Materials Science Forum Vols. 503-504

Abstract: Twist Extrusion (TE) is a process of severe plastic deformation (SPD) being developed by us during recent 5 years. Upon this time we published few papers on mechanics of the process and influence of the TE processing on materials structure and properties. Here we reported some results on application of the twist extrusion processing and made few general conclusions.

Abstract: The paper describes hydrostatic extrusion (HE) as a method of grain refinement of metallic materials down to the nanometric scale. The main features of this method are: (a) large strain, (b) very high strain rates (even greater than 104 s-1), and (c) deformation homogeneity. HE offers also the opportunity of obtaining bulk materials in a variety of forms (rods and wires of complex cross-sections, small tubes). The study undertaken on 4 materials (aluminium, aluminium alloy, copper and titanium) has shown that significant grain refinement , down to nanometric scale in the case of titanium and aluminium alloy, occurred during HE processing. This grain refinement produces significantly improved mechanical properties. It has been found that HE offers good prospects for the production of nano-structured metals and alloys.

Abstract: Six years have passed since the international workshop “Investigations and Applications of Severe Plastic Deformation” held 2-8 August 1999 in Moscow, Russia. This workshop focused on severe plastic deformation (SPD) processing to produce bulk nanostructured metals and alloys. Since 1999 the field has expanded from 200 to over 2000 publications that have addressed the microstructures and properties that can be produced by a growing number of SPD techniques. In view of this expansion, the outlook for ongoing development of severely deformed materials is updated. Special attention is given to factors influencing the manufacturing and commercialization of SPD-processed metals, including barriers to their widespread application. Recommendations are made for future SPD research that will facilitate more rapid commercialization of SPD-processed metals and enhance the competitiveness of SPD processing with respect to alternative technologies for producing bulk nanostructured metals.

Abstract: Severe plastic deformation (SPD) in solid metals, with an aim to obtaining ultra-fine grained or even nano-structured materials, attracted great efforts all over the world. This article retrospects to the ancient origin of this technique and presents some aspects of recent research activities in China briefly. SPD appeared as “folding and forging” for the fabrication of high quality steel sword as early as ~ BC500, this technique developed and maturated at around AD220~280, with a special term in Chinese “BAI-LIAN” (means Multitudinous Repetitive Processing), the steel fabricated by this process is called BAI-LIAN steel. Inlay gold characters on unearthed ancient steel swords recorded the number of processing repetitions. This ancient technique even resulted in several Chinese idioms very popular until at present time. Current research activities on SPD in China, supported by the National Science Foundation, National high tech program, local government technical programs and enterprises etc., are blooming all over China, in Universities, Chinese Academy of Science, National Research Institute and Enterprises. SPD is becoming a hotspot in materials field in China. Chinese materials scientists expect greatly increasing contribution to the development of SPD.

Abstract: Over the past two decades equal channel angular processing (ECAP) and other severe plastic deformation (SPD) processes have been shown, in the laboratory scale, to produce material with promising properties for industrial applications. In particular, ultrafine grain (UFG) metals produced by ECAP process, for example, have been shown to exhibit higher strain rate sensitivity at lower temperatures and higher strain rates. These factors translate to improved hot formability. However, scale up of these processes to manufacture industrial size components has not been widely undertaken. In this study, billets of annealed AA6061 with 12.5 mm (0.5-in), 50 mm (2-in) and 100 mm (4-in) square cross section were ECAP processed. For the first time, these larger SPD billets were used as starting stock for subsequent hot forging. Several parts were forged on an industrial scale press with the UFG material, as well as conventional stock materials. These parts varied in complexity, as well as size in order to cover the variability in industrial components. This paper will present the effect of scaling up on the mechanical properties, microstructure, and the hot workability of the alloy from the laboratory scale (12.5 mm) to industrial scale (100 mm). Results show that both the forging temperature of the billets and the starting billet size can be substantially decreased compared to conventional forging practice. Therefore, the use of SPD materials, as forging stock, results in decreased energy usage and increased material yield. Results presented will include examples of forged parts, estimated energy savings associated with the use of SPDUFG stock, and properties after forging and subsequent heat treatment.

Abstract: The deformation field associated with chip formation in plane strain (2-D) machining has been simulated using the finite element method (FEM), with the objective of developing 2-D machining as an experimental technique for studying very large strain deformation phenomena. The principal machining parameters are the tool rake angle, cutting velocity and the friction at the toolchip interface while the deformation field parameters are strain, strain rate and temperature. The relation between rake angle and the shear strain in the deformation zone is studied for the low-speed cutting of lead. This correspondence is validated by comparison with measurements of the deformation parameters made by applying a Particle Image Velocimetry (PIV) technique to highspeed photographic image sequences of the deformation. It is shown that plastic strains in the range of 1-15 can be realized in a controlled manner by appropriate choice of the rake angle. The unique capabilities offered by 2-D machining for studying micro- and nano- mechanics of large strain deformation, and the creation of ultra-fine grained materials are highlighted in the context of these results.

Abstract: This study presents a new rapid continuous process for grain refinement in metallic materials through severe plastic deformation (SPD). The new process, designated in this study the severe torsion straining process (STSP), is applicable to a wide range of alloys based on aluminum, magnesium and copper including carbon steel. This process consists of producing a local heated zone in a rod and cooling both sides of the heated zone by spray water while rotating one end with the other. Thus, torsion strain is introduced in the local heated zone. The STSP can be continuous because the straining is achieved while the rod is shifted along the longitudinal axis of the rod. Furthermore, the process requires no die, suggesting a potential for commercialization of grain refinement through SPD. In this study, STSP was applied to an Al-Mg alloy and a Mg-Al-Zn alloy. It is shown that STSP is effective for both alloys so that the grain size is reduced to ~1.5 μm for the Al alloy and ~0.9 μm for the Mg alloy. Tensile testing showed that the strength is increased with a minimal decrease in uniform elongation. There is a critical ratio between rotation speed and moving speed, which defines the feasibility of STSP operation without breaking the rod. The grain size tends to be lowered as the ratio is close to the critical value.

Abstract: High pressure torsion (HPT) is a well-known procedure to impart severe plastic deformation (SPD) into metallic materials. It was reported that HPT produces grain sizes finer than those using other SPD processes such as equal-channel angular pressing (ECAP). However, the application of HPT has been restricted to thin disk samples. In this study, an HPT process was developed for use with bulk samples. This process is designated as Bulk-HPT for comparison with conventional Disk-HPT. Cylindrical samples of an Al-3%Mg-0.2%Sc alloy having dimensions of 10 mm in diameter and 8.6 mm in height were prepared for Bulk-HPT. The samples were strained under a pressure of 1 GPa for 2 turns at room temperature. Microstructural observations revealed that the samples contained regions having a grain size of ~130 nm. Tensile testing showed a superplastic ductility ~480 % at 673 K with an initial strain rate of 3.3x10-2 s-1.

Abstract: The effect of the supersaturated solid solution decomposition occurring prior to, during, and after severe plastic deformation by torsion under high hydrostatic pressure on strengthening is examined by the examples of Al-Cu-Mg, Al-Mg-Sc, and Mg-Sm alloys and 0.12%C-0.85%Mn- 0.65%Si and 0,1%C-1.12%Mn-0.08%V-0.07%Ti low-carbon steels. The decomposition of the supersaturated solid solution was realized upon cooling from the quenching temperature (lowcarbon steels), prior to deformation (Al-Cu-Mg-, Mg-Sm alloys), during deformation (Al-Cu-Mg-, Mg-Sm alloys), and after deformation. It is shown, the decomposition of the supersaturated solid solution is effective for the grain refinement down to nanoscale and strengthening, but, for different materials, different combinations with SPD should be used.