【作者】 陈登斌；

【导师】 赵玉涛；

【作者基本信息】 江苏大学 ， 材料加工工程， 2009， 硕士

【摘要】 7055合金是航空航天领域的重要材料,近年来随着航空航天工业的飞速发展,对该材料的综合性能提出了更高的要求,进一步改性或强化7055合金已成为当前发展大飞机用材料的研究热点和重点之一。本课题通过稀土合金化和原位颗粒强化联合方法进一步提高7055合金的综合性能。探索了稀土合金化对7055铸态微结构的影响;研究了高能超声作用下7055Al-K₂TiF₆体系合成Al₃Ti颗粒增强7055基复合材料以及7055Al-K₂TiF₆-KBF₄体系合成TiB₂颗粒增强7055基复合材料的微结构和机制,并采用X-射线衍射仪（XRD）、扫描电镜（SEM）、能谱仪（EDS）等现代分析和测试方法,分析了稀土合金化和原位颗粒增强7055基复合材料的微观组织、相组成以及内生颗粒的形貌、大小、分布特征。获得的研究结果如下:1.在7055铝合金中添加单一稀土Y后铸态组织得到明显的细化,当Y加入量0.25wt.%时晶粒细化至20-30μm,并使原来骨骼状的第二相细化,局部出现球化,但当Y过量（>0.25wt.%）出现粗化,形成Al₆Cu₆Y相,并呈块状或条状分布于晶界;添加复合稀土（0.15wt.%Y+0.1wt.%Ce）时,晶粒进一步细化至15-20μm,晶界呈半连续分布,且较0.25wt.%Y时更为清晰、细小,共晶相尺寸显著细化,球化的第二相增多。2.高能超声作用下7055Al-K₂TiF₆体系原位生成的增强颗粒为Al₃Ti,颗粒尺寸在0.5-1.0μm之间,主要为短棒状或小块状,部分为粒状。添加单一稀土Y时,Al₃Ti在凝固过程析出的部分得到细化,使复合材料增强颗粒趋向均匀:当添加复合稀土0.15wt.%Y+0.1wt.%Ce时,增强相颗粒进一步细化。复合材料的重熔结果表明,随重熔保温时间及重熔次数的增加,Al₃Ti迅速长大,且当重熔次数达到2次时颗粒数量明显减少。一定超声强度下（0.66kW/cm²）,在1-7min范围内,随着超声作用时间的增加,内生颗粒的数量先增大后减小,尺寸先减小后增大,较佳作用时间为3min左右,此时内生颗粒最为细小,体积分数最高。对于7055Al-K₂TiF₆体系,在一定作用时间下（3min）,随着超声作用强度的增大,复合材料中的内生Al₃Ti增强颗粒尺寸显著减小,数量也随之减少。3.高能超声作用下7055Al-K₂TiF₆-KBF₄体系原位生成的增强颗粒为TiB₂,尺寸在80-100nm之间,呈六棱粒状,部分颗粒出现“球化”现象。水淬试样的SEM和EDS结果表明,高能超声能显著地促进7055Al-K₂TiF₆-KBF₄体系的原位化学反应的进程,缩短化学反应的时间。探讨了高能超声作用下熔体反应法制备内生颗粒增强铝基复合材料的动力学及反应机制,认为主要是超声处理熔体时产生的声空化效应、声流效应、机械效应和热效应的综合作用。更多还原

【Abstract】 7055 aluminum alloy is an important construction material, which is widly used in the fields of aerospace, automobiles and so on. With the development of economic the demands for properties of matericals are enhanced, such as stengenth at room and high temperature, fracture toughness and fatigue life et al. In the paper rare earth alloying and introducing endogenous particles in matrix were utilized in the fabricatioin of modified 7055.The aims are to optimize the structure and enhance the service performance of new materials.The paper is composed of three parts:（1） The effects of rere earth elements on the microstructure of as-cast 7055;（2）In situ Al₃Ti particulates reinfoeced 7055 composites using 7055Al-K₂TiF₆ components by sonochemistry;. （3） In situ TiB₂ particulates reinfoeced 7055 composites using 7055Al-K₂TiF₆-KBF₄ components by sonochemistry. The solidification microstructure, patterns of in-situ particulate, composition of phase were investigated with the help of Optical Microscope （OM）, Scanning Electron Microscope （SEM）, X-ray diffraction （XRD） and other modern equipments.The results show that the microtructure of 7055 alloy is refined with trace yttrium addition and the second phases are granulated, sphercized and fined. The blocky or stripy Al₆Cu₆Y phases can be observed on the boundries when the yttrium content is up to 0.25wt.%. When adding 0.15wt%.Y+0.10wt.%Ce the grian size ofα-Al and second phases are further refined, meanwhile the semi-continuous grain boundaries are finer. Moreover, the amounts of spheroidized phases are increased remarkably and eutectic phases are refined greatly.The particles synthesized under high intensity ultrasonic field in 7055Al-K₂TiF₆ are Al₃Ti, whose sizes are 0.5-1.5μm. The morphology of Al₃Ti exhibits as short beams, small block and granular. Al₃Ti particulates are refined and the sizes trend to uniform with 0.25wt.%Y addition.The particles tend to be further refined with 0.15wt.%Y +0.1wt.%Ce additon. The remelting of Al₃Ti/7055Al composite shows that Al₃Ti particulates grow up rapidly with holding time and remelting times increasing.In 7055Al-K₂TiF₆ system with constant ultrasonic intensity （0.66kW/cm²） ,the sizes of Al₃Ti particles decrease firstly then increase in the range of 1-7min of ultrasonic radiation time. The smallest size and highest volume fraction are obtained when the ultrasonic radiation time is fixed at 3 minutes.When the ultrasonic radiation time is constant both the sizes of Al₃T particles and volume fraction are decreased when the ultrasonic intensity increase.TiB₂ particles are synthesized under high intensity ultrasonic field in 7055Al-K₂TiF₆-KBF₄, whose sizes are 80-100nm. The morphology of TiB₂ are six-rowed granular, parts of them are spheroidized The results indicate that the in situ chemical reactions are speeded up with the high intensity ultrasonic field introduced into the aluminum melt, and the reaction time reduced. The effects can be attributed to the cavitation effects, acoustic-streaming effects, mechanical effects and the thermal effects of the high-energy ultrasonic field.更多还原