Hydrostatic twist extrusion (HTE) for processing relatively long ultrafine grained samples

Abstract

In this study, hydrostatic twist extrusion (HTE) has been introduced for processing relatively long ultrafine grained (UFG) bulk samples. By using high-pressure fluid surrounded the sample, surface contact between die and sample was eliminated. The high-pressure fluid causes high hydrostatic pressure, which leads to improvement of material properties and increased the aspect ratio of the sample (length/diameter). The HTE process was applied to commercial pure aluminum samples at room temperature, and then microstructure and mechanical properties were examined. The results demonstrate that after HTE process, the grain size was reduced from 54 µm to ∼800 nm, and microhardness was increased from 29.2 HV to 37.7 HV. Also, yield and ultimate strength were noticeably increased from 78 MPa and 103 MPa to 166 MPa and 175 MPa, respectively. This process seems to be very promising and interesting for the future industrial application.