Abstrakt
Phase transformations during isochronal annealing were investigated in squeeze cast Mg2Y1Zn and Mg2Y1Nd1Zn alloys. Electrical resistivity measurements at 77 K and room temperature, differential scanning calorimetry and microhardness measurements were performed.
Transmission electron microscopy and optical microscopy revealed intermetallic phases at grain boundaries and in their vicinity and a relatively high density of stacking faults in grain interiors of both alloys. Resistivity annealing curves show matrix enrichment by solutes in both alloys during isochronal annealing up to 440 oC.
Only a weak precipitation proceeds during isochronal annealing of both alloys. Mechanical properties tested by microhardness measurements do not deteriorate due to the isochronal annealing.
If a repeated isochronal annealing of both alloys previously isochronally annealed up to 440 oC is performed, an early precipitation stage appears in both alloys at 80 oC - 200 oC. Thermal stability of microhardness remains very good also in the repeated heat treatment.
Heat flow connected to the phase transformations up to 440 oC is only moderate, but a partial liquefaction was observed near to 500 oC in calorimetrical curves. The melting temperature shifts to lower temperatures in repeated isochronal annealing only in the Mg2Y1Zn alloy.