Influence of Production and Heat Treatment on Microhardness and Phase Transformations in Mg-Y-(Nd)-Zn Alloys
Abstract
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.
Electrical resistivity measurements at 77 K, measurement of microhardness, optical microscopy and transmission and scanning electron microscopy were used. Results were compared to squeeze cast Mg2Y1Nd1Zn and Mg2Y1Zn alloys.
Resistivity annealing curves of alloys prepared by powder metallurgy exhibit similarities to those of squeeze cast alloys already one time isochronally heat treated. Microhardness was measured in two different orientations: perpendicular and parallel to extrusion direction.
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.