Structural impact on the Hall–Petch relationship in an Al–5Mg alloy processed by high-pressure torsion

Abstract

The evolution of microstructure and microhardness was studied in a commercial 5483Al-5Mg alloy processed by high pressure torsion (HPT) under a pressure of 6.0 GPa up to 10 turns. Significant grain size refinement was observed even after 1/4 turn and additional processing led to a further grain size reduction and a shift in the distribution of grain boundary misorientation angles towards higher values.An essentially fully homogeneous microstructure was reached after 10 turns with a final grain size of ~70 nm, a saturation Vickers microhardness of Hv  240 which was attained at and above equivalent strains of ~150, a relatively narrow grain size distribution and a fraction of ~80% of high-angle grain boundaries. Analysis shows the Hall-Petch plot deviates from the conventional linear relationship for samples processed through small numbers of turns but after 3 or more turns there is a direct correlation between the results obtained in HPT processing and coarsegrained samples.

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

“…9 infers that the Hall-Petch relationship remains accurate for Al-Mg-Sc alloys over the full range of grain sizes evaluated in this and other studies. This is consistent with earlier results on an Al-5Mg alloy processed by HPT for 10 turns to give a grain size of ~70 nm [94].…”

Significance of grain refinement on microstructure and mechanical properties of an Al-3% Mg alloy processed by high-pressure torsion

“…However, the earlier results demonstrated a possible decrease in slope at grain sizes in the range of ~0.09-0.15 µm after processing by HPT where there was a decrease to K H ≈ 10.0 Hv µm -1/2 [19]. As shown in recent investigations of dilute Al-Mg alloys processed by HPT [22,25], the present Al-Mg alloy exhibits excellent Hall-Petch strengthening through grain reduction.…”

“…Recent reports recorded that an Al-1% Mg alloy processed through HPT under 6.0 GPa after >3 turns demonstrated a hardness homogeneity with Hv ≈ 110 [21] and an Al-5% Mg alloy showed a homogeneous distribution of hardness with Hv ≈ 240 after HPT at 6.0 GPa for 10 turns [22]. These results, when considered together with the present hardness experiments, demonstrate that higher Mg contents lead to higher hardness values in homogeneity through HPT and this trend continues up to at least 10% of Mg in the Al matrix after 10 HPT turns [23].…”

Texture and Microtexture of Pure (6N) and Commercially Pure Aluminum after Deformation by Extrusion with Forward-Backward Rotating Die (Kobo)

“…Methods of severe plastic deformation (SPD) such as equal channel angular pressing ECAP [3,4] high pressure torsion HPT [5,6] or accumulative roll bonding ARB [7] are widely used in order to obtain improvement in mechanical properties by grain refinement [1,2] according to Hall-Petch strengthening mechanism. Advantage of these methods is maintaining unchanged initial shape and size.…”