汽车用高性能铝合金强化析出相的演变及调控
发布时间：2018-09-03 10:33
【摘要】：在原子尺度揭示硬化析出相结构和成分的变化是理解和调控复杂多相合金微观结构的关键,对开发高性能合金材料非常重要。本论文以各种先进的电子显微学方法和性能测试为手段,结合计算分析,以重要的汽车用时效强化铝合金为研究对象,系统研究了铝合金中硬化纳米析出相的结构演变及其与性能之间的关系,主要结论如下:1.利用电子显微学方法研究Al-Si合金时效过程Si颗粒界面处的析出情况,以及Al-Si-Mg合金Si颗粒球化处理对时效过程硬化相析出的影响。退火过程中共晶硅颗粒上可以析出连续多重{111}[112]型纳米孪晶,其有时具有相当复杂的结构,比如三重和四重孪晶,以及多晶材料不多见的封闭五重孪晶。延长A356合金的球化处理时间对后续人工时效硬度响应有不利影响,其本质原因是Mg元素偏聚降低了基体中用于形成强化相的Mg含量。2.结合定量高分辨率电子显微学、环形暗场扫描透射电子显微学和计算分析建立了Al-Mg-Si-(Cu)合金中不同析出相在原子尺度的结构演变物理冶金图像。本文的发现对揭示Mg/Si含量比和Cu含量对Al-Mg-Si-Cu合金显微结构和力学性能的影响非常重要,通过适当的时效工艺控制析出方式可以优化合金性能。另外,本文提供的演变规律可以作为理解添加多余元素(如Ag和过渡金属)的Al-Mg-Si合金析出机制的基础。3.添加Cu会显著提升Al-Mg-Si合金的早期时效硬化潜力和速率,即使Mg/Si比是2的Al-Mg-Si-Cu合金的时效动力学也很快。通过优化合金成分配比,本文提出了一种新的用于制备汽车车身用Al-Mg-Si-Cu合金板材的成分范围(Mg/Si含量比1~2),既提高了铝合金板材的加工成形性和烤漆后的强度,又保证了其使用过程中性能的稳定。4.结合形变和时效,提出一种调控铝合金时效过程中纳米析出相的新策略。通过控制轧制前合金元素的聚集和分布状态以及后续时效工艺,可以使铝合金强度显著上升但塑性保持不变。通过控制冷轧前的化学状态,比如合金元素的聚集和分布,可以调控后续时效过程的析出,相对于T6峰值时效的Al-Mg-Si-Cu合金,改进的工艺可以使塑性保持不变而强度提升30%。经后续时效后,自然时效预处理的样品中存在两类析出相:离散分布的板条状Q"类型析出相以及尺寸更大且连续弯曲的析出相,后者成分接近Q'类型析出相。冷轧前短时间人工时效诱导的纳米尺度共格颗粒(单斜β"相的GP区)能够促使均匀细密Q"类型析出相在后续时效过程的形成。本文提出的方案可以应用到很多析出硬化的合金系统中,形变和时效结合的工艺极大地改变了制备合金的腐蚀特性,合金不但具有优良的力学性能,其抗腐蚀性同时也得到了明显改善。通过合理设计后续时效工艺,可以使硬度提高的同时导电率显著提高。5.利用显微硬度测试、拉伸测试、热分析和透射电镜观察研究了后续时效工艺对冷轧Al-Mg-Si-Cu合金微观结构演变和力学性能的影响,揭示了变形合金时效时溶质原子扩散和缺陷退化交互作用的物理图像。析出相和晶粒结构的转变具有温度依赖性,三类溶质原子偏聚过程会发生,包括位错亚胞界面偏聚、基体析出和晶界偏聚。随时效温度提高,时效动力学明显加快。在70℃和120℃后续时效可以使合金硬度持续上升直到一个平台,时效温度高于150℃后,合金到达峰值后会发生明显软化。透射电镜观察和DSC分析揭示,冷轧合金时效析出特性与传统T6时效过程显著不同。70℃时效时溶质原子参与了位错释放和重组的过程并形成了位错胞晶面偏聚物,可以使强度和塑性同时升高,120℃以上时效时基体中析出大量板条相。调控同时发生的基体析出和位错胞界面偏聚可以优化冷轧Al-Mg-Si-Cu合金强度和塑性的结合。当时效温度高于150℃时界析出会发生,强度和塑性明显降低。在180℃时效后期晶界析出相(Q相和S相)几乎耗尽了所有溶质原子,晶粒内部没有位错胞偏聚物和板条状析出相,这可能是溶质原子扩散受再结晶中晶界运动影响的结果。6.析出硬化的Al-Mg-Si-Cu合金在六个不同状态下轧制:四个不同时间的自然预时效(合金内部形成不同的溶质团簇),欠人工时效处理和峰值人工时效处理,然后进行后续时效处理。峰值人工时效预处理降低了合金的轧制性能,引起了肉眼可见的边缘开裂。后续时效过程的溶质再析出随变形前溶质状态变化很大,溶质原子再析出可以补偿强度损失并减轻晶体缺陷(位错和晶界)对塑性的负面影响。相对于T6处理,自然时效和欠人工时效预处理的样品经后续时效后强度可以提升20-40%,峰值人工时效预处理的样品强度可以提升40-50%,但塑性很小,欠人工时效预处理的样品获得了最优的强度和塑性结合。轧制前的预时效对后续时效过程的析出反应有很大影响,自然时效预处理的样品后续时效时析出反应类型相似,其差别是每个析出反应过程形成析出相的总量,峰值人工时效预处理的样品后续时效不会发生明显的析出反应。后续时效后自然时效预处理的样品中形成两类析出相:离散的板条状Q"相和位于位错胞界面长且弯曲的析出相。人工时效预处理样品中的析出相经轧制后位于局部区域并在后续时效时重新变得有序,轧制前欠人工时效预处理样品中的早期β"相经后续时效转变成细小且均匀分布的板条状Q"相。峰值时效预处理的样品中轧制前含有单斜的β"相,轧制后析出相仍存在,但有序性显著损失,经后续时效,铝基体处于高应变状态且Q'类型的析出相仍被大量位错包围。
[Abstract]:Revealing the changes of the structure and composition of hardened precipitates at the atomic scale is the key to understand and control the microstructure of complex multiphase alloys and is very important to develop high performance alloy materials. The main conclusions are as follows: 1. The precipitation at the interface of Si particles during aging of Al-Si alloy and the effect of spheroidizing treatment of Si particles on the precipitation of hardened phase during aging of Al-Si-Mg alloy were studied by means of electron microscopy. Continuous multiple {111} [112] type nanotwins can be precipitated on eutectic silicon particles during annealing, sometimes with rather complex structures, such as triple and quadruple twins, and closed quintuple twins, which are rare in polycrystalline materials. It is the segregation of Mg that reduces the content of Mg used to form the strengthening phase in the matrix. 2. Combined with quantitative high resolution electron microscopy, ring dark field scanning transmission electron microscopy and computational analysis, physical metallurgical images of the structural evolution of different precipitated phases in Al-Mg-Si-(Cu) alloys at atomic scale have been established. The effect of Cu content on the microstructure and mechanical properties of Al-Mg-Si-Cu alloy is very important. Proper aging process can optimize the properties of Al-Mg-Si-Cu alloy by controlling precipitation. In addition, the evolution law provided in this paper can be used as a basis for understanding the precipitation mechanism of Al-Mg-Si alloy with superfluous elements (such as Ag and transition metals). In order to improve the early aging hardening potential and rate of Al-Mg-Si alloy, even if the Mg/Si ratio is 2, the aging kinetics of Al-Mg-Si-Cu alloy is very fast. By optimizing the alloy composition ratio, a new composition range (Mg/Si ratio 1~2) for preparing Al-Mg-Si-Cu alloy sheets for automotive body is proposed. Combining deformation and aging, a new strategy is proposed to control the nano-precipitates in the aging process of aluminum alloy. By controlling the aggregation and distribution of alloy elements before rolling and the subsequent aging process, the strength of aluminum alloy can be significantly increased, but the strength of aluminum alloy can be improved. By controlling the chemical state before cold rolling, such as the aggregation and distribution of alloy elements, the precipitation of subsequent aging process can be controlled. Compared with T6 peak aging Al-Mg-Si-Cu alloy, the improved process can keep the plasticity unchanged and increase the strength by 30%. Precipitate-like phase: Discretely distributed strip-like Q "type precipitates and larger and continuously curved Q" type precipitates whose composition is close to that of Q'-type precipitates. Nano-scale coherent particles (GP region of monoclinic beta phase) induced by artificial aging before cold rolling can promote the formation of uniform and fine Q "type precipitates" in the subsequent aging process. The proposed scheme can be applied to many precipitation hardening alloys. The combination of deformation and aging process has greatly changed the corrosion characteristics of the alloys. The alloys not only have excellent mechanical properties, but also their corrosion resistance has been significantly improved. The effect of subsequent aging on microstructure evolution and mechanical properties of cold rolled Al-Mg-Si-Cu alloy was investigated by means of microhardness test, tensile test, thermal analysis and transmission electron microscopy. The physical image of interaction between solute atom diffusion and defect degradation during aging was revealed. The structure transformation is temperature dependent, and the segregation of three solute atoms occurs, including dislocation subcellular interface segregation, matrix precipitation and grain boundary segregation. The aging kinetics is obviously accelerated with the increase of aging temperature. The results of transmission electron microscopy and DSC analysis show that the precipitation characteristics of cold rolled alloys are significantly different from those of traditional T6 aging process. The solute atoms participate in the process of dislocation release and recombination and form dislocation cell surface segregates, which can increase the strength and plasticity at the same time and aging above 120 C. The strength and plasticity of cold rolled Al-Mg-Si-Cu alloy can be optimized by controlling matrix precipitation and interfacial segregation of dislocation cells. The strength and plasticity of cold rolled Al-Mg-Si-Cu alloy decrease significantly when the aging temperature is higher than 150 C. The precipitates at grain boundaries (Q phase and S phase) are almost exhausted at the later stage of aging at 180 C. Dislocation cell segregates and strip-like precipitates are absent in solute atoms, which may be the result of solute atom diffusion affected by grain boundary movement in recrystallization. 6. Precipitated and hardened Al-Mg-Si-Cu alloys are rolled in six different states: four natural pre-aging at different time (different solute clusters are formed in the alloy), under artificial time. The rolling properties of the alloy were reduced and the visible edge cracking was caused by the peak aging pretreatment. The solute re-precipitation during the subsequent aging process changed greatly with the solute state before deformation. The solute atom re-precipitation could compensate the strength loss and reduce the crystal defect. Compared with T6 treatment, the strength of samples treated by natural aging and under-artificial aging can be increased by 20-40% after subsequent aging, and the strength of samples treated by peak artificial aging can be increased by 40-50%, but the plasticity is very small. The samples pretreated by less artificial aging have the best strength and plasticity. Pre-aging before rolling has a great influence on the precipitation reaction of the subsequent aging process. The precipitation reaction types of the samples after natural aging pretreatment are similar. The difference is the total amount of precipitation phases formed in each precipitation reaction process. The precipitation reaction of the samples after peak artificial aging pretreatment is not obvious. Two types of precipitates are formed in the samples pretreated by natural aging after aging: the discrete strip Q "phase and the long and curved precipitates at the interface of dislocation cells. After subsequent aging, the precipitates in the samples pretreated by peak aging contain monoclinic beta phase before rolling, but there is a significant loss of order. After subsequent aging, the aluminum matrix is in a high strain state and the Q'type precipitates are still surrounded by a large number of dislocations.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.21
本文编号：2219725
[Abstract]:Revealing the changes of the structure and composition of hardened precipitates at the atomic scale is the key to understand and control the microstructure of complex multiphase alloys and is very important to develop high performance alloy materials. The main conclusions are as follows: 1. The precipitation at the interface of Si particles during aging of Al-Si alloy and the effect of spheroidizing treatment of Si particles on the precipitation of hardened phase during aging of Al-Si-Mg alloy were studied by means of electron microscopy. Continuous multiple {111} [112] type nanotwins can be precipitated on eutectic silicon particles during annealing, sometimes with rather complex structures, such as triple and quadruple twins, and closed quintuple twins, which are rare in polycrystalline materials. It is the segregation of Mg that reduces the content of Mg used to form the strengthening phase in the matrix. 2. Combined with quantitative high resolution electron microscopy, ring dark field scanning transmission electron microscopy and computational analysis, physical metallurgical images of the structural evolution of different precipitated phases in Al-Mg-Si-(Cu) alloys at atomic scale have been established. The effect of Cu content on the microstructure and mechanical properties of Al-Mg-Si-Cu alloy is very important. Proper aging process can optimize the properties of Al-Mg-Si-Cu alloy by controlling precipitation. In addition, the evolution law provided in this paper can be used as a basis for understanding the precipitation mechanism of Al-Mg-Si alloy with superfluous elements (such as Ag and transition metals). In order to improve the early aging hardening potential and rate of Al-Mg-Si alloy, even if the Mg/Si ratio is 2, the aging kinetics of Al-Mg-Si-Cu alloy is very fast. By optimizing the alloy composition ratio, a new composition range (Mg/Si ratio 1~2) for preparing Al-Mg-Si-Cu alloy sheets for automotive body is proposed. Combining deformation and aging, a new strategy is proposed to control the nano-precipitates in the aging process of aluminum alloy. By controlling the aggregation and distribution of alloy elements before rolling and the subsequent aging process, the strength of aluminum alloy can be significantly increased, but the strength of aluminum alloy can be improved. By controlling the chemical state before cold rolling, such as the aggregation and distribution of alloy elements, the precipitation of subsequent aging process can be controlled. Compared with T6 peak aging Al-Mg-Si-Cu alloy, the improved process can keep the plasticity unchanged and increase the strength by 30%. Precipitate-like phase: Discretely distributed strip-like Q "type precipitates and larger and continuously curved Q" type precipitates whose composition is close to that of Q'-type precipitates. Nano-scale coherent particles (GP region of monoclinic beta phase) induced by artificial aging before cold rolling can promote the formation of uniform and fine Q "type precipitates" in the subsequent aging process. The proposed scheme can be applied to many precipitation hardening alloys. The combination of deformation and aging process has greatly changed the corrosion characteristics of the alloys. The alloys not only have excellent mechanical properties, but also their corrosion resistance has been significantly improved. The effect of subsequent aging on microstructure evolution and mechanical properties of cold rolled Al-Mg-Si-Cu alloy was investigated by means of microhardness test, tensile test, thermal analysis and transmission electron microscopy. The physical image of interaction between solute atom diffusion and defect degradation during aging was revealed. The structure transformation is temperature dependent, and the segregation of three solute atoms occurs, including dislocation subcellular interface segregation, matrix precipitation and grain boundary segregation. The aging kinetics is obviously accelerated with the increase of aging temperature. The results of transmission electron microscopy and DSC analysis show that the precipitation characteristics of cold rolled alloys are significantly different from those of traditional T6 aging process. The solute atoms participate in the process of dislocation release and recombination and form dislocation cell surface segregates, which can increase the strength and plasticity at the same time and aging above 120 C. The strength and plasticity of cold rolled Al-Mg-Si-Cu alloy can be optimized by controlling matrix precipitation and interfacial segregation of dislocation cells. The strength and plasticity of cold rolled Al-Mg-Si-Cu alloy decrease significantly when the aging temperature is higher than 150 C. The precipitates at grain boundaries (Q phase and S phase) are almost exhausted at the later stage of aging at 180 C. Dislocation cell segregates and strip-like precipitates are absent in solute atoms, which may be the result of solute atom diffusion affected by grain boundary movement in recrystallization. 6. Precipitated and hardened Al-Mg-Si-Cu alloys are rolled in six different states: four natural pre-aging at different time (different solute clusters are formed in the alloy), under artificial time. The rolling properties of the alloy were reduced and the visible edge cracking was caused by the peak aging pretreatment. The solute re-precipitation during the subsequent aging process changed greatly with the solute state before deformation. The solute atom re-precipitation could compensate the strength loss and reduce the crystal defect. Compared with T6 treatment, the strength of samples treated by natural aging and under-artificial aging can be increased by 20-40% after subsequent aging, and the strength of samples treated by peak artificial aging can be increased by 40-50%, but the plasticity is very small. The samples pretreated by less artificial aging have the best strength and plasticity. Pre-aging before rolling has a great influence on the precipitation reaction of the subsequent aging process. The precipitation reaction types of the samples after natural aging pretreatment are similar. The difference is the total amount of precipitation phases formed in each precipitation reaction process. The precipitation reaction of the samples after peak artificial aging pretreatment is not obvious. Two types of precipitates are formed in the samples pretreated by natural aging after aging: the discrete strip Q "phase and the long and curved precipitates at the interface of dislocation cells. After subsequent aging, the precipitates in the samples pretreated by peak aging contain monoclinic beta phase before rolling, but there is a significant loss of order. After subsequent aging, the aluminum matrix is in a high strain state and the Q'type precipitates are still surrounded by a large number of dislocations.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.21
【参考文献】
相关期刊论文 前1条
1 季凯;祖国胤;姚广春;;一种新型可焊耐蚀6×××系铝合金材料[J];中国有色金属学报;2010年10期
，本文编号：2219725
本文链接：https://www.wllwen.com/kejilunwen/jinshugongy/2219725.html
教材专著
