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Subject: search.filters.subject.Ultrafine grains

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    Effects of strain rate during multi-directional forging on grain refinement and mechanical properties of AZ80Mg alloy
    (2016-01-01)
    Miura, H.
    ;
    Kobayashi, M.
    ;
    Benjanarasuth, T.
    Samples of AZ80Mg alloy were multi-directionally forged (MDFed) at various strain rates in the rage from 3.0× 10-3 s-1 to 3.0× 10-1 s-1 under decreasing temperature conditions. The MDFing pass temperatures employed were 653 K, 605 K and 553 K. These passes, each of 0.5 strain, were applied up to a cumulative strain of ΣΔϵ= 1.5 at maximum. The average grain size decreased with increasing cumulative strain and depended only weakly on the strain rate. Microstructures with average grain sizes of 0.84 μm, 0.88 μm and 1.2 μm were attained when MDFed at strain rates of 3.0× 10-1 s-1, 3.0× 10-2 s-1 and 3.0×10-3 s-1. The microstructure evolved at 3.0× 10-1 s-1 was less homogeneous. This difference is interpreted as being due to the higher stored energy causing static recrystallization in the latter MDFing condition. As a result, the best balance of the mechanical properties was attained by MDFing at 3.0× 10-2 s-1. In this case, ultimate tensile strength (UTS) of 445 MPa was achieved together with a fracture strain of 22%. By comparison, MDFing at 3.0× 10-1 s-1 led to lower UTS and ductility of 410 MPa and 15% while the yield stresses were comparable.
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    An examination of the saturation microstructures achieved in ultrafine-grained metals processed by high-pressure torsion
    (2014-10-01)
    Sabbaghianrad, Shima
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Kawasaki, Megumi
    ;
    Langdon, Terence G.
    Experiments were conducted on two commercial alloys, a Cu-0.1%Zr alloy and an Al-7075 aluminum alloy, to investigate the significance of the saturation microstructure which is achieved after processing by high-pressure torsion (HPT). Samples were processed by HPT and also by a combination of equal-channel angular pressing (ECAP) followed by HPT. The results show that the saturation conditions are dependent upon the grain size in the material immediately prior to the HPT processing. Additional grain refinement may be achieved in HPT by initially processing the material to produce an ultrafine-grain size before conducting the processing by HPT.