Precipitate free zone (PFZ) consistently forms near the grain boundaries (GBs) in precipitate-strengthened alloys, significantly weakening the materials because of their intrinsic softness compared to the bulk. However, the influence of PFZ near GBs on deformation mechanism remains largely unrevealed. Here, we systematically investigate the effects of PFZ on the macroscopic mechanical behavior and the microstructure deformation mechanism of the modelled precipitate-strengthened Al-Zn-Mg-Cu alloy, using a combination approach of experiments, molecular dynamics (MD) simulations, and theoretical modeling. Four Al-Zn-Mg-Cu alloys with highly different PFZ widths are prepared by tailoring the quenching media and applying the new deformation heat- treatment process proposed by us. Experimental characterizations demonstrate that severe dislocation accumulation occurs at the interface between PFZ and bulk. Meanwhile, MD simulations further reveal that PFZ is prone to plastic deformation during tensile process, contributing to the softening of materials. The PFZ exhibits significant strain concentration, leading to the preferential formation of dislocations within PFZ rather than at GBs. It is found that the level of strain concentration and the degree of dislocation accumulation are not sensitive to the PFZ width. Based on these mechanisms, a PFZ-dependent strength model is developed to quantitatively evaluate the influence of PFZ on tensile strength by considering dynamic strengthening of PFZ. It is predicted that an increase in PFZ width greatly reduces the tensile strength, with a 21 % reduction observed when PFZ width reaches 268 nm, emphasizing the important impact of PFZ width on materials strength.

中文翻译：

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探讨无沉淀区沉淀强化合金的微观机制：实验和理论研究


无沉淀区 (PFZ) 在沉淀强化合金的晶界 (GB) 附近始终形成，由于其固有的柔软性（与块体相比），显着削弱了材料的强度。然而，GBs附近的PFZ对变形机制的影响仍然很大程度上未被揭示。在这里，我们采用实验、分子动力学 (MD) 模拟和理论相结合的方法，系统地研究了 PFZ 对模拟沉淀强化 Al-Zn-Mg-Cu 合金的宏观力学行为和微观结构变形机制的影响。造型。通过调整淬火介质并应用我们提出的新形变热处理工艺，制备了四种具有高度不同 PFZ 宽度的 Al-Zn-Mg-Cu 合金。实验表征表明，PFZ 和块体之间的界面处发生严重的位错积累。同时，MD模拟进一步表明PFZ在拉伸过程中容易发生塑性变形，导致材料软化。 PFZ 表现出显着的应变集中，导致位错在 PFZ 内优先形成，而不是在 GB 处形成。结果发现，应变集中的水平和位错积累的程度对PFZ宽度不敏感。基于这些机制，建立了PFZ相关强度模型，通过考虑PFZ的动态强化来定量评估PFZ对拉伸强度的影响。据预测，PFZ 宽度的增加会大大降低拉伸强度，当 PFZ 宽度达到 268 nm 时，拉伸强度会降低 21%，这强调了 PFZ 宽度对材料强度的重要影响。