AZ80镁合金在室温多向锻压过程中所形成的高密度超细孪晶可显著提升合金的力学性能，但其对合金力学各向异性的影响仍有待研究。本工作基于微观组织表征、力学性能测试和失效分析等方法，本工作研究了室温多向锻压技术对轧制态AZ80镁合金中高密度超细孪晶的形成及力学各向异性的影响规律。微观组织观察结果表明，轧制态样品RD (轧向)-TD (横向)、ND (法向)-TD和ND-RD取向表面测得的平均晶粒尺寸分别为15.7、16.2和18.5 μm。室温下经在单道次6%应变条件下多向锻压6道次后，基体晶粒内形成了大量高密度超细孪晶，合金样品RD-TD、ND-TD和ND-RD取向表面上测得的平均晶粒尺寸分别减小至3.1、2.8和3.5 μm。同时，高密度超细孪晶的形成不仅弱化了合金的基面织构强度，还可使晶粒的c轴向RD的偏转角度大于TD。力学性能测试结果表明，高密度超细孪晶的形成可显著提升轧制态合金样品的力学性能，但表现出明显的力学各向异性。其中，轧制态合金样品沿RD的屈服强度、抗拉强度和延伸率分别为132 MPa、303 MPa和15.4%，沿TD分别为138 MPa、302 MPa和14.5%。经多向锻压后，合金样品沿RD的屈服强度、抗拉强度和延伸率分别为259 MPa、357 MPa和8.8%，沿TD则分别为361 MPa、459 MPa和6.4%。失效分析结果表明，轧制态合金样品沿RD和TD拉伸时，微裂纹主要萌生于孪晶界，多向锻压态合金样品的微裂纹主要萌生于晶界。

Magnesium alloys, as low-cost commercial metallic materials with light weight, low density, good castability, and dimensional stability, are widely used in lightweight industries such as transportation and aerospace. However, the traditional hot deformation process limits the performance enhancement of magnesium alloys, significantly restricting their industrial applications. Through a novel multidirectional forging (MDF) process, tensile twins can be introduced to the maximum extent, effectively refining the grain structure and markedly improving mechanical strength. However, the twin structure may alter the texture, further affecting mechanical anisotropy. In this work, microstructural characterization, tensile testing, and failure analysis were conducted to investigate the effects of high-density ultrafine twins, formed via the MDF technique, on the mechanical anisotropy of as-rolled AZ80 Mg alloy. Microstructural observation shows that the average grain sizes of the rolling direction–transverse direction (RD–TD), normal direction (ND)–TD, and ND–RD surfaces for the as-rolled sample are 15.7, 16.2, and 18.5 μm, respectively. After six passes of MDF under a single-pass strain of 6% at room temperature (25 ℃), high-density ultrafine twins were formed within the grains, and the average grain sizes of the RD–TD, ND–TD, and ND–RD surfaces of the MDF-processed sample were reduced to 3.1, 2.8, and 3.5 μm, respectively. The formation of high-density ultrafine twins not only weakens the basal texture intensity but also causes the c-axis of grains to deflect by a larger angle with respect to RD than to TD. Tensile testing demonstrates that the introduction of such twins significantly improves mechanical properties but induces pronounced mechanical anisotropy. For the as-rolled samples, the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) along RD are 132, 303 MPa, and 15.4%, respectively, whereas along TD they are 138, 302 MPa, and 14.5%. After MDF, the YS, UTS, and EL along RD are 259, 357 MPa, and 8.8%, while along TD they are 361, 459 MPa, and 6.4%, respectively. Failure analysis indicates that, in the as-rolled samples tested along RD and TD, microcracks preferentially initiate at twin boundaries, whereas in MDF-processed samples, microcracks mainly occur at grain boundaries.