KEKULE Tomáš Univerzita Karlova v Praze

Spoluautoři STULÍKOVÁ Ivana, SMOLA Bohumil, VLACH Martin, KUDRNOVÁ Hana

Phase transformations and microhardness changes during isochronal annealing were investigated in Mg2Y1Nd1Zn and Mg2Y1Zn alloys prepared by powder metallurgy and extruded at 280 °C. These alloys were annealed in 20 °C/20 min steps from room temperature up to 440 °C. Several experimental methods were performed: electrical resistivity measurements at 77 K and at room temperature, measurement of microhardness, differential scanning calorimetry, optical microscopy and transmission and scanning electron microscopy. Results of measurements were compared to squeeze cast Mg2Y1Nd1Zn and Mg2Y1Zn alloys. Resistivity of the Mg2Y1Zn decreases up to annealing temperature 300 °C, then increases up to 380 °C and is followed by a constant value up to 440 °C. Resistivity annealing curve of Mg2Y1Nd1Zn is little more complicated. These curves in comparison to curves of squeeze cast identically treated alloys are different but exhibit similarities if repeated heating is performed. Microhardness was measured in two different orientations: perpendicular and parallel to direction of extrusion. Microhardness of both alloys in both orientations exhibits an outstanding thermal stability up to 360 °C and exceeds that of squeeze cast alloys about approximately 50 %. No pronounced grain growth was observed even after high temperature annealing at 440 °C where microhardness decreases to almost 75 % of its initial value.