Effect Of Mechanical Vibration On Microstructure And Mechanical Properties Of Vacuum Counter-Pressure Casting ZL114A Alloy

As an Al-Si alloy material with low density,high strength,high stiffness,good casting properties,ZL114 A alloy is widely used in aviation,aerospace,national defense and other fields.The alloy undergoes eutectic transformation during the casting process,and the eutectic silicon structure often precipitates in needle or flake shape,which is easy to cause stress concentration and lead to unexpected failure.In this paper,the relative density,hardness,tensile strength,elongation of the sample are systematically measured by applying mechanical vibration in the vacuum counter-pressure casting process of ZL114 A alloy.The microstructure and fracture morphology of the sample are observed and analyzed.The influence of mechanical vibration frequency and amplitude on the organizational structure evolution and mechanical properties of the alloy are studied.The main conclusions are as follows:When the frequency is 56 Hz and the amplitude is 0.24 mm,the relative density of the alloy is highest as 0.9979 than others,which is 3.45% higher than that of the sample without mechanical vibration.With the increasing frequency,the eutectic silicon structure is more likely to be broken under the effect of the turbulent resistance of the alloy melt,and the shape transformation as "needle-block-network",which is conducive to the improvement of the mechanical strength of the alloy.When the frequency is 80 Hz and the amplitude is 0.12 mm,the maximum tensile strength is 335.66 Mpa,but the elongation at this time is only 1.52%;because the increase in frequency promotes the precipitation of Si element,the hardness of the α-Al dendritic matrix decreases.When the frequency is80 Hz and the amplitude is 0.48 mm,the minimum microhardness is around 90 HV.At this time,there are more cleavage planes in the fracture morphology,showing a cleavage fracture morphology.However,under the condition of increasing the amplitude,because the frictional resistance of the profile wall is dominant,the density of the sample is reduced,and the effect of the amplitude on the equiaxation and refinement of the crystal grains is more obvious.The average diameter of the crystal grains decreases according to the amplitude,which is 44.89,42.43,30.50,28.61μm respectively,the eutectic silicon structure is broken under the action of the excitation force.The microhardness increases first with the increase of the amplitude,when the vibration parameter is 28 Hz,0.06 mm the highest value is 127HV;the elongation rate increases with the increase of the amplitude,reaching the highest value of 4.12% under the condition of 40 Hz frequency and 0.24 mm amplitude.It can also be seen from the fracture morphology shows dimple features.Affected by the wall thickness effect,the relative density,microhardness,tensile strength and elongation of the specimen on the far-vibration source side are all lower than the strengthening effect on the near-vibration source side.Under the same parameter,the density is reduced by up to 8.34%.Part of the crystal grains exist in the form of short rods,showing quasi-cleavage fracture.This article uses mechanical vibration technology to significantly improve the microstructure and mechanical properties of vacuum counter-pressure casting ZL114 A alloy,which can provide a certain theoretical basis and technical guidance for casting aluminum alloys with good comprehensive properties.