【作者】 孙有平；

【导师】 严红革；

【作者基本信息】 湖南大学 ， 材料加工工程， 2009， 硕士

【摘要】 SiC颗粒增强铝基复合材料具有比强度和比模量高、耐磨性好等优点,但是其伸长率明显低于基体合金且SiC颗粒在基体合金中的分布均匀性不够理想。对其进行塑性变形,不仅可以提高复合材料的致密度,还可以改善SiC颗粒分布的均匀性,进而提高复合材料的强度,改善其塑性和韧性。以上相关报道较多,但对不同应力应变状态下SiC颗粒的运动及分布规律的研究工作尚无系统报道。本文采用实验室自有的坩埚移动式喷射沉积专利技术和粉末冶金技术制备了7090Al/SiCp（SiCp体积分数为15%）铝基复合材料锭坯,分别采取热挤压（三向应力）、等径角挤压（纯剪切应力）和楔形压制技术（单向压应力）对复合材料进行了塑性变形,研究了喷射沉积锭坯在塑性变形过程中的致密化行为、SiC颗粒的破碎、运动及再分布规律,得到了如下结论:（1）喷射沉积制坯过程中,SiC颗粒主要粘附于合金液滴的表面,造成SiC颗粒在合金液滴表面较多,内部较少,使SiC颗粒呈现层状分布特征。在挤压变形的三向应力作用下,这种层状分布特征难以消除,SiC颗粒在挤压棒材中呈条带状流线分布,横截面上则呈“年轮”分布特征。增大挤压比时,挤压棒材中SiC颗粒的分布趋于均匀。（2）采用P/M法制备了SiC颗粒均匀分布的7090Al/SiCp复合材料坯件,并进行热挤压实验,研究了SiC颗粒在热挤压变形过程中的分布特点,并与喷射沉积坯挤压结果进行了对比。实验结果表明:原始锭坯中的SiC颗粒分布越均匀,挤压棒材中SiC颗粒的分布也越均匀。在挤压过程中,SiC颗粒在基体合金中沿挤压方向呈定向分布特征,这是由热挤压变形时的应力特征决定的,但是没有形成SiC颗粒分布不均匀的条带组织;在挤压棒材的横截面上SiC颗粒分布的比较均匀,未出现年轮组织。挤压比为11时,挤压棒材中存在一定量合金粉末颗粒的结合界面,说明此时的挤压比不足以使合金粉末颗粒实现完全的冶金结合。提高挤压比至17以上时,合金颗粒结合界面逐渐消除,实现了冶金结合。（3）挤压态7090Al/SiCp复合材料的基体合金中存在大量短棒状的MgZn2相及圆形的CuAl₂相颗粒,MgZn₂粒子长约200nm,直径约60nm,分布在晶粒内部;CuAl₂相为球形粒子,尺寸不一,大的颗粒直径大约为420nm,小颗粒直径在40～60nm之间,主要分布在晶界上或近晶界区域。（4）研究了7090Al/SiCp挤压棒材的固溶及时效制度,确定了最佳固溶温度为475℃,固溶时间为1h。经过固溶处理后,第二相颗粒MgZn2及CuAl2粒子溶入到了基体合金中,复合材料棒材的力学性能为:σb=610MPa,δ=2.0%;再经过120℃/24h时效处理后,复合材料棒材的力学性能为:σb=765MPa,δ=1.5%。（5）研究了等径角挤压（ECAP）工艺对喷射沉积7090Al/SiCp复合材料棒材组织和性能的影响,结果表明:ECAP温度对变形行为的影响明显;SiC颗粒在等径角挤压时的剪切力作用下会被破碎,破碎的SiC颗粒之间产生的空洞在300℃下很难被基体合金填充;将挤压温度提高到350℃以上时,破碎的SiC颗粒之间的空隙逐渐被基体填充、粘合,并可在一定范围内随基体合金流动,分布均匀性明显提高。在本研究中最佳的ECAP温度为400℃。（6）以加工路径A、Bc、C,在400℃下对7090Al/SiCp复合材料进行了多道次等径角挤压。结果表明,按路径Bc进行挤压时的力学性能优异,经过4个道次的变形后,晶粒为等轴晶,晶粒尺寸为400nm;峰值时效处理后,棒材的抗拉强度及屈服强度分别为770MPa及575MPa,弹性模量为106.6GPa,伸长率为7.4%;SiC颗粒尺寸被显著细化,由初始状态时的10μm左右破碎至2μm左右。（7）基于对坯件进行多道次小变形累积实现大变形的思想,研究了大尺寸喷射沉积7090Al/SiCp复合材料锭坯（510mm×337mm×200mm）在楔形压制变形过程中SiC颗粒分布规律及孔洞变形行为。结果表明,在楔压过程中,坯料发生局部塑性变形,使喷射沉积坯中的孔隙发生剪切变形、闭合,最终实现坯件的致密化;SiC颗粒在压制力的作用下发生了转动,使SiC颗粒由沉积坯内的紊乱分布变为长轴垂直于压制方向的有序分布,但破碎效果不明显。更多还原

【Abstract】 Aluminum matrix composites reinforced with SiC particles are characteristic of high specific strength, high specific toughness and excellent abradability, but they exhibit much lower elongations than the matrices and the non-uniform distribution of SiC particles in the matrix. Plastic processing can elevate the compactability of the composites and promote the uniform distribution of SiC particles, contributing to higher strength, better plasticity and toughness. There are many reports on the topic mentioned above, while there is almost no systematic report on the regularities of the motion and distribution of SiC particles under different stess and strain states.In this dissertation, 7090Al/SiCp (the volume fraction of SiCpbillets were prepared by multi-layer spray co-deposition technique and powder metallurgy respectively and were successively deformed by different plastic processings such as hot extrusion, equal channel angular pressing and wedge pressing repectively. The compaction behavior, the fragmentation, the motion and the re-distribution of SiC particles in the as-deposited composite were systematically studied. The conclusions are drawn as follows:(1) SiC particles adhered mainly to the surface of the alloy droplets during deposition, leading to more SiC particles at the surface of the droplet and less in the inner. Thus, the distribution of SiC particles in the composite was characteristic of the layered feature. This layered feature of SiC particles was not removed by the following hot extrusion. The SiC particles were distributed like the streamline in the longitudinal direction, while the ring-like feature of the SiC particles was observed in the transverse direction. A higher extrusion ratio resulted in an more uniform distribution of SiC particles.(2) The distribution and the motion of SiC particles in the PM 7090Al/SiC_pcomposite billet during hot extrusion were also investigated detailedly and compared with the as-deposited billet. The more uniform the distribution of SiC particles in the PM billet, the more uniform of SiC particles in the as-extruded rod. There was still an order and directional distribution of SiC particles in the longitudinal direction, but there was no ring-like feature of SiC particles in the transverse direction in the as-extruded PM billet. The former was related to the stress state associated with hot extrusion. In addition, a more uniform distribution of SiC particles was observed in the as-extruded PM billet and no SiC segregation streamline occurred. With a small extrusion ratio (11), many obvious interfaces between powder and powder remained existent since the deformation stress was not large enough to achieve the metallurgical bond. Metallurgical interfaces were achieved with the extrusion ratio of 17.(3) There were a large amount of short rod-like MgZn2 and spherical CuA12 particles in the matrix of the as-extruded 7090Al/SiCp composite. The MgZn2 particles were mainly distributed within the grains with the length of about 200 nm, and the width of about 60 nm, while the CuA12 particles were mainly distributed at grain boundaries or the near areas with the diameter from 420 nm to 40-60 nm.(4) The solid solution and artificial aging processes of the as-extruded 7090Al/SiCp aluminum alloy matrix composite were systematically investigated. The best solid solution process was solutionized at 475℃for 1h. The particles of MgZn2 and CuAl2 were dissolved after the solid solution treatment and the composite in the solid solution state was characteristic of the ultimate strength and elongation of 610 MPa and 2.0% respectively, while that in the solid solution plus aging state exhibited the ultimate strength and elongation of 765 MPa and 1.5%.(5) Temperature had an obvious effect on the plastic behavior of the spray-deposited composite during equal chnnel angular pressing. The hard SiC particles were broken by the shear stress and many cavities between the broken SiC fragments occurred with the the pressing temperature of 300℃, which could not be filled with the matrix. With the pressing temperature of 350℃and 400℃, the cavities derived from the SiC breakup were filled with the matrix and flew with the matrix in a certain range. The optimal pressing temperature was 400℃.(6) Equal channel angular pressing was performed on the spray-deposited 7090Al/SiCp composite at 400℃with the routes of A, Bc and C and the channel properties and equiaxed grains with the average grain size of 400 nm were obtained from the fourth pass. The tensile strength, the yield strength, the modulus and the elongation of the composite after peak ageing treatment were 769MPa, 574MPa, 106GPa and 7.4% respectively.(7) On the basis of the conception that a large deformation could be obtained through the accumulation of many times of small deformation, the distribution of SiC particles and the deformation of the pores during the wedge pressing of the large dimension spray co-deposited 7090Al/SiC composite experienced by Bc had higher mechanical pressing resulted in the local deformation, which led to the shear deformation and the closure of pores. Ultimately the pores were eliminated and the densification was realized. The SiC particles rotated under the pressing force and exhibited an order distribution with the long axis perpendicular to the pressing direction.更多还原