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Ruiqing Lu, Long Zhang, Shuwei Zheng, Dingfa Fu, Jie Teng, Jianchun Chen, Guodong Zhao, Fulin Jiang, and Hui Zhang, Microstructure, mechanical properties and deformation mechanisms of an Al–Mg alloy processed by the cyclical continuous expanded extrusion and drawing approach, Int. J. Miner. Metall. Mater., 29(2022), No. 1, pp.108-118. https://dx.doi.org/10.1007/s12613-021-2342-y
Ruiqing Lu, Long Zhang, Shuwei Zheng, Dingfa Fu, Jie Teng, Jianchun Chen, Guodong Zhao, Fulin Jiang, and Hui Zhang, Microstructure, mechanical properties and deformation mechanisms of an Al–Mg alloy processed by the cyclical continuous expanded extrusion and drawing approach, Int. J. Miner. Metall. Mater., 29(2022), No. 1, pp.108-118. https://dx.doi.org/10.1007/s12613-021-2342-y
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新型循环连续扩展挤压和拉拔工艺对Al–Mg合金的显微组织、力学性能和变形机制研究

摘要: Al–Mg 系铝合金具有较高的机械强度以及优良的可加工性、可焊接性等优点,广泛应用于船舶、军工和航空航天等领域。然而如何进一步提升Al–Mg合金综合力学性能,拓展其应用范围,成为材料科学工作者与工程技术人员追求的目标。大塑性变形(SPD)作为一种能够有效细化金属晶粒进而大幅提升金属材料力学性能的方法获得了越来越多的关注。本文系统研究了一种新型循环连续扩展挤压与拉拔大塑性变形工艺对Al–Mg合金显微组织、力学性能及变形机理的影响。首先通过新型循环连续扩展挤压与拉拔工艺(CCEED)成功制备出3道次挤压和拉拔Al–Mg合金杆料。然后系统介绍了加工样品随着道次增加显微组织及力学性能的演变规律,并结合晶粒尺寸演变模型成功预测了Al–Mg合金晶粒尺寸随加工温度的变化趋势,为指导实际工业生产奠定理论基础。研究结果表明,连续挤压作为一种连续塑性变形加工工艺,能够高效生产超长尺寸金属型材。晶粒细化能够大幅提升Al–Mg合金综合力学性能;冷变形加工(拉拔)能够引入大量位错亚结构,能够进一步细化晶粒尺寸提升力学性能。随着加工道次的增加,由于多道次交叉剪切变形机制,加工样品硬度分布的均匀性逐渐提高。连续扩展挤压主要提高了合金塑性,而冷拔则提高了合金的强度。由于快速的动态恢复速度,加工样品产生了强度饱和现象。循环连续扩展挤压与拉拔循环连续扩展挤压与拉拔处理后,通过连续动态再结晶逐渐细化Al–Mg合金棒材的晶粒尺寸。在挤压试样中,获得了具有许多细亚晶粒的等轴晶粒。对于冷拔试样,观察到具有大量胞状结构和位错的细长晶粒。循环连续扩展挤压与拉拔过程中的微观结构演变基本上受特殊热机械变形条件的影响。 冷拔引入了大量位错并促进了连续动态再结晶以获得细晶。连续动态再结晶在较高温度(500°C)挤压过程中,晶界迁移率(M)显着增加,导致晶粒的快速生长并限制了Al–Mg合金的晶粒细化。最后,本文对未来连续挤压工艺研究工作进行了展望。在连续挤压转速较高的变形条件下,Al–Mg合金晶粒细化的程度有限。在不改变原有Al–Mg合金成分的前提下,即不添加Sc、Zr等微量元素,需尝试降低连续挤压转速,增加连续挤压的冷却系统或冷却频次,并对现有连续挤压槽封块、进料块及其接触长度(包角大小)进行工模具优化设计从而使连续挤压塑性变形区和直接挤压变形区内温度控制在400°C以内。同时较小的扩展尺寸,变形腔内无法获得足够的附加剪切应变,这也限制了晶粒尺寸进一步细化。

 

Microstructure, mechanical properties and deformation mechanisms of an Al–Mg alloy processed by the cyclical continuous expanded extrusion and drawing approach

Abstract: Al–Mg alloys are an important class of non-heat treatable alloys in which Mg solute and grain size play essential role in their mechanical properties and plastic deformation behaviors. In this work, a cyclical continuous expanded extrusion and drawing (CCEED) process was proposed and implemented on an Al–3Mg alloy to introduce large plastic deformation. The results showed that the continuous expanded extrusion mainly improved the ductility, while the cold drawing enhanced the strength of the alloy. With the increased processing CCEED passes, the multi-pass cross shear deformation mechanism progressively improved the homogeneity of the hardness distributions and refined grain size. Continuous dynamic recrystallization played an important role in the grain refinement of the processed Al–3Mg alloy rods. Besides, the microstructural evolution was basically influenced by the special thermomechanical deformation conditions during the CCEED process.

 

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