Strain-controlled cyclic deformation behavior of a high-strength low-alloy (HSLA) Mg-1.2Zn-0.1Ca alloy fabricated via low-temperature extrusion at 150 °C was investigated at different strain amplitudes. Due to the partial dynamic recrystallization (DRX) during extrusion, the extruded HSLA magnesium alloy consisted of a unique heterostructure containing coarse unDRX grains and ultra-fine DRX grains of 0.8 µm, leading to a high tensile yield strength of 374 MPa and an elongation of 14%. The HSLA magnesium alloy exhibited cyclic stabilization at strain amplitudes of ≤0.4%, while cyclic hardening occurred at strain amplitudes of ≥0.6%. In contrast, the homogenized alloy with a uniform coarse-grained microstructure showed a strong cyclic hardening characteristic. Compared with the homogenized alloy, the HSLA magnesium alloy had a significantly higher cyclic stress level at all strain amplitudes, along with a longer fatigue life at lower and intermediate strain amplitudes owing to its higher monotonic strength. However, the homogenized alloy showed a longer fatigue life at a high strain amplitude of 0.8 % due to its better ductility and stronger capacity of storing deformation. While {10–12}<10−11> extension twinning occurred in both the homogenized and HSLA samples at high strain amplitudes, twins were primarily formed in the coarse unDRX grains in the compressive phase during cyclic deformation due to the -axes of unDRX grains perpendicular to the loading direction, with twinning in the ultra-fine DRX grains being suppressed. The low-cycle fatigue life of both the homogenized and HSLA samples can be well predicted through an accumulative damage model based on the strain-energy density calculation and intrinsic fatigue toughness concept.

中文翻译：

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异质结构高强度低合金（HSLA）镁合金的循环变形行为

研究了通过 150 °C 低温挤压制造的高强度低合金 (HSLA) Mg-1.2Zn-0.1Ca 合金在不同应变幅值下的应变控制循环变形行为。由于挤压过程中的部分动态再结晶 (DRX)，挤压 HSLA 镁合金由独特的异质结构组成，其中含有粗大的 unDRX 晶粒和 0.8 µm 的超细 DRX 晶粒，从而具有 374 MPa 的高拉伸屈服强度和14%。HSLA镁合金在应变幅≤0.4%时表现出循环稳定性，而在应变幅≥0.6%时发生循环硬化。相比之下，具有均匀粗晶微观结构的均质合金表现出很强的循环硬化特征。与均质化合金相比，HSLA 镁合金在所有应变幅值下均具有显着更高的循环应力水平，并且由于其较高的单调强度，在较低和中等应变幅值下具有较长的疲劳寿命。然而，均质合金由于其更好的延展性和更强的存储变形能力，在0.8%的高应变幅下表现出更长的疲劳寿命。虽然在高应变幅下均质化样品和 HSLA 样品中都发生了 {10–12}<10−11> 延伸孪晶，但由于 unDRX 晶粒的 - 轴，孪晶主要在循环变形期间的压缩相中在粗 unDRX 晶粒中形成垂直于加载方向，超细 DRX 晶粒中的孪晶受到抑制。通过基于应变能量密度计算和固有疲劳韧性概念的累积损伤模型，可以很好地预测均质样品和 HSLA 样品的低周疲劳寿命。