Effects Of Ultrasonic On The Microstructure Of Hypereutectic Al-Si Alloy

The hypereutectic Al-Si alloy are widely used in aviation, electronicinformation, transportation and other fields because of the property of good castingperformance, low thermal expansion and high wear resistance. However, the coarseplank primary Si is usually contained in the solidification organization ofhypereutectic Al-Si alloy under normal casting conditions. Effective refiningmeasures are necessary due to the coarse plank primary Si can significantly reducethe processing performance and mechanical properties. Treating by high energyultrasonic is a new melt processing technology. Under high-intensity ultrasonictreatment, better alloy solidification organization are obtained, grain size aredecrease and microstructure uniformity are improved, in the meanwhile, gas andimpurities in the alloy melt are removed. The refining effects and laws ofhigh-intensity ultrasonic refinement on the microstructure of Al-20%Si wereinvestigated.Firstly, the influence laws of microstructure of Al-20%Si treated byhigh-intensity ultrasonic with different process parameters were researched. Theeffects of alloy microstructure treated by ultrasonic with different output power(400~1000W) and different duty cycle (0.5~1.0) were studied in the case of settingup the melt temperature as680degrees Celsius and the process time as100seconds.The results show that the coarse plank primary Si in Al-20%Si is gradually refinedand well-distributed, and its shape is changed to be spherical granules as well withthe high-intensity ultrasonic output power improving. The refined effect is reducedwhen duty cycle decreased. Finer refining effect could be gained using continuousultrasonic treatment than ultrasonic pulse structure treatment.Secondly, the influence laws of microstructure of Al-20%Si treated byhigh-intensity ultrasonic with different sonophoresis positions were researched.The results show that the best microstructure would be obtained when theultrasonic import position was under the melt surface with10millimeter depth inthe center. The refined effects of microstructure were deteriorated and the refinedareas in solidification organization were reduced with the depth of the ultrasonicimport position increased. The similar situations were appeared with the distanceincreased between the ultrasonic import position and the centre of the melt.Finally, the effects of microstructure of Al-20%Si treated by high-intensityultrasonic with the ultrasonic horn in different movement pattern ways were researched. The results show that the best microstructure would be obtained only inthe area close to the movement path of the ultrasonic horn when the ultrasonicimport position was moved along the radial of the crucible in reciprocating way.The uniformity of the macroscopic solidification organization was poor and thediversity of the grain size in different regions of the organization was large. Therefinement area could be achieved maximum, the primary silicon is refined andwell-distributed and also its shape is changed to be roundness when move theultrasonic stem at the circle with1/2of ingot casting radius to the center of melt ata constant speed.