Development of Microstructure and Properties of Mg-Y-(Nd)-Zn Alloys during Heat and Mechanical Treatment

• DOI: 10.4028/www.scientific.net/ddf.369.157
• Publication Date: 2016-07-06T06:14:09Z
• Authors: Tomáš Kekule; Hana Kudrnova; Martin Vlach; Bohumil Smola; Ivana Stulíková
• Keywords: 0203 mechanical engineering; 02 engineering and technology

This work is focused on development of microstructure and properties of Mg-Y-Zn and Mg-Y-Nd-Zn alloys during heat and mechanical treatment. In the as-cast state both alloys exhibit almost equiaxed grains with little larger size in Mg-Y-Zn alloy and grain boundaries decorated by different structures - long period ordered structure (LPSO) was detected in Mg-Y-Zn alloy and eutectics of Mg3Nd type structure in alloy with Nd addition. A high density of stacking faults is evident in both alloys. Both alloys were repeatedly isochronally heat treated from room temperature up to 440 °C. Resistivity and microhardness measurement was performed after each heating step. Stacking faults persist both annealings in both alloys and microhardness development shows no remarkable differences. LPSO in Mg-Y-Zn alloy disappears after the first annealing and was again detected after repeated annealing up to 340 °C. After the whole treatment no grain growth appeared. Differential scanning calorimetry measurement was performed at both repeatedly heated alloys up to 540 °C. There are three exothermic peaks in DSC curves of Mg-Y-Zn alloys that can be ascribed to embedding solute atoms in stacking faults, LPSO development and transformation and coarsening of grain boundary particles. DSC curves of Mg-Y-Nd-Zn alloy exhibit two exothermic peaks that probably correspond to precipitation of basal plates of γ ́and γ phase. Measurement of microhardness was performed after sequential deformation of both alloys in the as-cast state. The alloys were cold rolled in steps of 0,9 % thickness reduction up to cracks formation. Strengthening of both alloys is very similar but formation of cracks in the alloy with Nd addition begins after a lower reduction (about 11 %) compared to Mg-Y-Zn alloy (about 15 %).