Low-temperature superplastic behavior of a submicrometer-grained 5083 Al alloy fabricated by severe plastic deformation

Abstract

A submicrometer-grained structure was introduced in a commercial 5083 Al alloy by imposing an effective strain of ϳ8 through equal channel angular pressing. In order to examine the low-temperature superplastic behavior, the as-equal channel angular pressed (as-ECAP) samples were tensile tested in the strain rate range of 10 Ϫ5 to 10 Ϫ2 s Ϫ1 at temperatures of 498 to 548 K corresponding to 0.58 to 0.65 T m , where T m is the incipient melting point. The mechanical data of the alloy at 498 and 548 K exhibited a sigmoidal behavior in a double logarithmic plot of the maximum true stress vs true strain rate. The strain rate sensitivity was 0.1 to 0.2 in the low-and high-strain rate regions and 0.4 in the intermediate-strain rate region, indicating the potential for superplasticity. At 523 K, instead of the sigmoidal behavior, a strain rate sensitivity of 0.4 was maintained to low strain rates. A maximum elongation of 315 pct was obtained at 548 K and 5 ϫ 10 Ϫ4 s Ϫ1 . The activation energy for deformation in the intermediate-strain rate region was estimated as 63 kJ/mol. Low-temperature superplasticity of the ultrafine grained 5083 Al alloy was attributed to grain boundary sliding that is rate-controlled by grain boundary diffusion, with a low activation energy associated with nonequilibrium grain boundaries. Cavity stringers parallel to the tensile axis were developed during deformation, and the failure occurred in a quasi-brittle manner with moderately diffusive necking.

An Investigation of Cavity Development during Superplastic Flow in a Zinc–Aluminum Alloy Processed Using Severe Plastic Deformation

“…The consistent feature of cavity stringers formed along the tensile axis was reported in unpressed Zn22% Al alloy 28,29,31,34,45,46) and in some superplastic Al alloys processed by ECAP. 17,47,48) It is known that these cavity stringers are directly affected by the presence of impurities, oxide particles and precipitates which are broken and aligned in the stress direction during thermo-mechanical processing operations such as rolling. 49) Third, as with the quantitative cavity measurements, there is a transition in the cavity size and shape with increasing elongation.…”

Grain refinement and superplasticity in a magnesium alloy processed by equal-channel angular pressing

“…For example, there are numerous reports of high strength and high superplastic elongations in various aluminum alloys after processing by ECAP. [11][12][13][14] By contrast, only limited success has been reported when the ECAP procedure is used with hcp metals. An early attempt to achieve significant grain refinement in pure Mg with a grain size of ϳ400 m was unsuccessful, and it was reported instead that the as-pressed grain size was Ͼ100 m after pressing for two passes to a strain of ϳ2 at 673 K. [15] Similarly, a relatively large grain size of ϳ17 m was produced in an Mg-0.9 pct Al solid solution alloy having an initial grain size of ϳ100 m after pressing through two passes at 473 K, [15] where this and all subsequent compositions are given in weight percent.…”

Comparison of compressive deformation of ultrafine-grained 5083 Al alloy at 77 and 298 K

“…The ECAP of eight passes (an effective strain of ϳ8) with route B c was also carried out at 473 K on the annealed sample; the detailed ECAP procedures are described elsewhere. [6,7] The equal channel angular pressed alloy was fully annealed at 453 K for 48 hours; hereafter, it is called the UFG alloy. The preliminary test showed that 453 K was ϳ30 K below the recrystallization temperature of the present UFG alloy.…”