【作者】 陈登斌；

【导师】 赵玉涛；

【作者基本信息】 江苏大学 ， 材料学， 2012， 博士

【摘要】 随着铝合金在航空航天、汽车、高速列车、电子等领域的广泛应用,对铝合金材的性能提出了更高的要求。材料复合化是继合金化之后的又一重要强化手段。尤其是原位内生颗粒增强铝基复合材料,由于其本身的优点已经成为复合材料领域的研究热点。如何控制原位内生增强颗粒在基体中的尺寸、形貌、分布是复合材料制备中的关键,也是目前复合材料向产业化应用的瓶颈之一。因此,通过优化原位反应体系、制备工艺来控制复合材料的组织和性能具有重要的理论意义与现实意义。论文的思路基于以下三点：一、通过稀土钇的作用,细化基体合金的晶粒,提高其综合性能；二、通过优化反应体系及声磁场等手段对复合材料的组织实现控制,包括增强颗粒的尺寸、分布、形貌；三、将稀土钇与声磁耦合场协同作用,达到复合材料高强高塑性的目的。研究了稀土钇对基体合金7055A1、6070A1的影响,结果表明,稀土钇可有效细化基体合金的晶粒,且稀土的最佳添加量为0.25wt.%。当稀土加入量超过0.25wt.%时,晶粒反而粗化,且稀土化合物粗化,形貌变为长针状。对Al-K2TiF6、Al-K2ZrF6-Na2B4O7、Al-K2TiF6-KBF4反应组元进行工艺优化,并分别制备了Al3Ti/6070Al、Al2O3/Al、TiB2/7055Al复合材料。对于Al-K2TiF6反应组元,合理的工艺为先复合再添加Mg等合金元素完成合金化,且反应时间不应超过10 min,反应温度控制在730-750℃为宜。对于Al-K2ZrF6-Na2B4O7反应组元,反应温度为850℃,其反应机理为反应-溶解-析出。对于Al-K2TiF6-KBF4反应组元,合理的工艺为先加Mg再复合,反应温度为850℃,反应时间不宜超过20 min。在超声场下制备了Al3Ti/6070AL、Al2O3/Al、TiB2/7055Al复合材料。实验结果表明,Al3Ti/6070Al、Al2O3/Al复合材料,随着超声功率、作用时间的增加颗粒数量减少,认为其机理为驻波场机理及声空化机理。对于Al3Ti/6070Al复合材料超声的最佳功率为1.6kW,最佳作用时间为3 min,A13Ti颗粒的尺寸由原来的2-5μm细化至1μm左右,形貌变为小块状、粒状;对于Al2O3/Al复合材料超声的最佳功率为0.60 kW,最佳作用时间为2 min,超声显著提高了复合材料A1203颗粒的收得率；利用水淬法研究了超声场下混合盐法制备TiB2/7055Al复合材料的过程机制,认为反应过程可分为四个阶段,超声场在第二阶段对反应过程起到了显著的促进作用,TiB2颗粒随超声功率的增加而逐渐细化,特别是当超声功率达到1.6kW时,出现大量纳米级TiB2颗粒。在低频旋转磁场下,研究了Al3Ti/6070Al、TiB2/7055A1复合材料的制备工艺。结果表明,对于Al3Ti/6070Al复合材料,随着励磁电流、频率的不同可得到颗粒均匀分布及梯度分布两种不同类型的复合材料,认为,当励磁电流200A、频率小于5Hz、作用时间为3-5 min时,得到尺寸细小、熔体内外分布相对均匀的Al3Ti/6070Al复合材料；而增大频率或电流时,作用时间必须相应减少；增大励磁电流、频率以及作用时间均能得到A13Ti颗粒呈梯度分布的复合材料。基于上述实验,推测采用磁场连续作用方式制备复合材料时,熔体中存在二次流。利用水淬法采用间歇作用方式,研究了低频旋转磁场下TiB2/7055Al复合材料的过程机制,认为磁场在反应初期对反应过程起到了有益的促进作用。制备TiB2/7055Al复合材料时,磁场频率对复合材料微观组织影响不大,当频率较小(<5Hz)时TiB2颗粒尺寸无明显的变化,只有当频率达到5 Hz时,颗粒尺寸趋向一致,颗粒形貌发生明显的“圆钝化”。在声磁耦合场下制备了Al3Ti/6070Al、TiB2/7055Al复合材料。结果表明,声场耦合场下所得的A13Ti颗粒尺寸细小,分布均匀。当超声功率为1.6 kW时,约72.4%的A13Ti增强颗粒处于0.2～0.5μm之间,处于0.8-1.2μm之间的颗粒减少至约1.6%。声场耦合场下制备Al3Ti/6070Al时,颗粒尺寸随粉末加入量的增加有一定程度的增大,颗粒形貌由粒状、小块状逐步向块状、片层状或短棒状发展。声磁耦合场下连续作用合成TiB2/7055Al时,超声功率为0.8 kW即能观察到大量纳米级TiB2颗粒,尺寸约为80-100 nm,纳米TiB2颗粒呈团聚状态。声磁耦合场下间歇作用合成TiB2/7055Al时,得到均匀分布的亚微米TiB2增强颗粒。添加稀土钇基体力学性能结果表明,7055A1合金的强度、硬度随稀土钇加入量的增加而下降,伸长率上升；6070A1合金的强度、伸长率均随钇含量的增加先增大后减小。复合材料的力学性能结果表明,超声场下A12O3/Al复合材料的抗拉强度、伸长率随超声功率、超声时间的增加先增大后减小,最佳作用参数分别为0.6 kW、2 min；耦合场下Al3Ti/6070Al、TiB2/7055Al复合材料拉伸性能均优于单一场；声磁耦合场与稀土协同作用可显著抑制复合材料伸长率随体积分数的下降。更多还原

【Abstract】 With increasingly application in the aerospace, automotive, high-speed trains, electronics and other fields, aluminum alloys with higher properties are required. Compounding is another important strengthening method expect for alloying. In-situ particle reinforced aluminum matrix composites due to its own merit, have become a hot research in the composites field. How to control the size, morphology and distribution of in-situ reinforced particles in the matrix is the key techniques in the preparation of composites and also is currently one of the bottlenecks for industrialization application. Therefore, the control of the microstructure and properties of the composites by selecting the reaction systems and optimizing processing conditons have important theoretical and practical significance. The frame of the paper is based on the following three ideas:1. refine the grain of the matrix alloy in order to improve its comprehensive properties by adding rare earth yttrium; 2. control the microstructure of the composites, including the size, distribution and morphology of the particles by optimizing the reaction system or applying ultrasonic and magnetic fields; 3. achieve high strength and high englation by combining with above-mentioned methods.The effects of rare earth yttrium on mircrostructure of 7055A1,6070A1 matrix alloys were investigated. The results show that the addition of the rare earth yttrium can effectively refine the grains and the optimal addition amount of rare earth is 0.25% (mass fraction). When the yttrium addition is more than 0.25%, grain coarsening takes place. Moreover, yttrium-containing compound also coarsen and the morphology become long needle-like.The process optimization for Al-K2TiF6, Al-K2ZrF6-Na2B4O7 and Al-K2TiF6-KBF4 component were studied, and Al3Ti/6070Al, A12O3/Al, TiB2/7055Al composites were fabricated. The results show that the reasonable process for Al-K2TiF6 component are synthesis first then alloying with Mg, reaction time less than 10 min and temperature 850℃. For Al-K2ZrF6-Na2B4O7 component, the proper reaction temperature is 850℃, and its reaction mechanism is reaction-solution-precipitation. For Al-K2TiF6-KBF4 component, the best process are alloying with Mg first then synthesis, reaction temperature 850℃and reaction time less than 20 min.Al3Ti/6070Al, Al2O3/Al, TiB2/7055Al composites were successfully prepared under ultrasonic field. The experiment results show that as the ultrasonic power and reaction time increase, the number of particles in Al3Ti/6070Al and Al2O3/Al composites is significantly reduced, which can be explained by standing wave mechanism and cavitation mechanism. For Al3Ti/6070Al composites, the optimal ultrasonic power is 1.6 kW, and the best reaction time is 3 min; The Al3Ti particles size is reduced from 2-5μm to about 1μm, and the morphology becomes smaller and granular; For Al2O3/Al composites, the optimal ultrasonic power and reaction time are 0.60 kW,2 min, respectively; The Al2O3 recoveries of the composites can be significantly improved under ultrasonic field. The preparation of TiB2/7055Al composite process mechanism was studied by water quenching. The whole reaction process can be divided into four stages, and the second stage of the reaction process under the ultrasonic field has played a significant role in reaction promoting. TiB2 particles gradually refined with the increase of ultrasonic power. Especially, when the ultrasonic power reaches 1.6 kW, a large number of nano-scale TiB2 particles are observed.The preparations of Al3Ti/6070Al, Al2O3/Al, TiB2/7055Al composites under low frequency magnetic field were studied. The results indicate that for Al3Ti/6070Al composites, two different type composites including uniform distribution and gradient distribution can be obtained with the change of excitation current and frequency. When the excitation current is 200 A, the frequency is less than 5Hz, the reaction time is 3-5 min, small sized particles and uniform distribution Al3Ti/6070Al composites can be prepared; meanwhile, gradient distribution composites can be prepared by increasing frequency or current and correspondingly reducing reaction time. Based on the above experiments, it can be conjectured that secondary flow exists in the melt while preparing composites by the continuous action mode under magnetic field. Through water quenching in the intermittent action mode, the process mechanism of TiB2/ 7055Al composites under low-frequency magnetic stirring was studied. The in situ reaction is accelerated at the early stage with assistance of magnetic filed. When the frequency is small (<5 Hz), the size of TiB2 particle size has no significant change. As long as the frequency is over 5Hz, the size of particle tends to be the same, and morphology is passivated.The Al3Ti/6070Al and TiB2/7055Al were synthesized under coupled field by using the optimized parameters from single field. The results show that the Al3Ti particles have tiny sizes and well distributed under the coupled field. To be more precisely, when the power of ultrasonic is 1.6 kW, the size of Al3Ti in range of 0.2-0.5μm is about 72.4% to total number. At the same time, nonetheless, the prercentage of particles in range of 0.8-1.2μm have a considerablely decrease to about 1.6%. The size of Al3Ti grows larger as the amount of powder addition increases. Further, morphologies of the particles are changed from small block and granular to large block, piece or short rodlike with assistance of coupled field. When TiB2/7055Al composite fabricated under the coupled field with continuously action mode, a large number of nanoscale TiB2 particles can be observed with 0.8 kW of ultrasonic. The size of inhomogeneous distribution particles is in range of 80-100 nm. While TiB2/7055Al fabricated under the coupled field with intermittently action mode, submicron scale TiB2 particles with uniformly distributed can be obtained.The mechanical properties of 7055A1 alloy show that the tensile strength and hardness are decreased with increase of yttrium addition, while elongation is increased. The tensile strength and elongation of 6070A1 are increased at first then decreased with increase of yttrium additon. The tensile strength and elongation of Al2O3/Al composites synthesized under ultrasonic field is increased and then decreased with increase of ultrasonic power and action time, and their optimal parameter are 0.6 kW,2 min, respectively. The tensile properties of Al3Ti/6070Al、TiB2/7055Al composites fabricated under coupled field are better than that single field. The decreased elongation of composites is significantly restrained by interaction of coupled field and rare earth with increase of volume fraction.更多还原