Influence of grain size on microstructure, mechanical properties and strain hardening behavior of Mg-0.3Ca (wt.%) alloy
Influence of grain size on microstructure, mechanical properties and strain hardening behavior of Mg-0.3Ca (wt.%) alloy
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DOI：
10.1016/j.msea.2022.142847
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发表时间：
2022-02
期刊：
影响因子：
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通讯作者：
X. Liu;X. Qiao;W. Xie;R. Pei;L. Yuan;M. Zheng
中科院分区：
文献类型：
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作者：
X. Liu;X. Qiao;W. Xie;R. Pei;L. Yuan;M. Zheng
Mg-0.3Ca（X 03，重量%）通过低温挤压和随后的退火热处理，获得了不同晶粒尺寸的二元合金。挤压态X 03合金的拉伸屈服强度（TYS）、极限拉伸强度（UTS）和断裂伸长率（EL）分别为361 MPa、370 MPa和10.6%。361 MPa的异常高的TYS主要是由于超细动态再结晶晶粒的强化和Ca原子在晶界的偏聚。位错发射的高能量势垒从晶界钉扎偏析的钙原子增加激活位错成核所需的张应力。退火处理后，随着平均晶粒尺寸从0.7 μm增加到6.0 μm，X 03合金的TYS从361 MPa明显降低到94 MPa，而EL从10.6%增加到29.6%。细晶试样（晶粒尺寸小于2 μm）在拉伸过程中出现异常应变软化现象。应变软化机制可能主要是由于型位错密度降低所致。平均晶粒尺寸大于2 μm的合金获得了更多的位错储存空间，表现出明显的应变硬化，从而获得较高的断裂伸长率。
Mg-0.3Ca (X03, wt.%) binary alloy with different grain sizes were obtained by low-temperature extrusion and subsequent annealing heat treatment. The tensile yield strength (TYS), ultimate tensile strength (UTS) and elongation to failure (EL) of the as-extruded X03 binary alloy with an ultra-fine grain size of 0.7 μm was 361 MPa, 370 MPa and 10.6%, respectively. The exceptional high TYS of 361 MPa was mainly due to the strengthening from ultra-fine dynamic recrystallized grains with segregation of Ca atoms at grain boundaries. The high energy barrier for dislocation emission from grain boundaries pinned by segregated Ca atoms increases the tensile stress required to activate dislocation nucleation. With increasing average grain sizes from 0.7 μm to 6.0 μm after annealing treatment, the TYS of the X03 alloy was decreased obviously from 361 MPa to 94 MPa, while the EL increases from 10.6% to 29.6%. Abnormal strain softening was observed during tensile test of the fine-grained samples with grain size less than 2 μm. The mechanism of strain softening may be mainly caused by the decrease of type dislocations density. The alloy with average grain size larger than 2 μm attains more space to store dislocations, thus shows obvious strain hardening, which contributes to high elongation to failure.