Microstructures evolution and mechanical properties of dilute Mg-Y-Al-Ca-Mn alloy during uniaxial compression deformation at different strain levels

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The isothermal compression tests of dilute as-extruded Mg-2Y–1Al (wt%) alloy, Mg-2Y–1Al-0.3Ca-0.7Mn (wt%) alloy and Mg-2Y–1Al-0.7Ca-0.3Mn (wt%) alloy were systematically carried out. The experimental temperature (T) was 200 °C, the strain rate (ε̇) was 0.001 s−1 and the strain levels ranged from 0.1 to 0.3. Tests results demonstrated that compressive strength and yield strength clearly increased after adding Ca and Mn, just as Mg-2Y–1Al-0.3Ca-0.7Mn alloy and Mg-2Y–1Al-0.7Ca-0.3Mn alloy had displayed. It was worth mentioning that peak stress of Mg-2Y–1Al-0.7Ca-0.3Mn alloy was 100 MPa higher than that of Mg-2Y–1Al alloy under the strain count of 0.3. The main reason was that adding Ca and Mn into Mg-2Y–1Al caused existence of more second phases which made microstructure finer. Furthermore, microstructures evolution and deformation mechanisms of three alloys were investigated by electron backscatter diffraction (EBSD). Based on EBSD results, what could be found was there existed plenty of twins which could be determined to be {10−12} extension twin when strain count is 0.1. And because of more second phases, Mg-2Y–1Al-0.3Ca-0.7Mn alloy and Mg-2Y–1Al-0.7Ca-0.3Mn alloy activated more extension twins than Mg-2Y–1Al alloy. When strain count was 0.3, it could be seen that three alloys all occurred dynamic recrystallization (DRX) and the main DRX mechanism was strongly believed to be discontinue dynamic recrystallization (DDRX). According to dislocation slip analysis results of three alloys, much pyramidal <c+a> slip and little prismatic <a> slip was activated during compression and dominated deformation.