Research Of Process Mechanism And Microstructure Evolution On Ultrasonic Assisted Semisolid Friction Stir Processing

Grain refinement is commonly used in metal materials to strengthen one of the means,but also the only way to simultaneously improve the strength and ductility of the method.Friction stir processing (FSP) is an emerging severe plastic deformation of the materialprocessing method has been successfully using this technique to refine the grain size to themicron level, but the mere existence of the use of FSP further refined grains difficult.Therefore, a composite process methods of ultrasonic assisted semi-solid friction stirprocessing (UASFSP) was proposed in this paper, and its process mechanism was studied.ZL101aluminum alloy was adopted as research material in this paper. And ANSYS wasused to simulate UASFSP, which the optimal vibration frequency ultrasonic24000-25500Hzwas found, the best location for vibration: when vibration source position can be adjusted,nugget area should be located at the edge of vibration a source; when the vibration sourcelocation can’t be moved, position B can be used as a constant vibration source location whichlocated in intermediate of weld seam.Temperature measuring experiment was used to located the processing parameters ofSFSP, which was found that when n was2000r/min and the processing speed v=5mm/min,v=10mm/min, v=15mm/min respectively the weld nugget zone may reach half solid state,which the semi-solid temperature range of time is73s,32s,20s. The effects of water-coolingfor SFSP was studied, which was found that when the experimental parameters was n=2000r/min v=5mm/min, the cooled SFSP sample’s transition area between shoulder affectedzone and weld nugget is more gentle compared to ordinary SFSP sample, in which grain sizechanges lower relatively, and nugget zone grain relative refinement. By hardness test of asample of the water-cooled SFSP, it is found that the hardness of the processing region wasless than the base metal. But the hardness change width of weld nugget is significantlysmaller than the base metal. There were some processing defects was found in processingregion. Cavitation law and best vibration source location were studied by polystyrene particles-water and sediment shaped vibrating physical model experiments. Which was found that theaffect scope and intensity of cavitation ultrasonic cavitation effect was increased as therotational speed of the magnetic stirrer increased, and was debased with increased ofconcentration of polystyrene particles. It is found that the position of vibration source shouldlocated on the edge of the center position of the test plate in the sand shaped vibratingexperiment.On the basis of the aforementioned studies, UASFSP experiments was carried out.Process parameters was n=2000r/min, v=5mm/min, load power of the vibration sourcewas1000W,1400W,1800W respectively, strong cold water simultaneously. It is found thatwhen the ultrasonic power is1000W, ultrasonic machining area exists spoiler area, the extentof grain refinement in ultrasonic spoiler area is stronger than the weld nugget, hardness ofultrasonic spoiler area is no change compared to ordinary SFSP. As ultrasound powerincreased, nugget zone and ultrasound spoiler zone was fused, weld nugget area increased, thedegree of grain refinement nugget zone increased, processing defects disappeared, thehardness of the weld nugget zone increased.