Study On Effect Of Mechanical Vibration On AZ91Magnesium Filling And Solidification

With the widely application of magnesium alloy on industrial production, the studyof magnesium alloy is also increasing. Due to the filling and solidification process ofmagnesium alloy directly affects the performance of magnesium alloy, the subject usedthe AZ91magnesium alloy as research object, applying low frequency mechanicalvibration force field to the process of filling and solidification, The effects ofmechanical vibration at different frequency of0hz and20Hz,35Hz,50Hz on the AZ91magnesium alloy filling and solidification process was investigated.The experimentalresults show that:①With the increase of vibration frequency, the average length of spiral sampleincreases, the fluidity is also enhanced, the average lengths of the spiral casting undervibration frequency of50Hz is increased probably14%compared to that under no existvibration.The results shows that mechanical vibration can obviously improve fillingablity of AZ91magnesium alloy.②With the increase of vibration frequency, the grain structure of magnesium alloyget refining, the inclusion content of internal continuously reduce.③After applying vibration, the maximum temperature of metal mold is rising, therequired time is falling, when vibration frequency is50Hz maximum temperature issupreme and the required time is the least under vibration frequency of50Hz, With theincrease of vibration frequency, the heat transfer efficiency of the interface betweenmold and casting is improving.④From the range of0to35Hz, with the increase of vibration frequency, theporosity of sample is decreasing compared to that under no exist vibration, when thefrequency reached the maximum50Hz, the porosity ratio increases to6.57%, it isgreater than when not apply vibration.This article also researched on the mechanism what the mechanical vibrationinfluence on the AZ91magnesium alloy include filling ability, grain size, inclusioncontent, the heat transfer efficiency of the interface between mold and casting, porosity.The research results show that:①T heapplication of mechanical vibration on the process of filling andsolidification of magnesium alloy can break dendrites, speed up the velocity ofinclusion floatation, and reduced the content of inclusions in the castings, slowing the tendency of a gradual increase in the viscosity of molten metal increase, reducing thefrictional drag. thereby increase the filling ability of magnesium alloy.②T hemechanical vibration can make the molten metal contact closerly with themold wall, the thickness of Laminar boundary layer between the mold and molten metalis reduced, the contact gap get smaller, the contact area is increasing, the convectiveheat transfer coefficient also improve, of course, the heat transfer efficiency of interfacenaturally increase.③when the mechanical vibration frequency kept in a certain range, the mechanicalvibration can promote the bubble grew up, collision, merger in the liquid metal, increasethe floating speed, decrease the porosity in the castings. And too much vibrationfrequency can accelerate the velocity of bubble is rising, but too stronger mechanicalvibration can absorb more and more gas into molten metal. In addition, big vibrationfrequency boost the velocity of solidification, many bubble can not escape from themolten metal in the shorter time before the casting completely solidification, The factorswould increase the porosity in the castings.