that can produce nanostructured material more economically. In this technique, the specimen is subjected to both ECAP and TE in the same die setup. Finite Element (FE) modeling of metal forming processes has become an important tool for designing feasible production processes, because of its unique capability to describe the complex geometry and boundary conditions. FE Modeling of the above hybrid process is attempted in FORGE. The simulation results clearly depict the change in equivalent strain in the entire specimen on account of this process upto four passes. A comparison is made between FE results of simple ECAP and HECAP upto four passes. The study indicated that equivalent strain is much higher in case of HECAP in comparison to ECAP for same friction conditions. Also, the study is extended to analyse the effect of friction, channel angle and forging force on equivalent strain using current FE model. HECAP opens new possibilities for improving equivalent strain in same number of passes as compared to ECAP. This study is expected to contribute in forming UFG materials that are useful for automobile and aerospace industries.

Equal Channel Angular Pressing of Al-SiC Composites Fabricated by Stir Casting

Stir casting method was used to produce conventional metal matrix composites (MMC) with fairly homogenous dispersion of reinforcement material. Commercial pure aluminum and silicon carbide particles (50 μm) were selected as matrix and reinforcement materials respectively. The matrix was first completely melt and kept constant at 750°C. Then SiC powder preheated to 800°C was added during stirring action. No wetting agents were used. The melt mixture was poured into a metallic mold. The composite contents were adjusted to contain 5% and 10% SiC. The as-cast composites were processed by Equal Channel Angular Pressing (ECAP) route A. The microstructure and mechanical properties were studied. Results indicated that as cast AlSiC composites can be successfully fabricated via a cheap conventional stir casting method, giving fairly dispersed SiC particle distribution and having low porosity levels 3.6%. The mechanical properties have improved compared to as cast composites. ECAP technique has greatly reduced SiC particles from 50 to 3 μm. After the first ECAP pass, yield strength has almost twice its value in the as cast composites. The maximum yield of 245 MPa obtained after 8 passes is almost four times the corresponding values of the as cast MMC composites. Hardness has also increased to 1.5 times its value in the as cast composites after one ECAP pass. The maximum hardness of 71 HRB obtained after 8 passes, which is almost 3.5 times the corresponding values of the as cast MMC composites.

The effect of equal channel angular pressing on the mechanical and magnetic properties of 09Γ2C steel

The physical and mechanical properties of 09Γ2C steel that was subjected to strengthening by intense plastic deformation using the method of equal channel angular pressing (ECAP) are studied. An unambiguous interrelationship between the magnetic (coercive force, maximal permeability, Barkhausen magnetic noise parameters) and mechanical (rupture limit, conditional yield strength, relative elongation and narrowing upon damaging) characteristics of 09Γ2C steel, which was strengthened using ECAP following different technological regimes, is demonstrated. Therefore, it is possible to estimate the strength and plasticity characteristics of the analyzed material based on the measurement of its magnetic parameters. It has been revealed that under conditions of uniaxial tension in the range from 0 to (0.2–0.6) of the conditional yield strength (depending on the ECAP regime), it is possible to diagnose changes in the stressed state of items that are made of 09Γ2C steel that is hardened in accordance with the ECAP technique using magnetic structuroscopy methods.

A Modification on ECAP Process by Incorporating Twist Channel

In this study, a method that combines the equal channel angular pressing (ECAP) and twist extrusion (TE) techniques has been introduced as a severe plastic deformation process and investigated by means of the three-dimensional finite element analysis. Owing to the form of the mold which is used in this technique, it can be called the symmetrical channels angular pressing (SCAP) method. This method resembles the more common ECAP process for samples with rectangular cross sections, with the difference that, in this method, the entrance and exit channels at the intersecting corner of the mold also have a twist about their longitudinal axis (as in the TE technique). In this study, to show the characteristics of the SCAP method and to compare it with the ECAP technique, the former method has been simulated by the ABAQUS/Explicit software. Also, to validate the obtained results, the SCAP and ECAP methods were practically applied on samples made of pure commercial aluminum (AA1050). To get the strain distribution along the longitudinal and transverse directions of the samples, Vickers hardness was measured on these samples. The results obtained from these hardness measurements indicate that after one pass, the SCAP method can achieve a higher amount of hardness, compared with the ECAP technique. Moreover, the strain distributions obtained from the simulation and from the samples demonstrate that the SCAP method produces a more homogeneous distribution of strain in the workpieces.

The role of the friction during the equal channel angular pressing of an IF-steel billet

It is well known that high levels of friction induce adherence effects in materials processed by equal channel angular pressing (ECAP) promoting some degree of heterogeneity along the deformation zone. In the present paper, the role of the friction in relation of die geometry considering frictionless, ideal lubrication and severe friction conditions of an interstitial free (IF) steel deformed by ECAP technique using plane strain finite element models was investigated in details. The analysis of adherence at the billet–die contact region during only one pass of deformation was carried out in a quasi-static form at room temperature. Independent of the die channels intersection angle (90° or 120°) analyzed an adherence phenomenon was observed under determined friction conditions. It can be concluded that it is necessary to establish an upper limit to the friction coefficient in order to avoid the adherence effect in two-dimensional finite element simulations.

Grain Refinement and Strengthening of a Cylindrical Pure-Aluminum Specimen by Using Modified Equal-Channel Angular Pressing Technique

A new grain refinement and strengthening technique by modified ECAP (equal-channel angular pressing) technique was proposed in this study. ECAP technique is an effective technique for grain refinement and strengthening of metal material. This technique gives high shear plastic strain to the material without geometric transformation of the specimen. However, traditional ECAP technique is restricted by material type and size, especially length. Such kinds of restrictions cause various problems in practical use. We modified traditional ECAP dies and processes to allow high plastic strain for long-length pure-aluminum specimens. Then, grain distribution was observed using a microscope, grain size was determined by the Jeffries and the Heyn methods, and strengthening was investigated by micro-Vickers hardness test. Then the effectiveness of proposed grain refinement or strengthening techniques was discussed.

Fatigue and Tensile Behavior of Cast, Hot-Rolled, and Severely Plastically Deformed AZ31 Magnesium Alloy

The work focuses on experimental examination of the fatigue behavior of magnesium alloy AZ31 produced by three different procedures: squeeze casting (SC), hot rolling (HR), and equal-channel angular pressing (ECAP). The microstructures produced were studied by light and transmission electron microscopy (TEM). Squeeze-cast AZ31 had low porosity and coarse grains, while hot-rolled material showed microstructure with grain size of 3 to 20 μm. The finest grain structure with the average grain size of about 1 to 2 μm was found in the material pressed 4 times at 200 °C using the ECAP technique, route B c . It was shown that low- and high-cycle fatigue behavior under symmetric loading at room temperature and with loading frequency of 20 Hz is strongly dependent on the technique employed in producing the alloy. The ECAP was shown to improve the fatigue life of the material in the low-cycle region over that of the squeeze-cast material. However, the fatigue life of AZ31 after ECAP was slightly lower than that of the hot-rolled material. In the high-cycle region, the hot-rolled material and the material that underwent ECAP exhibit the same fatigue strength, which is superior to that of the squeeze-cast alloy. Fatigue crack initiation and the character of fracture were examined by means of scanning electron microscopy.

Mechanical Properties of Al-5.7wt% Ni Eutectic Alloy Severely Deformed by Equal-Channel Angular Pressing

In this study, an Al-5.7wt% Ni eutectic alloy was subjected to severe plastic deformation (SPD) by an equal-channel angular pressing (ECAP) technique. ECAP technique was carried out by using two strain introduction methods, route BC and route A, at a temperature. It is found that the Al-Ni eutectic alloy specimens after ECAP technique by route BC and route A methods have very different microstructures which affected strongly the tensile properties of the specimens. Namely, after ECAP technique by route BC method, the fine Al3Ni dispersoids of about 300 nm homogeneously dispersed in α-aluminum matrix and the samples appeared no clear anisotropic in tensile properties, while the eutectic textures containing α-Al and Al3Ni fibrous dispersoids have highly anisotropy distribution and are proved to have significant anisotropy tensile properties after ECAP technique by route A method. Results of Young’s modulus and simultaneous internal friction measured by dynamic mechanical analysis (DMA) were also presented. Based on the experimental results, the fracture mechanism during tensile process of the Al-Ni eutectic alloy by different strain induction methods was discussed.

Microstructure and refining performance of an Al-5Ti-0.25C refiner before and after equal-channel angular pressing

Refining experiments were conducted to evaluate the grain refining performance of an Al-5Ti-0.25C refiner before and after equal-channel angular pressing (ECAP) with the use of a high-purity Al. The results show that the Al-5Ti-0.25C refiner has remarkable and stable grain refining performance when the holding times are within 5 to 30 minutes and the melt temperatures are within 1003 to 1073 K. Furthermore, some Al-5Ti-0.25C refiner samples were subjected to severe plastic deformation by using the ECAP technique at 298 K. It was found that Al3Ti and TiC particles were significantly fragmented and their mean sizes were decreased to 10 and 1.08 µm, respectively, and the Al-5Ti-0.25C refiner appeared to have a double grain refining effect in comparison with that of before ECAP. It is also testified that the Vickers microhardness (Hv) value of the pure Al samples refined by the Al-5Ti-0.25C refiner after ECAP processing has a significant increment than that of before ECAP processing. It is concluded that the Al-5Ti-0.25C refiner with ECAP technique has a very useful practical application in refining industrial Al alloys.

Ultrafine-grained Al–5 wt.% Fe alloy processed by ECAP with backpressure

A process for increasing both strength and ductility in a brittle Al–5 wt.% Fe alloy by Equal Channel Angular Pressing (ECAP) was investigated. The increase in solid solubility of iron in the Al matrix produced by intense deformation under ECAP permitted age hardening in this alloy although it is not hardenable by conventional processing. An ultrafine-grained microstructure of 325–450 nm was obtained in a brittle, cast Al–5 wt.% Fe alloy by ECAP with various numbers of passes and backpressure levels from 40 to 275 MPa. A supersaturated solid solution with a maximum solubility of 0.6 wt.% of iron in an aluminium matrix was obtained during ECAP, which allowed ageing of the conventionally non-hardenable alloy. Strength, ductility and microhardness of the cast alloy processed by the ECAP technique were significantly enhanced (e.g. strength and ductility from 102 MPa and 3.4% to 261 MPa and 5.8%, respectively). The subsequent artificial ageing resulted in a further increase in strength to 272 MPa. It was shown by scanning electron microscopy (SEM) that the type of fracture of tensile specimens taken from material subjected to ECAP was predominantly ductile. An increase in backpressure retards cracking of intermetallic particles and enhances the workability and ductility of such alloys processed by ECAP.

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.

ＥＣＡＰ法で製造した微細粒Ａｌ‐３％Ｍｇ‐０．２％Ｓｃ合金の超塑性

This paper describes grain refinement of an Al-3%Mg-0.2%Sc alloy using the equal-channel angular pressing(ECAP) technique at room temperature. It is shown that a grain size of 0.2.MU.m is obtained with this technique. The paper also presents the results of tensile tests for the fine-grained Al-3% Mg-0.2% Sc alloy over a wide range of strain rates. Elongations of more than 1000% are attained at a temperature of 673K in a high strain rate range of more than 10-2s-1. Transmission electron microscopy and scanning ion microscopy are employed for microstructural observations before and after tensile testing. The results are compared with those of a cold-rolled Al-3%Mg-0.2%Sc alloy. It is demonstrated that grain refinement using the ECAP technique is useful for the production of Al alloys exhibiting high strain rate superplasticity.