Influence Of High-intensity Ultrasonic Treatment On Microstructures And Properties Of Hypereutectic Al-Si Alloy

Hypereutectic Al-Si alloy are used in many application areas such as mechanism, automotive and aviation due to their good wear resistance and low thermal expansion coefficient. In order to improve the properties of hypereutectic Al-Si Alloy, people have examined a number of metallurgical and physical methods.The injection of ultrasonic vibration into molten metals brings about effective effects,such as cavitation, acoustic streaming,emulsification,and radiation pressure. Ultrasonic vibration of solidifying melt can refines the metal solidification structure,improving the metal properties.Firstly, the morphology and distribution of the microstructures of Al-20%Si alloy treated by high-intensity ultrasonic were studied systematically. When the ultrasonic treatment starting temperature ranges between 620℃and 680℃,effects of ultrasonic treatment starting temperature, duration and power of ultrasonic treatment on Al-20%Si alloy have been researched . The results indicate that finer primary phase can be obtained at about 660℃treatment starting temperature,longer and more powerful ultrasonic treatment. Coarse primary Si phase becomes spheric granules, spherical degree is increased, and primary Si phase is well-distributed.Secondly, in order to improve the Al-20% Si alloy finer primary and mechanical properties, Al-20%Si alloys were modificated useing PCl5 and Al-10%Re, and the modified Al-20%Si alloys were treated by high-intensity ultrasonic wave. From these, the effect of high-intensity ultrasonic on the morphology of modified Al-20%Si alloys were studied. The experimental results show that PCl5 is able to refine primary silicon of Al-20%Si alloy, but can not refine eutectic silicon refinement.However, Al-10%Re alloy can not only refine the primary silicon, but also refine the eutectic silicon of the alloy. The primary silicon of Al-20%Si alloy can be broken by ultrasonic treatment.Finally, the influence of ultrasonic treatment and modification on mechanical properties of hypereutectic Al–20%Si alloy was studied. The alloy fracture morphology observed by SEM to study the fracture mechanism of the alloy. The results show that tensile strength and elongation of Al-20%Si alloy treated by high-intensity ultrasonic are improved. The tensile fracture surface of alloy was observed by SEM. After ultrasonic treatment, many tearing slits and dimples could be observed on the fracture surface. The tensile fracture of the alloy shows characteristic of brittle fracture in combination with toughness fracture.