Effects of solute segregation at grain boundaries (GBs) on the deformation mechanism and fracture behavior remain obscure for magnesium (Mg) alloys. Here, by introducing Zn segregation at GBs, we obtained an Mg-0.5Al-0.4Mn-0.2Ce-0.4Zn (wt.%) alloy achieving fracture elongation (FEL) of ∼33.6 %, with a remarkable FEL improvement by 100 % in comparison to Zn-free counterpart. Meanwhile, the tensile yield strength (TYS, 195.5 MPa) is increased by ∼27.5 MPa after trace Zn addition. Although trace Zn addition improves the fraction of GBs with high misorientation, it reconciles crack tolerance with enhanced strength. The introduction of Zn not only promotes pyramidal 〈 + 〉 slips and inhibits twinning nucleation, but also enhances the GB cohesion by Zn segregation. Based on microstructure observation, we found that the enhanced GB cohesion enables the segregation-inspired hierarchical crack buffering, as well as deflecting and branching. Enhanced GBs can also facilitate the continuous emission of 〈 + 〉 dislocations in neighboring grains irrespective of the onset of microcracks, forming a plastic zone to retard local strain concentration, thus avoiding microcrack percolation and attaining a crack-mediated elongation reserve of above 15 %. Besides, the higher TYS in the Zn-containing alloy mainly stems from the enhanced solid-solution strengthening of Zn solutes, thus achieving strength and crack tolerance synergy.

中文翻译：

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稀镁合金中溶质偏析介导的晶界内聚力增强，裂纹容忍度和强度得到改善

对于镁（Mg）合金来说，晶界（GB）处的溶质偏析对变形机制和断裂行为的影响仍然不清楚。在这里，通过在晶界处引入 Zn 偏析，我们获得了 Mg-0.5Al-0.4Mn-0.2Ce-0.4Zn (wt.%) 合金，其断裂伸长率 (FEL) 约为 33.6 %，FEL 显着提高了 100 %与无锌对应物相比。同时，添加微量Zn后，拉伸屈服强度（TYS，195.5 MPa）增加了~27.5 MPa。虽然微量锌的添加提高了高取向差的晶界的比例，但它协调了裂纹耐受性和增强的强度。 Zn的引入不仅促进金字塔<+>滑移、抑制孪生成核，而且通过Zn偏析增强GB内聚力。基于微观结构观察，我们发现增强的晶界内聚力能够实现受偏析启发的分层裂纹缓冲，以及偏转和分支。增强的晶界还可以促进相邻晶粒中〈+〉位错的连续发射，而不管微裂纹是否出现，形成塑性区以延缓局部应变集中，从而避免微裂纹渗透并获得超过15%的裂纹介导伸长储备。此外，含锌合金较高的TYS主要源于Zn固溶强化的增强，从而实现强度和裂纹容限的协同作用。