Study On Effect Of Mechanical Vibration On A356Aluminum Filling And Solidification

The objective of this paper is to investigate the influence of vibration frequency aswell as the amplitude and the orientations on the filling and solidification processes ofA356aluminum alloy during its gravity die casting process. The vibration exerted onthe metal was chosen to be mechanical vibration with low frequency.The influence of vibration frequency and amplitude and vibration direction on thecharacteristic of A356aluminum alloy, including the fluidity of metal, shrinkageporosity, pinhole, grain size and the mechanical characteristic, was investigated basedon filling and solidification experiment with vibration experimental equipment.Conclusions could be drawn as follows:①In the case of vertical vibrating at amplitude of0.9mm, the fluidity of alloy wasthe best when the vibration frequency increased to15Hz. In the case of verticalvibration at vibration frequency of50Hz, the fluidity of alloy was the best when thevibration amplitude reached to0.3mm. In tandem to that maximum, the fluidity of alloydecreased with the vibration frequency and amplitude increase. In the case of vibratingat vibration frequency of50Hz and amplitude of0.9mm, vertical vibration (vibrationdirection angle of90°) was helpful to improve the fluidity of alloy, and the fluiditylowered with the direction angle decreasing.②Vibration could put off the channel closed time because of breaking dendriteand expanding feeding channel, so the alloy liquid feeding speed and feeding efficiencyimproved with the vibration frequency or amplitude increasing, whitch led to shrinkageporosity of the sample relieving. Moreover, the increasing of direction angle ofvibration could also relieve the shrinkage porosity of the sample.③The speed of small bubbles gathering and growing and rising increased due tothe vibration frequency or amplitude or vibration direction angle increasing. Thepinhole was also released and moved gradually to the riser zone.④The grain was fined because of the increase of vibration frequency andamplitude, which resulted in better strength and elongation. With vertical vibrating, themaximum of elongation and strength were achieved when the amplitude was0.9mmand frequency of vibration is30Hz. The elongation and strength reduced with theincrease of vibration frequency and amplitude after the maximum. When vibrating atfrequency of50Hz and amplitude0.9mm, the increase of direction angle of vibration contributed to the fining grain. However, the elongation and strength still reduced.The effects of vibration on the fluidity and the feeding ability of molten metal,escape of the air from metal and the grain refining was studied. It was revealed that thefluidity of the metal increased along with the enlargement of the vibration frequency oramplitude. Moreover, the average velocity of feeding was improved by larger vibrationfrequency or amplitude. The broken of the dendritic crystal, which caused the expansionof the feeding channels and the delay of the closure time, could lead to better feedingability of molten metal under the field of vibration. Furthermore, the enlargement of thevibration frequency or amplitude could also promote the crashing and gatheringbetween the small bubbles and the inclusions, speeding up the formation and theescaping of bubbles and inclusions. The maximum stress of second dendritic crystal wasas well increased, which contributed to the broken of dendritic crystal and the refiningof the grains.However, the fluidity of liquid metal and strength and elongation ofsolifacation metal reduced because the vibration frequency or amplitude is too high,leading to the degree of fluid turbulence and additional flow resistance increasing andholes of solidified structure emerging.Based on the theoretical analysis and the experiment results, conclusion could bedrawn that the vertical vibration contributed the most to the process of filling andsolidification. The optimal values of vibration frequency and amplitude chosen forfilling process was10Hz to20Hz and0.3mm to0.6mm, respectively, while forsolidification process was50Hz and0.3mm.