Takayoshi Fujinami

The potential for scaling ECAP: effect of sample size on grain refinement and mechanical properties

Abstract The potential for scaling equal-channel angular pressing (ECAP) for use with large samples was investigated by conducting tests on an aluminum alloy using cylinders having diameters from 6–40 mm. The results show the refinement of the microstructure and the subsequent mechanical properties after pressing are independent of the initial size of the sample and, for the largest sample with a diameter of 40 mm, independent of the location within the sample at least to a distance of ∼5 mm from the sample edge. By making direct measurements of the imposed load during ECAP, it is shown that the applied load is determined by the sample strength rather than frictional effects between the sample and the die walls. The results demonstrate the feasibility of scaling ECAP to large sizes for use in industrial applications.

Improvement of mechanical properties for Al alloys using equal-channel angular pressing

Abstract Equal-channel angular pressing (ECAP) was attempted at room temperature to refine grain sizes of six different commercial Al alloys, 1100, 2024, 3004, 5083, 6061 and 7075. Transmission electron microscopy revealed that submicrometer grain sizes are attained in these alloys. Tensile tests at room temperature showed that the strength increases with an increase in the number of pressings but the elongation to failure remains little changed following a large decrease after the first pressing. Static annealing experiments demonstrated that the extensive grain growth occurs above ∼200°C in 1100, 3004, 5083 and 6061 but the submicrometer-grained structures are stable in 2024 and 7075 even at 300°C. It was confirmed that the Hall–Petch relationship holds for the ECA-pressed alloys. The effect of sample size was further examined and the applied load was measured during ECAP for the possibility of scaling-up the process.

Influence of rolling on the superplastic behavior of an Al-Mg-Sc alloy after ECAP

It is now well established that the grain size of metallic alloys may be substantially refined, to the submicrometer or even the nanometer range, through the application of severe plastic deformation [1–3]. Several experimental techniques are available for applying the deformation but Equal-Channel Angular Pressing (ECAP) is an especially attractive procedure because it provides an opportunity for producing reasonably large fully-dense bulk samples. It was noted earlier [4] that, since the strain rate associated with optimum superplasticity is displaced to faster strain rates when the grain size is reduced, it may be possible to use ECAP to prepare materials capable of exhibiting superplastic ductilities at rapid strain rates above ; 10 s in the region generally designated High Strain Rate Superplasticity [5]. Several reports have confirmed this possibility in both commercial and laboratory alloys [6–10]. The introduction of a rapid forming capability through ECAP was also demonstrated recently in an Al-3% Mg-0.2% Sc alloy by cutting disks from the as-pressed rods and forming into domes using a simple biaxial gas-pressure forming facility [11]. It follows from these preliminary results that it may be feasible to use ECAP to overcome the limitations imposed on conventional superplastic forming operations due to the relatively slow forming rates ( ;10–10 s) and the long forming times (;20–30 minutes) required for the production of each component [12,13]. Samples produced by ECAP are generally in the form of rods with either square or circular cross-sections. Although this shape is suitable for use in superplastic forging operations, it is not appropriate for conventional superplastic forming where materials are in the form of thin sheets. To date, there are no results showing whether the superplastic characteristics introduced into a material by ECAP, and revealed in standard tensile testing, are also retained if the as-pressed materials are subsequently rolled into sheets. The present investigation was initiated to evaluate the effect of cold rolling after ECAP. The Al-3% Mg-0.2% Sc alloy was selected for use in these experiments because it was established earlier that this alloy exhibits exceptionally high tensile ductilities at rapid strain rates following ECAP [11].

Application of analytical electron microscopy to diffusivity measurement requiring X-ray absorption correction

Abstract X-ray microanalysis using an analytical electron microscope is applied to diffusivity measurements in an alloy system where the X-ray absorption correction is imperative. It is shown that the differential X-ray absorption (DXA) method is useful for the absorption correction in the determination of a concentration gradient across a diffusion couple interface.

Influence of Channel Geometry on Superplasticity in Equal-Channel Angular Pressing

Equal-channel angular pressing (ECAP) was conducted on an Al-1%Mg-0.2%Sc alloy using a die having a channel angle ( ) of 90 o but with two different angles, 0 o and 90 o , for the outer arc of curvature ( ). Microstructures were observed by optical microscopy and transmission electron microscopy to examine the effect of . Tensile tests were also conducted and the ductility was examined for the ECAP samples processed with the two different angles, =0 o and =90 o . It is shown that the microstructure was more homogeneous for =0 o than =90 o . However, larger ductility was obtained for the samples processed with =90 o than =0 o .