An evaluation of high temperature tensile properties for a magnesium AZ31 alloy processed by high-pressure torsion

Y. Huang, P.H.R. Pereira, R.B. Figueiredo, T. Baudin, A. Helbert, F. Brisset, T.G. Langdon
Accepted: 29 March 2015
Citation: Y. Huang, P.H.R. Pereira, R.B. Figueiredo, T. Baudin, A. Helbert, F. Brisset, T.G. Langdon. An evaluation of high temperature tensile properties for a magnesium AZ31 alloy processed by high-pressure torsion. Letters on Materials, 2015, 5(3) 341-346
BibTex   DOI: 10.22226/2410-3535-2015-3-341-346

Abstract

A magnesium alloy AZ31 was processed by high-pressure torsion (HPT) at room temperature. Microstructure investigations show the material has a grain size as fine as ~450 nm after 5 turns of HPT processing. X-ray texture measurements show most grains have the {0001}<uvtw> fibre, with their c-axis parallel to the HPT torsion axis. Tensile specimens were cut from HPT disc and pulled to failure over a range of strain rates (4.5×10-5, 1.3×10-4, 1.3×10-3 and 1.3×10-2 s-1) at temperatures of 623 and 673 K. The tensile elongations from HPT specimens are lower than for published results using equal-channel angular processing (ECAP) specimens although AZ31 has a finer grain size after HPT than after ECAP. The reasons for the lower elongations in HPT specimens are related to the thermal stability of the processed microstructure, the texture components and the tensile specimen size. Earlier investigations confirmed there was significant grain growth at 623 and 673 K in HPT samples, which would contribute to the low ductility of AZ31 in tensile testing. The main {0001}<uvtw> fibre in HPT samples means in tensile specimens most grains have their basal plane parallel to the surface of the tensile specimen, leading to the low ductility because the critical resolved shear stress does not operate on the basal plane due to the small Schmid factor that is nearly zero. The tensile specimen thickness in HPT is thinner than in ECAP and it is known that the ductility decreases when reducing the specimen thickness.

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