Abstract

This research investigates the microstructural evolution, mechanical properties, and corrosion behavior of AZ91 magnesium alloy after the process of hydrostatic cyclic expansion extrusion (HCEE) at elevated temperature. The HCEE process is able to produce long length ultrafine-grained rods by applying high hydrostatic pressure. The results showed that ultrafine-grained microstructure appears after the consecutive passes of the process, which led to the higher hardness and strength with an increased elongation to failure in the processed rods at room temperature. The ultimate tensile strength and elongation to failure of the processed rod after two cycles of the HCEE increased more than 2 and 2.6 times, respectively. Moreover, an increase in hardness was more than 100% after the second cycle of the process and its distribution was more uniform. Furthermore, the ultrafine-grained microstructure after the HCEE resulted in the movement of potentiodynamic polarization derived curves to higher values of corrosion potential (E_corr) and lower current density (I_corr), which shows the capability of the HCEE process in improving the corrosion resistance of AZ91 magnesium alloy rods. These increases in corrosion resistance were further indicated by the Nyquist diagram derived from the electrochemical impedance spectroscopy scanning and evolved hydrogen amount after 208 h of immersion in 3.5% NaCl solution. The novel HCEE process shows further its capability in producing long length ultrafine-grained rods with superior mechanical and corrosion properties rather than other severe plastic deformation techniques.

Graphic Abstract

中文翻译：

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静液压循环膨胀挤压的严重塑性变形方法对AZ91镁合金的组织，力学和腐蚀性能的影响

摘要

本研究研究了在高温下进行静液压循环膨胀挤压（HCEE）后，AZ91镁合金的组织演变，力学性能和腐蚀行为。HCEE工艺可以通过施加高静水压力来生产长尺寸的超细棒。结果表明，在连续加工之后，会出现超细晶粒的微观结构，从而导致更高的硬度和强度，并在室温下提高了加工棒的断裂伸长率。两次HCEE循环后，加工棒的极限抗拉强度和断裂伸长率分别增加了2倍和2.6倍。而且，在该过程的第二个循环之后，硬度的增加超过100％，并且其分布更加均匀。_更正件）和较低的电流密度（I_更正件），其示出了在改进AZ91镁合金棒的耐腐蚀性HCEE过程的能力。这些耐蚀性的增加由电化学阻抗谱扫描得出的奈奎斯特图进一步表明，在3.5％NaCl溶液中浸泡208小时后释放出的氢量。新颖的HCEE工艺进一步显示了其生产具有优异机械和腐蚀性能的长超细晶粒棒材的能力，而不是其他严格的塑性变形技术。

图形摘要