Influence of grain size on the flow properties of an Al-Mg-Sc alloy over seven orders of magnitude of strain rate

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractExperiments were conducted to evaluate the flow properties of an Al-3Mg-0.2Sc alloy both without and with processing using equal-channel angular pressing (ECAP). The initial grain size was ~300 m and this was reduced to ~250 nm by ECAP and then increased to ~600 nm by annealing at 673 K for 10 min. Tests were conducted to determine the mechanical properties over seven orders of magnitude of strain rate from ~10 -4 to ~10 3 s -1 .The results confirm the validity of the Hall-Petch relationship in the material processed by ECAP. Shear banding occurred in the coarse-grained material during dynamic testing but in the ECAP-processed alloy there was only minor grain coarsening. There was evidence for dynamic strain ageing in both the coarse and the ultrafine-grained (UFG) alloy with a transition in flow mechanism at high temperatures from dislocation climb in the coarsegrained material to superplasticity in the UFG alloy.

Examining the Thermal Stability of an Al-Mg-Sc Alloy Processed by High-Pressure Torsion

“…In addition, both the experimental datum points referring to the Al-3Mg-0.2Sc alloy and the data plotted for the HPT-processed Al-3Mg alloy corresponding to d Figure 5 also reveals an apparent breakdown in the Hall-Petch relationship in the Al-3Mg alloy for d < ~0.25 µm whereas the Hall-Petch relationship remains valid for the Al-3Mg-0.2Sc alloy in the entire range of grain sizes evaluated in this and other studies 22 . The apparent absence of saturation in the hardness values of the Al-3Mg-0.2Sc alloy after 10 turns of HPT as well as the continuing linearity between H and d -1/2 indicate that the UFG metal with Sc additions deforms primarily by intragranular dislocation glide at ambient temperature.…”

“…Therefore, with the aim of improving the thermal stability of Al-Mg alloys, these metals may be alloyed with Sc additions because Al 3 Sc precipitates are effective in pinning the grain boundaries and retaining ultrafine grains even at high temperatures [15][16][17][18] . Several investigations have demonstrated the outstanding mechanical properties and superplastic behaviour of Al-Mg-Sc alloys processed by ECAP [19][20][21][22] . Elongations of > 2000 % 19,20 were attained in the ECAP-processed material tested in tension at T ≥ 673 K at initial strain rates higher than 1.0 × 10 -2 s -1 .…”

“…There have been numerous exploratory studies discussing the validity of the Hall-Petch relationship for Al-Mg and Al-Mg-Sc alloys processed by ECAP and HPT 12,18,22,26,35,36 . In order to verify if this relationship remains accurate for Al-Mg-Sc alloys, the Vickers microhardness is plotted as a function of d -1/2 for the Al-3Mg 12,35 and the Al-3Mg-0.2Sc alloy after HPT processing at ambient temperature and after HPT followed by annealing for 1 h at temperatures ranging from 423 to 773 K, as depicted in Figure 5.…”

“…The apparent absence of saturation in the hardness values of the Al-3Mg-0.2Sc alloy after 10 turns of HPT as well as the continuing linearity between H and d -1/2 indicate that the UFG metal with Sc additions deforms primarily by intragranular dislocation glide at ambient temperature. There is experimental evidence of deformation-induced segregation of Mg at grain boundaries and triple junctions in Al-Mg-Sc alloys during SPD processing 22,26 . Therefore, as these segregations are effective in suppressing the emission of extrinsic dislocations, they permit the action of intragranular slip as the most favourable deformation mechanism in this Al alloy at low homologous temperatures.…”

Peculiar behaviour of pure ENAW-Al99.5 sheet metal during uniaxial tensile test

“…For the purpose of improving its mechanical properties and plasticity Al is often alloyed with Mn and Mg and the materials thereof are used for higher levels of deep drawing. The behaviour of these alloys has been investigated by many authors [1][2][3][4][5][6][7][8][9] in order to determine the technological, mechanical, thermal, electro-chemical, etc. properties.…”