Research On Mechanism Of Preparing Semi-solid Aluminum Alloy Slurry And Forming Of Microstructure With Power Ultrasonic

Power ultrasonic vibration treatment is a new environmental technique to make semi-solid slurry in 21st century. But the regulation, condition and mechanism of the ultrasound on slurry are not very clear. Thus, the field is focused on by researchers and attracting attention from material scientists and engineers.Based on the existing ultrasonic generator, the appropriate ultrasonic frequency and the material, size and shape of the Amplitude Transformer Horn were chosen to design a set of equipment to treat semi-solid slurry. The effect regulation that the strength of power ultrasound, the started temperature and the head shape of Amplitude Transformer Horn worked on the size tinning and morphology spheroidizing of the primary phase was researched. The orthogonal test was designed to obtain the complicated influence of two parameters (the strength of the ultrasound and the started temperature) and the best combination of the two parameters.The experimental results show that with the increasing of the strength of ultrasound, the power will be stronger, the style of the crystal formation will be changed more easily, and will promote the primary phaseα-AL size tinning and morphology spheroidizing. And that the best primary phase was obtained at the 640℃among the three started temperature (620℃, 640℃and 660℃) . And that the different head shape of the Amplitude Transformer Horn will cause different wave front that will lead to the different results. And that the best tinning parameters was 1500w, 620℃, the results at the point was D=38.9um, f=0.83; the best spheriodizing parameters was 1500w, 640℃, the results at the point was D=30.5um, f=0.81.According to the experimental results, the work mechanism of the ultrasonic influence including mechanics, acoustic streaming and thermodynamics was inferred from the two sides of solidification: crystal form and crystal grow. The vigorous motion of energy supplied by the thermodynamic effect of ultrasound will increase the rate of the crystals forming; the mechanics effect of ultrasound offered the promotion that the liquid atoms move to the crystal that will also increase the rate of the crystals forming. The mechanics effect of ultrasound also changed the dendrite growth of negative temperature gradient to promote the crystal nucleus to be cellular and the final microstructure to be globular. The acoustic streaming effect of ultrasound will cause the melt flow up and down. The flow can obviously change the melt temperature field in the crystallization front, reduce the thermal boundary layer thickness, raise the temperature gradient of interface, and reduce the growth rate of interface. That will lead to the formation of small organizations. And the flow also can reduce the components boundary layer thickness, make the interface stable and organization tinning.