7050铝合金H型截面长轴锻件成形工艺优化及淬火残余应力消除研究

发布时间：2018-09-06 15:08

【摘要】：随着航空航天工业向轻量化发展,带有纵横内筋结构的H型截面铝合金锻件得到广泛的应用。这类构件由于承载大部分载荷且所处工作环境极为恶劣,被要求具有较高的尺寸精度、较好的组织流线分布及优良的综合力学性能。因此,对这类铝合金构件的成形工艺、热处理工艺及后期淬火残余应力消除工艺的研究对提高该类合金锻件的性能至关重要。论文采用热模拟实验、热模锻生产试验、常温力学拉伸、断裂韧性实验、显微组织观察(OM、SEM)、残余应力检测实验、冷压实验及有限元数值模拟,研究了7050铝合金H型截面锻件热模锻成形工艺,研究了固溶温度、淬火介质以及淬火转移时间对7050铝合金试件中第二相粒子、晶粒结构、材料强度及断裂韧性的影响,研究了7050铝合金构件在不同淬火工艺下的残余应力大小、分布及规律,研究了不同模压工艺对7050铝合金构件淬火残余应力的影响。相关结论如下:(1)采用Gleeble试验机对7050铝合金在温度300-450℃,应变速率为0.01-10s-1条件下对7050铝合金进行热压缩试验,得到了合金不同变形情况下的真实应力-应变曲线。对热压缩实验数据进行回归分析,基于双曲正弦Arrhenius方程,建立了用Z参数表示的7050铝合金本构关系。该本构模型为后期的数值模拟分析奠定理论基础。(2)基于响应面优化算法,对7050铝合金H型截面锻件热模锻成形工艺参数进行优化,将优化后的工艺参数应用到实际生产,获得成形质量完好的模锻件。通过对锻件热模锻成形中出现的充填不满、流线穿流、变形不均匀等缺陷问题的形成机理进行分析,结合数值模拟与响应面法(RSM),对热模锻成形工艺参数进行优化,得到锻件成形最优工艺参数。(3)研究和揭示了不同固溶温度对7050铝合金组织和性能的影响。7050铝合金热处理过程中大部分的第二相粒子会随着固溶处理的进行逐渐的融入到基体中去,随着固溶温度的升高,第二相粒子逐渐减少而后趋于稳定。然而随着固溶温度的升高,晶粒发生再结晶的比例也会增大。因此,随着固溶温度升高,合金的强度以及断裂韧性先升高后降低,在固溶温度为470°C时达到峰值,此时合金的抗拉强度(σb)、屈服强度(σ0.2)以及断裂韧性(KIC)分别为567MPa、512MPa和37.2MPa·m1/2。(4)研究和揭示了不同淬火介质、淬火转移时间对7050铝合金组织和性能的影响。不同淬火介质、淬火转移时间对7050铝合金淬火过后第二相粒子体积分数有较为明显的影响,但对淬火过后的组织形态影响不大。四种淬火介质中盐浴淬火工艺下的淬火过后的铝合金中的第二相粒子体积分数最小,因而其时效过后的力学性能最好。其次是淬火介质为水时及淬火介质为20%PAG溶剂;空冷状态下的淬火过后的铝合金中的第二相粒子体积分数最大,因而其时效过后的力学性能最差。另外,水淬工艺下,随着淬火转移时间的增加,淬火过后合金中第二相粒子逐渐增多,时效后合金的力学性能逐渐下降。(5)研究和揭示了不同淬火介质、淬火转移时间对7050铝合金H型截面锻件淬火后残余应力的影响。锻件淬火后表层残余应力为拉应力,芯部为压应力。锻件淬火残余应力主要集中在过渡圆角区域,其随着锻件筋板的厚度增加而增大。另外,锻件表面淬火残余应力随着过渡圆角的增大而增大;芯部淬火残余应力随着过渡圆角的增大反而减小。四种淬火介质当中,淬火介质为空气时锻件淬火残余应力值最小,其次是20%PAG溶剂,水及NaCl溶液下的锻件淬火残余应力相对较高。随着淬火转移时间的增大,锻件截面过渡圆角区淬火残余应力值逐渐减小。(6)研究了不同冷压工艺对7050铝合金H型截面锻件淬火残余应力的影响。通过数值模拟确定先筋顶圆角同时下压,下压结束后再对锻件腹板部分进行冷压是最佳的冷压工艺。优化后的模具使得锻件整个截面淬火残余应力得到有效的控制,锻件残余应力消减到40 Mpa以下。随着模压量的增大,锻件截面过渡圆角区残余应力先减小后增大,在模压量为3%时达到最低值。模压后的试件表面残余应力实验结果与数值模拟结果比较吻合,实验测试值与数值模拟值误差在30MPa以内,说明采用数值模拟的方法测试试件淬火残余应力有着较高的精度。
[Abstract]:With the development of aerospace industry toward lightweight, H-shaped aluminum alloy forgings with longitudinal and transverse internal ribs have been widely used. These components are required to have high dimensional accuracy, better microstructure and streamline distribution, and excellent comprehensive mechanical properties because they bear most of the loads and work in very bad environment. The forming process, heat treatment process and Post-Quenching residual stress relief process of quasi-aluminium alloy components are very important to improve the properties of such alloy forgings.Thermal simulation test, hot die forging production test, mechanical tensile test at room temperature, fracture toughness test, microstructure observation (OM, SEM), residual stress detection test and cold pressing test are used in this paper. The hot die forging process of 7050 aluminum alloy H-section forgings was studied by means of finite element numerical simulation. The effects of solution temperature, quenching medium and quenching transfer time on the second phase particles, grain structure, material strength and fracture toughness in 7050 aluminum alloy specimens were studied. The residual stress of 7050 aluminum alloy components under different quenching conditions was also studied. The influence of different molding process on the residual stress of 7050 aluminum alloy was studied. The conclusions are as follows: (1) The hot compression test of 7050 aluminum alloy was carried out by Gleeble testing machine under the conditions of temperature 300-450 C and strain rate 0.01-10s-1, and the true deformation of 7050 aluminum alloy was obtained. The constitutive relation of 7050 aluminum alloy expressed by Z parameter is established based on the hyperbolic sinusoidal Arrhenius equation. The constitutive model lays a theoretical foundation for the later numerical simulation analysis. (2) Based on the response surface optimization algorithm, the hot die forging worker of 7050 aluminum alloy H-section forging is studied. The process parameters were optimized, and the optimized process parameters were applied to the actual production to obtain the forgings with good forming quality. The forming mechanism of defects such as filling dissatisfaction, streamline crossflow and uneven deformation in hot die forging was analyzed, and the forming process of hot die forging was studied by numerical simulation and response surface methodology (RSM). (3) The effects of different solution temperatures on the microstructure and properties of 7050 aluminum alloy were studied and revealed. Most of the second-phase particles will be gradually incorporated into the matrix with the solution treatment, and the second-phase particles will increase with the solution temperature. As the solution temperature increases, the strength and fracture toughness of the alloy increase first and then decrease, reaching a peak value at 470 C, at which time the tensile strength (_b), yield strength (_0.2) and fracture toughness of the alloy reach a peak value. The effects of quenching transfer time on the microstructure and properties of 7050 aluminum alloy with different quenchants were studied and revealed. The effect of quenching transfer time on the volume fraction of the second phase particles after quenching in different quenchants was obvious, but the morphology of the second phase particles after quenching was affected. The volume fraction of the second phase particles in the aluminum alloy quenched by salt bath quenching in four kinds of quenching media is the smallest, so the mechanical properties after aging are the best. In addition, with the increase of quenching transfer time, the second phase particles in the alloy increase gradually after quenching, and the mechanical properties of the alloy decrease gradually after aging. (5) The effect of quenching transfer time on the mechanical properties of 7050 aluminum alloy H-section forgings quenched by different quenchants was studied and revealed. The residual stress in the surface layer of the forging is tensile stress and that in the core is compressive stress. Among the four quenchants, the value of quenching residual stress in air is the smallest, followed by 20% PAG. The value of quenching residual stress in water and NaCl solution is relatively high. The influence of different cold-pressing processes on the quenching residual stress of 7050 aluminum alloy H-section forgings was studied.The numerical simulation showed that the best cold-pressing process was to press the fillet of the top of the rib at the same time and then cold-pressing the web part of the forgings after the end of the cold-pressing.The optimized die could effectively control the quenching residual stress of the whole section of the forgings and the forgings. The residual stress decreases below 40 Mpa. With the increase of die pressure, the residual stress in the transition fillet of the forging section decreases first and then increases, reaching the lowest value when the die pressure is 3%. The numerical simulation method is used to test the quenching residual stress of specimens with high accuracy.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG319;TG156.3

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