【作者】 蒋显全；

【导师】 李宁；

【作者基本信息】 四川大学 ， 材料学， 2006， 博士

【摘要】 空调技术进步向着省能源、大功率和小型化方向发展，要求热交换器的高性能化、小型化和低成本，这就促使空调热交换器用铝箔厚度更薄、综合性能更高。本文作者采用铸轧工艺开发了新型薄壁高性能Al0.2Mn0.3Fe-H26铝箔来替代传统的纯铝系列翅片铝箔，其综合力学性能优于传统纯铝系列翅片铝箔，可满足变薄拉伸和ECO高速冲制等新技术要求，并以每月500吨的产量向市场供货。但生产过程中常出现力学性能波动、晶粒粗大等问题。为此，本文借助TEM、SEM、XRD、ODF、OM、DSC、杯突试验、室温和高低温环境力学性能测试等手段，针对铸轧工艺制备Al0.2Mn0.3Fe合金铝箔的关键工序：铸轧板坯均匀化处理、铝箔最终退火过程和高低温环境中的力学性能、组织的变化规律和机理进行了深入研究。揭示了这些工艺方法对翅片铝箔力学性能和组织影响的规律并从理论上进行了深入的探讨。取得了若干对工程应用有直接指导意义的研究成果，发现了诸如Al0.2Mn0.3Fe铝箔在退火过程中存在“临界再结晶温度现象”、H19、H26和0状态铝箔高低温性能变形规律区别较大、铝箔纤维晶粒在极低温度下转变为细小等轴晶粒等新现象，并对上述现象进行了解释。主要研究成果如下：1、通过对Al0.2Mn0.3Fe-H19状态最终退火过程中的性能、织构、组织和各向异性变化规律研究表明：（1）、Al0.2Mn0.3Fe-H26铝箔的最佳退火工艺为：退火温度为255℃×7～22h。可获得抗拉强度为140～145MPa、伸长率为13～15.1％、杯突值≥5.8mm，可满足拉深减薄和EGO等高速冲制翅片铝箔的要求。（2）、发现Al0.2Mn0.3Fe铝箔退火过程中存在“临界再结晶温度现象”：Al0.2Mn0.3Fe铝箔在低于并靠近再结晶温度退火时，出现综合力学性能过低，其再结晶晶粒呈现出异常粗大现象，该现象被本文命名为“临界再结晶温度现象”。这种现象是回复和再结晶竞争的结果，回复时间过长，用于再结晶的残余储存能少，单位体积内再结晶形核数过少。再结晶晶粒长大过程中，纤维晶粒中的残余储存能驱使再结晶晶粒持续长大到再结晶晶粒相互接触时停止长大。其效应类似于临界冷变形量下出现的粗大晶粒和较低综合力学性能现象；临界再结晶温度略低于并靠近传统意义上的再结晶温度。“临界再结晶温度现象”是造成工业生产中最终退火过程中出现综合力学性能过低，晶粒粗大的主要原因。（3）、发现铝箔退火过程中存在很强的“薄板尺寸效应”：Al0.2Mn0.3Fe铝箔在再结晶温度以上退火时，较高温度退火比较低温退火后的晶粒更细小，综合力学性能更优良。其原因是：退火温度越高单位体积中再结晶形核数越多；晶粒长大过程中由于铝箔厚度<再结晶晶粒直径，再结晶晶粒由球状变为圆柱状，晶粒晶界露出铝箔上下两表面而成为沟槽状，这种沟槽晶界阻碍再结晶晶粒长大，再结晶晶粒之间的相互吞噬不能进行。（4）、翅片铝箔的各向异性对退火温度比较敏感。当退火温度为225～260℃时强度和伸长率的各向异性最小，有利于提高翅片铝箔的深冲性能并减少冲制过程中的裂纹倾向。2、通过对Al0.2Mn0.3Fe铝箔高低温性能和组织的研究表明：（1）、发现铝箔同一种合金不同热处理状态的高低温性能变化趋势有较大区别：三种状态的屈服强度和断裂强度都是随拉伸试验温度的不断升高而逐渐降低，区别在于B19和H26状态在-66℃以下的低温拉伸试验时，断裂强度大于屈服强度，在70℃以上的高温拉伸试验时，屈服强度高于断裂强度。而0状态无论温度高低断裂强度始终高于屈服强度。三种状态的伸长率变化趋势在室温以上随温度的升高而增加；但室温以下有较大区别，H19在室温以下伸长率随温度下降略有下降，在-70℃附近开始上升，-175℃回升到室温的1.4倍；0状态在室温以下随温度的降低基本不变；H26状态在室温以下的伸长率随试验温度的逐渐下降而快速提高，在-170℃的伸长率达到室温的2.4倍，出现了低温异常优良塑性。（2）、发现在≤-170℃低温下，铝箔纤维晶粒转变成许多细小等轴晶粒，冷变形过程中产生的位错大量消失，并对其转变行为进行了描述和解释：本文认为在低温下原子间距收缩促使晶粒收缩，引起位错向晶界、相界和稠密位错墙（DDW）滑移。低温下异号位错难以对消，滑移到晶界或相界的位错加宽晶界界面，在晶界形成明显沟槽、台阶并使晶界宽化。而聚集到DDW的位错，加大DDW两侧晶粒的取向差，促使DDW转变成晶界。晶粒内众多的DDW转化为晶界后，纤维晶粒转化为许多细小等轴晶粒，温度越低上述趋势越明显。晶界的明显沟槽、台阶和微裂纹降低铝箔的伸长率，细小等轴晶粒提高铝箔的强度和伸长率，并抵消了由于宽化晶界和尖锐边角对伸长率降低的影响部分。（3）、H26状态在室温以下随温度下降伸长率升高的原因：经过退火充分回复后的H26铝箔，晶粒内异号位错全部对消，同号位错聚集成位错墙形成多边化形貌并伴随少量细小亚晶。在低温下，晶粒收缩导致退火过程中形成的多边化形貌转化为细小等轴晶粒，温度越低这种趋势越明显。当温度降低至-170℃时，纤维晶粒转变为细小等轴晶粒。这些细小等轴晶粒无尖锐边角，晶界没有沟槽、台阶和微裂纹存在，晶粒之间平滑过渡，这是低温拉伸时H26状态伸长率升高的主要原因。（4）、研究Al0.2Mn0.3FeH26翅片铝箔高低温性能具有广泛的应用价值。第一，为铝箔在不同环境下使用提供力学性能参考指标，指导人们正确使用铝箔。同时为铝箔加工工艺的制定提供力学性能参考。第二，H19和H26状态在70℃以上拉伸时，断裂应力只有屈服应力的55～95％。H26状态翅片铝箔在亲水处理过程中应控制张应力不超过24MPa，过大张力引起箔带的塑性变形，可能造成生产过程中翅片铝箔的力学性能改变，严重时甚至引起箔带断裂。第三，H26状态翅片铝箔在-45℃和50℃两温度点的抗拉强度相差21MPa，已超过标准许可波动范围，说明同一铝材在不同环境温度下测试的力学性能结果有较大差别，这种差别足以造成商业纠纷和经济损失。为此，建议国家有关部门立项研究铝材在不同温度下的力学性能，按温度分段（如每隔30～40℃）制定力学性能标准值。3、对铸轧坯料均匀化过程的组织变化规律研究表明：Al0.2Mn0.3Fe铸轧板带均匀化前的第二相呈粗大枝晶状、针状、网状和骨骼状，其边角较尖锐。铸轧板坯经430℃×4h均匀化处理后，枝晶状、针状、网状和骨骼状第二相大量减少，增加了大量球状细小弥散的第二相。经EPMA、XRD和单晶电子衍射分析，均匀化前的枝晶和骨骼状等粗大第二相主要是Al₆（Fe Mn），均匀处理后的细小球状第二相主要是Al9Fe_0.84Mn_2.16Si和Al₆Fe。在220～390℃均匀化处理，Al₆（Fe Mn）相溶解和球化不充分，Al₉Fe_0.84Mn_2.16Si相析出较少；在470～610℃均匀化，大量Al₆（Fe Mn）相都溶于基体中，Al₉Fe_0.84Mn_2.16Si等细小第二相析出量减少，均匀化温度越高，这种趋势越明显。均匀化温度为420℃时，保温时间即使长达40h，均匀化后的铸轧板坯晶粒尺寸与均匀化前接近。当均匀化温度达到450℃时，均匀化后铸轧板坯有个别粗大晶粒，≥550℃均匀化后全部为粗大晶粒。综合考虑：Al0.2Mn0.3Fe合金铸轧板坯的最佳均匀化工艺为420～430℃×4h。更多还原

【Abstract】 With the development of air-condition characterized by low energy consumption, large power and miniature, the high-powered, miniaturized and low-cost heat exchanger must be developed. Therefore, Al foil with thinner and higher comprehensive property are required. To meet this requirement, this paper developed a new A10.3Mn0.4Fe-H26 heat exchange foils produced by casting following rolling, whose comprehensive property is better than that of traditional pure Al foils. In addition, this new Al foils can meet the requirement of coining processing, such as attenuation, stretching and ECO, and its output reaches 500t per month. However, during the practical process of production, there existed the fluctuation of mechanical properties and abnormal coarsening of some grains. By means of TEM, SEM, XRD, ODF, OM, DSC, Cupping Test and Tensile Test at different temperature, the paper investigated the key processing technology in producing A10.3Mn0.4Fe-H26 foils by casting following rolling, including the homogeneous treatment of the as-forged slab and the heat treatment of the wing foils as well as the change trend of the mechanical property, microstructures, texture and anisotropic property of the foils. The effects of different treatment on the property and microstructures were revealed. Based on these work, the paper drew several wonderful results and revealed some new principals in A10.3Mn0.4Fe-H26 heat exchange foils, such as the critical recrystallized temperature in the annealing of Al foils, the thin-wall effects and its inhabitation of the recrystallization and coarsening of the grains, the increasing elongation ratio of Al-based H26 wing foils with the decreasing temperature and the turning of fibrous grains to fine equiaxed grains at low temperature. The paper tried to explain these phenomena and drew some common conclusions as following:1. The study of evolution of the property, texture and microstructures and the anisotropic property of the A10.3Mn0.4Fe-H26 foils during the last annealing showed:（1） For the A10.3Mn0.4Fe-H26 foils annealed at the optimal temperature 255□for 7～22h, the tensile strength （σ_b） is about 140～145MPa, the elongation ratio （5） is about 13～15.1%, and the Cupping value （Er） is GE 5.8mm, which can satisfy the needs of new techniques such as attenuation, stretching and ECO.（2） There existed the Critical Recrystallized Temperature Effects （CRTE） in the A10.3Mn0.4Fe-H26 foils during annealing.Being annealed at 330（?） for 22h, the mechanical properties of A10.3Mn0.4Fe-H26 foils are not so good. Microstructures analysis reveals that the recrystallized grains are abnormally coarsening. This result is named Critical Recrystallized Temperature Effects （CRTE） in this paper.The paper confirmed that CRTE originates from two main reasons. Firstly, if the recovery time is too long, the drive energy will be consumed. Therefore, the residual energy for nucleation and recrystallization is inadequate and the amount of nuclei in unit volume is less. Secondly the orientation difference between the recrystallized grains and fibrous grains is bigger and during the grains coarsening, the residual energy saved in fibrous grains can drive the constantly growth of recrystallized grains until they intersect. This is similar to the occurrence of coarse grains and low mechanical properties when the amount of cold-deformation is below critical value. The paper confirmed that the critical recrystallized temperature is a little lower than the traditionally critical recrystallized temperature.（3） The paper revealed the thin-wall effects during annealing of the A10.3Mn0.4Fe-H26 foils. Being annealed at higher temperature, the grains become finer at the higher temperature and the mechanical properties are better. There are two reasons for the result. Firstly, the higher of the annealing temperature, the more of recrystallized nuclei is. Secondly, because the size of the recrystallized grains is greater than thickness of the foils, during annealing the recrystallized grains exposed on the two rolling planes are changed from spherical to cylindrical and along the cross-section of the foil, and turned into the groove. As a result, the growth of grains is inhibited.（4） The anisotropic property of the Al-based wing foils is sensitive to the annealing temperature. Being annealed at 225～260（?）, the anisotropy of strength and elongation is minimum, which can improve the deep cupping property and decrease the tendency of cracking.2. The study of the mechanical property and microstructures of A10.3Mn0.4Fe foils deformed at high temperature and low temperature showed:（1） There existed remarkable difference between the mechanical properties at different temperature of the same Al-based foils subjected to different heat treatment. The yield strength and tensile strength of Al-based foils subjected to H19, H26 and 0 treatment both decrease with the increasing temperature, but the tensile strength of Al-based foils subjected to H19 and H26 is higher than the yield strength when the deformation temperature is below -66（?）. When the deformation temperature is above 70（?）, the tensile strength is lower than the yield strength. For Al-based foils subjected to 0 treatment, the tensile strength is always greater than the yield strength.When the temperature is above room temperature,δof Al-based foils subjected to H19,H26 and 0 treatment increase with the increase of temperature. Below the room temperature, For Al-based foils subjected to H19 treatment,δslightly decreases with decreasing temperature up to about] -66（?） and then increases with the further decreasing temperature and reaches 5.4%, 1.4 times as many as that at room temperature. For Al-based foils subjected to 0 treatment,δkeep constant with decreasing temperature. For Al-based foils subjected to H26 treatment,δincreases remarkably with decreasing temperature and reaches 28.5% at -175（?）, 2.4 times as many as that at room temperature, showing abnormal plasticity at low temperature.（2） The paper found that when deformed below -170（?）, the fibrous grains in Al-based foils turn into many fine equiaxed grains and dealt with the process and mechanism of fracture of those fibrous grains.The paper argued that at low temperature the distances between atoms decrease, leading to the slipping of dislocations to the grains boundary, phase interfaces and dislocation walls. But at low temperature, unlike dislocations are difficult to offset. Therefore, those dislocations slipped to the grains boundaries and phase interfaces form obvious groove and pedestal sit, widening the grain boundary. Those dislocations aggregated at the DDW increase the orientation decrement of the grains and thus make the DDW turn into grains boundaries. After lots of DDW turn into grains boundaries, the fibrous grains are divided into many finer equiaxed grains. This tendency becomes more obvious with decreasing temperature.The obvious groove and pedestal sit at grain boundaries as well as microcrack will decrease the elongation, but the fine equiaxed grains induced by DDW will increase the strength and elongation, compensate the decrease of strength and elongation induced by enlarged grains boundaries and polw grooves.（3） After the H26 treatment, foils are fully annealed. Therefore, the unlike dislocations completely vanish, only identical dislocations gather and form the dislocation wall, leading to polygonization accompanying with the occurrence of some fine subgrains. At low temperature, the polygonized microstructures turn into fine equiaxed grains. The tendency becomes more obvious with decreasing temperature. At -170（?）, most of the fibrous grains turn into fine equiaxed grains. As a result, the fine equiaxed grains have t no polw grooves or steps, increasingδat low temperature.（4）The researches on mechanical property of A10.3Mn0.4Fe foils at high temperature and low temperature are of important engineering value, providing the data of mechanical properties at different temperature and guiding the selection of Al foils. Above 70（?）, the fracture strength of H19 and H26 are only 55～95% of its yield strength. During the hydrophilic treatment of H26 foils, the stretching force must be lower than 24MPa. Otherwise, the plastic deformation will occur, leading to the change of the mechanical property and even the fracture.In addition, the difference between the tensile strength at -45（?） andσb at 50（?） of H26 foils amounts to 21MPa, exceeding the permission fluctuation of standard. This reveals that there exists a remarkable difference between mechanical properties of Al foils tested at different temperature. This difference is so big as to bring about business dissension. As a result, we suggest that the government support the study about mechanical properties of Al foils at different temperature and build the standards.3. The study of variations of the microstructures of the casting following rolling during homogeneous treatment showed:The second phases of the as rolled plates before homogenization is tree-like, or acicular, or reticular, or skeleton-like with the sharp interfaces. After being homogenized at 430（?） for 4h, the tree-like, acicular, reticular and skeleton-like microstructures are remarkably reduced and lots of dispersed spherical second phase are produced in the whole matrix. EPMA, XRD and single crystal diffraction analysis determine that the coarse second phase before homogenization is mainly Al₆（Fe Mn）. After homogenization, the fine spherical second phase is mainly A19FeO.84Mn2.16Si. Being homogenized at 220～390（?）, the solution and spheroidization of Al₆（Fe Mn） are inadequate and thus the A19FeO.84Mn2.16Si is less. With the increasing temperature to 470～610（?）, lots of Al₆（Fe Mn） phases are solved into the matrix and the amount of . A19FeO.84Mn2.16Si precipitated decreases. The higher the homogenization temperature, the more obvious this tendency.Being homogenized at 420（?）, even period of the annealing time is long to 40h, the size of grains is close to those before homogenization. Being homogenized at 450（?）, a few grains begin to coarsen and over 450（?）, almost all grains coarsen. As a compromise, the optimal homogenization temperature for A10.3Mn0.4Fe foils is 420～430（?） and the time is 4h.更多还原