Jacek Skiba

Development of high-strength pure magnesium and wrought magnesium alloys AZ31, AZ61, and AZ91 processed by hydrostatic extrusion with back pressure

Abstract Cold hydrostatic extrusion with and without back pressure of commercial Mg 99.5+% and AZ31, AZ61, and AZ91 wrought magnesium alloys has been performed on a press operating up to 2000 MPa with a back pressure reaching up to 700 MPa. Application of back pressure extended the formability of Mg, and AZ-type magnesium alloys, which decreases with the increase in the Al content. Fibrous and elongated grains above 1 micrometre and nanometre scale sub-grains and grains were observed. The strength of all materials was significantly higher in comparison to materials conventionally and hydrostatically hot-extruded, hot ECAP-ed or after hot wire drawing. In comparison to materials processed by traditional methods the ultimate tensile strength increment after hydrostatic extrusion with back pressure increases gradually with an increase in Al content reaching for AZ91 almost 40%. The potential application of AZ-type magnesium alloys as semi-products for degradable medical implants or high strength structural components is indicated.

Influence of Severe Plastic Deformation Induced by HE and ECAP on the Thermo-Physical Properties of Metals

The study is aimed at comparing the changes which occur in the microstructure and thermo-physical properties of pure copper (99.9%) and when copper alloyed with chromium and zirconium subjected to severe plastic deformation (SPD). The plastic deformation techniques employed were hydrostatic extrusion (HE), equal channel angular pressing (ECAP), and a combination of these two processes. The materials thus obtained had an ultra-fine-grained structure with the thermo-physical properties differing from those of the untreated materials. It appeared that there is a correlation between the deformation method employed and the thermo-physical properties of the materials, such as diffusivity and specific heat.

Processing of Copper by Equal Channel Angular Pressing (ECAP) – Microstructure Investigations

The present study attempts to apply Equal-Channel Angular Pressing (ECAP) to 99.99% pure copper. ECAP process was realized at room temperature for 4, 8 and 16 passes through route BC using a die having angle of 90°. The microstructure of the samples was investigated by means both light and transmission electron microscopy. Additionally the microhardness was measured and statistical analysis of the grains and subgrains was performed. Based on Kikuchi diffraction patterns misorientation was determined. There were some different types of bands in the microstructure after deformation. The shear bands, bands and in the submicron range the microshear bands and microbands are a characteristic feature of the microstructure of copper. Also characteristic was increasing of the number of bands with increasing of deformation and mutually crossing of the bands. The intersection of a bands and microbands leads to the formation of new grains with the large misorientation angle. The measured grain/subgrain size show, that the grain size is maintained at a similar level after each stage of deformation and is equal to d = 0.25 – 0.32 μm.