目的 探明锻造次数对Mg-Gd-Y-Zn-Zr镁合金硬度及微观组织的影响规律,揭示孪晶及位错演化的机理。方法 首先对挤压态Mg-Gd-Y-Zn-Zr镁合金进行均匀化处理,然后在室温下进行不同变形道次（每道次单向压缩变形量为7.5%）的多向锻造实验;利用维氏硬度计分析不同变形道次对试样硬度的影响;利用OM光学显微镜和SU5000扫描电镜分析试样微观组织变化。结果 通过对试样硬度进行分析,可以发现,随着变形道次的增加,试样硬度可达100HV,较未变形试样提高了33%。通过对试样微观组织进行分析可以发现,试样在变形过程中主要产生$\{10 \overline{1} 2\} $拉伸孪晶,孪晶的相互作用促使晶粒破碎细化;织构强度呈现出先降低后升高的非单调变化趋势;几何必须位错（GND）密度不断增加,与硬度变化呈正相关。同时,试样在多向锻造过程中由于大量滑移系被激活开动,小角度晶界显著增加。此外,根据拉伸孪晶的变化规律提出3种特征孪晶演化模型,包括孪晶界的收缩与膨胀、合并与相交。结论 在室温下对Mg-Gd-Y-Zn-Zr镁合金进行多向锻造实验,可有效利用孪生行为对Mg-Gd-Y-Zn-Zr镁合金进行组织调控,改善其力学性能。
Abstract
The work aims to clarify the effect of forging passes on the hardness and microstructure of Mg-Gd-Y-Zn-Zr magnesium alloy and reveal the underlying mechanisms of twin and dislocation evolution. The as-extruded Mg-Gd-Y-Zn-Zr alloy was firstly treated through homogenization, followed by multi-directional forging at room temperature with different numbers of deformation passes (each pass involved uniaxial compression with a deformation amount of 7.5%). The effect of different deformation passes on sample hardness was analyzed with a Vickers hardness tester. Optical microscopy (OM) and SU5000 scanning electron microscopy (SEM) were employed to examine the microstructural evolution. Hardness analysis revealed that as the cumulative strain increased, the hardness of the sample reached up to 100HV, representing a 33% improvement compared to the undeformed sample. Microstructural observations indicated that $\{10 \overline{1} 2\} $ tensile twins were predominantly formed during deformation, and their interactions promoted grain fragmentation and refinement. The texture strength exhibited a non-monotonic trend, initially decreasing and then increasing. The density of geometrically necessary dislocations (GND) continuously increased, showing a positive correlation with the hardness evolution. Additionally, due to the activation of numerous slip systems during multi-directional forging, the fraction of low-angle grain boundaries significantly increased. Based on the characteristics of tensile twin evolution, three representative twin evolution models were proposed: contraction, expansion, merging and intersection of twin boundaries. This study demonstrates that room temperature multi-directional forging of Mg-Gd-Y-Zn-Zr alloy can effectively utilize twinning behavior to regulate its microstructure and improve mechanical properties.
关键词
Mg-Gd-Y-Zn-Zr镁合金 /
室温 /
多向锻造 /
硬度 /
孪生行为 /
位错密度
Key words
Mg-Gd-Y-Zn-Zr magnesium alloy /
room temperature /
multi-directional forging /
hardness /
twin behavior /
dislocation density
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基金
山西省青年科学基金（202203021212145）
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