Study on the plasticity improvement mechanism and grain refinement of AZ80 Mg alloy under cryogenic multi-directional forging

IF 6.2 2区 材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY Journal of Materials Research and Technology-Jmr&t Pub Date : 2024-09-13 DOI:10.1016/j.jmrt.2024.09.096
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Abstract

The introduction of twin lamellae and dislocation interaction through Multi-directional forging (MDF) at room temperature (RT) has been reported to significantly improve the mechanical properties of Mg alloys. However, the Mg alloys typically exhibited poor plasticity at RT, making it highly susceptible to cracking. This study further enhanced the deformation capacity of AZ80 Mg alloy by adding a pre-cryogenic step before MDF. Compared to direct MDF at RT, MDF at cryogenic temperature (CT, −196 °C) further increased the alloy's deformation capacity from 0.72 (4P) to 1.08 (6P), with the tensile yield strength (TYS) and ultimate tensile strength (UTS) increasing to ∼420 MPa and ∼512 MPa. The alloy subjected to cryogenic MDF exhibited denser twin lamellae and a higher proportion of {10–12}-{10–12} twin interactions. The more frequent twin interactions under CT inhibited excessive twin growth and further increased the dislocation density of the matrix, facilitating the nucleation of new twins. Additionally, with increasing deformation passes, the texture of the RT specimens became more single, while the CT specimen showed a trend toward texture dispersion. The study elucidated that poor forgeability of the alloy under MDF at RT was hindered by unfavorable texture and limited twin activation. However, this issue was mitigated under CT, where the activation of more atypical twins with low Schmid factors (SFs) significantly enhanced the deformation coordination ability. Furthermore, the activation of atypical twins and extensive twin interactions promoted texture dispersion in CT specimens, which facilitated the activation of various slips/twins and suppressed excessive twinning-induced hardening, thereby improving forgeability.

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低温多向锻造条件下 AZ80 镁合金塑性改善机理及晶粒细化研究
据报道,在室温(RT)下通过多向锻造(MDF)引入孪生薄片和位错相互作用可显著改善镁合金的机械性能。然而,镁合金在室温下通常塑性较差,极易开裂。本研究通过在中密度纤维前添加预冷冻步骤,进一步提高了 AZ80 镁合金的变形能力。与直接在室温下进行中密度纤维化相比,在低温(CT,-196 °C)下进行中密度纤维化进一步提高了合金的变形能力,从 0.72 (4P) 提高到 1.08 (6P),拉伸屈服强度 (TYS) 和极限拉伸强度 (UTS) 分别提高到 ∼ 420 MPa 和 ∼ 512 MPa。经过低温中密度纤维化处理的合金表现出更致密的孪晶薄片和更高比例的{10-12}-{10-12}孪晶相互作用。在 CT 条件下,更频繁的孪晶相互作用抑制了孪晶的过度生长,并进一步提高了基体的位错密度,促进了新孪晶的成核。此外,随着变形次数的增加,RT 试样的纹理变得更加单一,而 CT 试样则呈现出纹理分散的趋势。该研究阐明,RT 条件下的 MDF 合金锻造性较差是由于不利的纹理和有限的孪晶活化造成的。然而,这一问题在 CT 条件下得到了缓解,低施密特因子(SF)的非典型孪晶的激活显著增强了变形协调能力。此外,非典型孪晶的激活和广泛的孪晶相互作用促进了 CT 试样中纹理的分散,这有利于各种滑移/孪晶的激活,并抑制了孪晶引起的过度硬化,从而提高了锻造性。
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来源期刊
Journal of Materials Research and Technology-Jmr&t
Journal of Materials Research and Technology-Jmr&t Materials Science-Metals and Alloys
CiteScore
8.80
自引率
9.40%
发文量
1877
审稿时长
35 days
期刊介绍: The Journal of Materials Research and Technology is a publication of ABM - Brazilian Metallurgical, Materials and Mining Association - and publishes four issues per year also with a free version online (www.jmrt.com.br). The journal provides an international medium for the publication of theoretical and experimental studies related to Metallurgy, Materials and Minerals research and technology. Appropriate submissions to the Journal of Materials Research and Technology should include scientific and/or engineering factors which affect processes and products in the Metallurgy, Materials and Mining areas.
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