Study On Mechanism And Technology About Power Ultrasonic Refinement For Solidification Structure Of Magnesium Alloys

Magnesium alloys are increasingly applied into the automotive, electronics and communication industries due to their low density high, strength-to-weigh, rigidity-to-weigh ratio, good damping capacity and good electromagnetic shielding properties. However, the key problem to extend the wide application magnesium alloy is to improving deforming ability.Many practices proved that the fine equiaxed crystals structure magnesium alloys could improve mechanical properties. It is very important to find an effective grain refinement for magnesium alloys. Ultrasonic treatment is an efficient and non-contaminative metal refining technique. However, few research on the grain fining of magnesium alloys with ultrasonic in solidification process was done before. Therefore, it needs urgently to carry out a deep-going investigation in this region, which includes discussing the mechanisms of grain fining of magnesium alloys with ultrasonic and the technological parameter. In this paper, the solidification process of AZ31B and AZ91D magnesium alloys was processed by power ultrasonic, and the mechanism and technology of power ultrasonic refinement was widely investigated.Firstly, the method of ultrasound physical modeling experiments was used to study on effects of various factors, such as acoustic streaming, ultrasonic cavitation , on ultrasonic refinement process. And the glycerol, methylene blue solution and ammonium chloride are selected as physical simulation medium of ultrasonic treatment The experimental results show that the effective range of the acoustic stream is different while the ultrasonic power, the medium temperature, the ultrasonic treatment time and the location of ultrasonic amplitude amplifier pole are changed. And the intensity of ultrasonic cavitation is different with changing ultrasonic power, ultrasonic treatment time and distance of ultrasonic amplitude amplifier pole. Also the crystallization of ammonium chloride is different with changing ultrasonic power, ultrasonic treatment time and the concentration of ammonium chloride.Secondly, sound power was measured by calorimetry and efficiency of transducer was calculated. In order to probe into the solidification mechanism of AZ31B and AZ91D magnesium alloys when power ultrasonic was directed into the molten melt, the cooling curves of AZ31B and AZ91D magnesium alloys under 0W, 200W, 400W, 600W and 800W ultrasonic power were measured. The research results showed that the solidifying beginning and end temperature were improved. Furthermore, the solidification time become shorter and the cooling rate of solidification become faster.Thirdly, the effects of processing parameters such as the temperature range, ultrasonic power, attenuation and the cooling mode of ultrasonic treatment on ultrasonic refinement process were researched by introducing power ultrasonic into the solidification process of AZ31B and AZ91D magnesium alloys .The experimental results showed that with continuous treatment, 600w ultrasonic power and water-cooling mode, the finest refining effect on magnesium alloy could be achieved. The ultrasonic attenuation exists along the ultrasonic propagation in the molten metals .And the range of ultrasonic refinement was limited.Lastly, the rolling deforming tests prove that the deforming properties of AZ31B alloy after ultrasonic treatment was enhanced significantly.