液态模锻7055铝合金的组织与力学性能研究

发布时间：2018-05-12 04:08

本文选题：液态模锻 + 7055铝合金　；参考：《北京交通大学》2016年硕士论文

【摘要】：7XXX系铝合金中的7055铝合金具有密度小、韧性好、比强度高、加工成本低和容易成型等优良性能,已广泛用于航空、航天、交通及其他方面的结构件中。随着科技的进步和时代的快速发展,工业上对7055铝合金材料的综合性能提出了更高的要求。国内外许多学者和专家对7055铝合金的制备工艺、时效、均匀化、合金化等方面进行了深入研究,进展显著。目前通过液态模锻技术来制备7055合金及分析其组织和常规力学性能的研究,尚属国内空白。本文研究成果如下：(1)对液态模锻7055铝合金液锻态和热处理态试样的各特征位置组织性能的研究表明：热处理前同一液锻件低压时底部先凝固,所以底部晶粒最小,随压力增大顶部受压使晶粒压碎,致使试样顶部晶粒尺寸比底部变小。热处理后,各特征位置的微观组织均得到改善,从而提高了力学性能,特别是心部元素固溶到基体较充分,力学性能提高显著。(2)对不同压力对液态模锻7055铝合金液锻态和热处理态试样组织性能的研究表明：对于液锻后试样的同一位置随压力增大晶粒尺寸先减小再增大,然后呈减小趋势。热处理后的试样显微组织晶粒均增大,但析出的第二相起到了强化作用,固溶效果明显,对于显微组织晶粒尺寸,热处理状态下比液态模锻状态下均有所增大；随着压力的不断提高,晶粒尺寸开始时减小然后逐渐增大；随着压力的进一步增大,晶粒的尺寸呈现减小趋势。(3)对液态模锻7055铝合金液锻态试样表面粗糙度的检测分析研究表明：在上表面,由于低压时压头过冷度大加快上表面凝固速度,表面粗糙度随压力增大而下降,随着压力增大,压力使处于较高温度的上表面发生锻压变形,使表面粗糙度降低。在下表面,表面粗糙度随压力增大而持续下降,然后趋于稳定。在侧面,表面粗糙度随压力增大而基本稳定；在端面,表面粗糙度浮动较大。(4)对不同压力对液态模锻7055铝合金液锻态和热处理态常规力学性能的影响规律研究表明：热处理后的力学性能均比液锻态的性能有明显增加,其中硬度、拉伸强度、弯曲强度在各压力条件下提高的幅度比例基本一致,而冲击韧性波动较大,压力75MPa时提升最大。热处理前试样拉伸强度、弯曲强度、硬度达最高时的压力分别为125MPa、125MPa和75MPa,热处理后试样拉伸强度、弯曲强度、硬度最高时对应的压力分别为100MPa、125MPa和1OOMPa。热处理后的材料断裂韧性低压时随压力增大而提高,在50MPa压力以上时保持平稳。
[Abstract]:7055 aluminum alloy in 7XXX series has been widely used in aviation, aerospace, transportation and other fields because of its low density, good toughness, high specific strength, low processing cost and easy forming. With the progress of science and technology and the rapid development of the times, the industrial requirements for the comprehensive properties of 7055 aluminum alloy materials are higher. Many scholars and experts at home and abroad have made great progress in the preparation, aging, homogenization and alloying of 7055 aluminum alloy. At present, the preparation of 7055 alloy by liquid die forging technology and the analysis of its microstructure and conventional mechanical properties are still blank in our country. The research results are as follows: (1) the microstructure and properties of liquid die forging 7055 aluminum alloy samples in liquid forging and heat treatment state are studied. The results show that the bottom of the same liquid forging is solidified at low pressure before heat treatment, so the grain at the bottom is the smallest. The grain size at the top of the sample is smaller than that at the bottom. After heat treatment, the microstructure of each characteristic position was improved, which improved the mechanical properties, especially the solid solution of the core elements to the matrix. The study on the microstructure and properties of liquid die forging 7055 aluminum alloy under different pressure shows that the grain size decreases first and then increases with the increase of pressure. Then it tends to decrease. After heat treatment, the microstructure grains of the samples increased, but the second phase of precipitation played a strengthening role, and the effect of solid solution was obvious. The grain size of the microstructure in the heat treatment state was larger than that in the liquid die forging state. With the increasing of the pressure, the grain size decreases at first and then increases gradually, and with the further increase of the pressure, The analysis of the surface roughness of liquid die forging 7055 aluminum alloy shows that, on the upper surface, the solidification rate of the upper surface is accelerated because of the high undercooling of the pressure head at low pressure. The surface roughness decreases with the increase of pressure, and with the increase of pressure, the upper surface at higher temperature is deformed by forging, and the surface roughness decreases. On the lower surface, the surface roughness decreases continuously with the increase of pressure, and then tends to stabilize. On the side, the surface roughness is basically stable with the increase of pressure; on the end surface, The effect of different pressure on the conventional mechanical properties of liquid and heat treated 7055 aluminum alloy was studied. The results showed that the mechanical properties of 7055 aluminum alloy after heat treatment were obviously higher than those of liquid forging, and the hardness of them was higher than that of liquid forging. The tensile strength and flexural strength are basically the same under various pressure conditions, while the impact toughness fluctuates greatly, and the maximum increase is under pressure 75MPa. Before heat treatment, the tensile strength, bending strength and hardness were 125 MPA and 75 MPA, respectively. After heat treatment, the tensile strength, bending strength and the corresponding pressure at the highest hardness were 100 MPA and 1 OOMPA, respectively. After heat treatment, the fracture toughness of the material increases with the increase of pressure at low pressure, and remains stable above the 50MPa pressure.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG319

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