UFG and nanocrystalline microstructures produced by hydrostatic extrusion of multifilament wires

Abstract

Abstract Aluminium, Al-4Cu-0.5Mg-1Mn aluminium alloy (AA2017), copper, iron and nickel in the form of a bundle of wires placed in appropriate capsules were subjected to cumulative hydrostatic extrusion to form 3 mm wires with total true strain above 10 in Al, the aluminium alloy and Cu and above 7 in Ni and Fe. The deformation was first induced in single wires which were then assembled and further deformed to form a multifilament wire. The final product had a nanocrystalline (grain size below 100 nm in Fe and the 2017 Al alloy) and ultra-fine grain (below 130 nm in Ni and below 270 nm in Cu and Al) microstructure. The grain refinement resulted in the microhardness being increased, with the greatest increase to 3.5 GPa being achieved in iron. During hydrostatic extrusion, the severe deformation was possible due to the high applied pressures of up to 1.7 GPa. The hydrostatic extrusion of multifilament wires broadens the application range of this process extending it to the fabrication of ultra-fine grain and nanocrystalline microstructures.