Fabrication And Microstructure Of In-situ Particulates Reinforced 7055 Matrix Composites Synthesized By Sonochemistry

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.