Al-0.74Fe-0.23Cu合金重复连续挤压组织与性能研究

发布时间：2018-04-14 19:37

本文选题：铝合金 + 连续大塑性变形　；参考：《湖南大学》2015年硕士论文

【摘要】：大塑性变形可以使金属或合金获得极细甚至纳米晶组织,从而大幅度提高金属材料的综合性能。本文利用硬度、拉伸试验以及电导率测量等性能检测手段,以及光学显微镜(OM)、电子背散射衍射分析技术(EBSD)、X射线衍射仪(XRD)、扫描电镜(SEM)、透射电子显微(TEM)等微观组织分析手段,对Al-0.74Fe-0.23Cu合金分别在低速(5rpm)和高速(21rpm)重复连续挤压过程中组织与性能的演变规律进行研究,探讨铝合金重复连续挤压实现连续大塑性变形工艺方法的可能性及其效果。主要研究结果如下:1.水平连铸(HCC)Al-0.74Fe-0.23Cu合金横截面、纵截面的组织在晶粒大小、晶粒形貌、晶体取向分布方面不同。在水平连续铸造凝固过程中产生Al Fe,Al Fe Si以及Al Si析出相。2.在低速重复连续挤压过程中,连续挤压可以提高水平连铸合金强度和塑性,但随着挤压道次的增加,合金的强度和硬度逐渐降低而延伸增加,表现出一种明显的加工软化现象。3.在低速重复连续挤压过程中,第一道次连续挤压后,Al-0.74Fe-0.23Cu合金形成明显的挤压纤维组织,表明合金软化机制以回复为主,但在后续的重复连续挤压过程中,发现了应变累积诱发连续动态再结晶的发生。此外,在低速重复连续挤压过程中,第一道次连续挤压可以诱导一些相溶解和诱导Al7Cu2Fe新相的动态析出,并且明显改变原始组织的晶粒取向和共晶相的分布状态。进一步的连续挤压对合金组织的晶粒取向分布影响不大,但随着挤压道次的增加,析出相进一步破碎细化、分布变得越来越均匀。4.与低速重复连续挤压相比,高速重复连续挤压时合金的力学性能演化规律与低速重复连续挤压相似,但高速重复连续挤压明显加速了合金组织和力学性能演化的进程。5.高速重复连续挤压加速了合金中沉淀相的均匀分布行为,但没有加速沉淀相的破碎行为。第一道次连续挤压过程后合金中出现了部分晶粒细化,表明再结晶发生。随着挤压道次的增加,再结晶过程不断加速,因此合金的强度低于低速重复连续挤压的强度。此外,发现在高速重复连续挤压的开始阶段,合金中出现了剪切带,因此可以认为新的细晶粒的产生可能与高速连续挤压时形成的剪切带有关。
[Abstract]:Large plastic deformation can make metal or alloy obtain very fine or even nanocrystalline structure, thus greatly improve the comprehensive properties of metal materials.In this paper, hardness, tensile test and electrical conductivity measurement were used, as well as optical microscope, electron backscatter diffraction analysis technique, X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and so on.The evolution law of microstructure and properties of Al-0.74Fe-0.23Cu alloy during repeated continuous extrusion at low speed (5rpm) and high speed (21rpm) were studied, and the possibility and effect of repeated continuous extrusion of aluminum alloy to realize continuous large plastic deformation were discussed.The main results are as follows: 1.In horizontal continuous casting, the microstructure of HCCU Al-0.74Fe-0.23Cu alloy is different in grain size, grain morphology and crystal orientation distribution.During the solidification process of horizontal continuous casting, Al Fe Fe Si and Al Si precipitated phases. 2.In the process of low speed repeated continuous extrusion, continuous extrusion can improve the strength and plasticity of the horizontal continuous casting alloy, but with the increase of extrusion pass, the strength and hardness of the alloy gradually decrease and increase, showing an obvious softening phenomenon of machining.In the low speed repeated continuous extrusion process, the Al-0.74Fe-0.23Cu alloy formed obvious extrusion fiber structure after the first continuous extrusion, which indicated that the softening mechanism of the alloy was mainly the recovery mechanism, but in the subsequent repeated continuous extrusion process,Continuous dynamic recrystallization induced by strain accumulation was found.In addition, during the low speed repeated continuous extrusion, the first continuous extrusion can induce the dissolution of some phases and induce the dynamic precipitation of the new phase of Al7Cu2Fe, and obviously change the grain orientation of the original microstructure and the distribution of the eutectic phase.The further continuous extrusion had little effect on the grain orientation distribution of the alloy, but with the increase of extrusion pass, the precipitation phase was further broken and refined, and the distribution became more and more uniform.Compared with low speed repeated continuous extrusion, the evolution law of mechanical properties of alloy under high speed repeated continuous extrusion is similar to that of low speed repeated continuous extrusion, but high speed repeated continuous extrusion obviously accelerates the evolution of microstructure and mechanical properties of alloy.High speed repeated continuous extrusion accelerates the uniform distribution of precipitate phase in the alloy, but does not accelerate the fracture behavior of the precipitated phase.After the first continuous extrusion process, some grain refinement occurred in the alloy, indicating that recrystallization occurred.The recrystallization process accelerates with the increase of extrusion pass, so the strength of alloy is lower than that of low speed repeated continuous extrusion.In addition, it is found that in the initial stage of high speed repeated continuous extrusion, shear bands appear in the alloy, so it can be concluded that the production of new fine grains may be related to the shear bands formed during high speed continuous extrusion.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG379;TG146.21

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