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Abstract
An Al-3%Mg-0.2%Sc alloy was processed by ECAP and HPT at different temperatures. Afterwards, samples subjected to 10 turns of HPT at 300 and 450 K, 8 passes of ECAP at 300 K and 10 passes of ECAP at 600 K were annealed for 1 hour at 523 K and their mechanical properties and microstructure were examined using microhardness measurements and EBSD analysis. In addition, tensile specimens with similar dimensions were machined from the HPT and ECAP-processed materials and further tensile tested at 523 K. The results demonstrate that the Al alloy processed by HPT at 450 K exhibits higher microhardness values (~138 Hv) and a smaller average grain size (~0.28 µm) after annealing at 523 K among all SPD processing conditions. Accordingly, the material subjected to HPT at an elevated temperature displays superior superplastic properties such that an elongation of ~1020 % was attained after testing at 523 K at 1.0 × 10−3 s−1. Furthermore, detailed EBSD analysis revealed a significant fraction of low-angle grain boundaries (LAGBs > 33 %) in the ECAP-processed material after annealing which may be responsible for the inferior superplastic behaviour by comparison with the HPT-processed samples (LAGBs < 13 %) tested at 523 K.
Highlights
There is a growing interest in the application of Al alloys in the transportation industry for replacing heavier structural components usually fabricated with steel and reduce the energy consumption and, thereby the pollutant emissions from motor vehicles [1]
Detailed electron backscattered diffraction (EBSD) analysis revealed a significant fraction of low-angle grain boundaries (LAGBs > 33 %) in the equalchannel angular pressing (ECAP)-processed material after annealing which may be responsible for the inferior superplastic behaviour by comparison with the high-pressure torsion (HPT)-processed samples (LAGBs < 13 %) tested at 523 K
It is clearly noted from these plots that the microhardness distribution along the diameter of discs is fairly uniform after post-severe plastic deformation (SPD) annealing, except for the metal processed by ECAP at 300 K which displays higher hardness values at the centre of the sample
Summary
There is a growing interest in the application of Al alloys in the transportation industry for replacing heavier structural components usually fabricated with steel and reduce the energy consumption and, thereby the pollutant emissions from motor vehicles [1]. In order to satisfy this demand, processing by severe plastic deformation (SPD) [2,3], as in high-pressure torsion (HPT) [4] and equalchannel angular pressing (ECAP) [5], has been successfully used to produce ultrafine-grained (UFG) metals having remarkably enhanced properties by comparison with materials subjected to conventional thermo-mechanical processing. There are numerous studies showing the outstanding superplastic properties of Al-Mg-Sc alloys processed by ECAP [8,9,14,15]. The Al-3Mg-0.2Sc alloy subjected to 8 passes of ECAP at room temperature achieves an elongation of ~2580 % after tensile testing at 723 K at 3.3 × 10-3 s-1 [8]
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