| ZL205A aluminum alloy is a high strength casting aluminum alloy developed by our country.ZL205A aluminum alloy has a low density,high specific strength,better corrosion resistance and fracture toughness,so it is widely used in the field of aerospace engineering.Cylindrical tank shell is the key to the Mechanical structure in aerospace craft,it has vast size,complicated structure and mechanical properties of demanding strict.In this paper,ZL205A cylindrical castings are used to study the residual stress of metal casting,which is used to reduce the residual stress of castings and ensure good mechanical properties.In this paper,multi-channel temperature acquisition,drilling,X-ray diffraction,polarizing microscope,scanning electron microscopy and tensile test and other detection methods.The effects of sand thickness on casting residual stress,solidification cooling process,grain size,morphology and mechanical properties were studied.Through the numerical simulation,the temperature field,the stress field and the deformation law of the casting are studied.And the applicability of the Von Mises model and the Mohr-Coulomb model of the coated sand at different thicknesses were investigated in combination with the actual casting results,which can provide a reference for reasonable prediction of residual stress in iron sand casting.The main results were as follows:(1)The results show that the residual stress of castings can be reduced by about 62%,from 134.3MPa to 50.4MPa,when the sand thickness reaches 7mm.The residual stress changes a little with the sustained increasing of sand thickness.The average residual stress of the castings is reduced to 30.1 MPa when the sand thickness is increased to the total sand core.(2)The increase in sand thickness will reduce the casting cooling rate.The average solidification cooling rate of the castings is 7.59 ?/s,4.76 ?/s,3.93 ?/s,3.73 ?/s,2.01 ?/s,respectively,when the sand thickness is 0mm,4mm,7mm,10mm and the whole sand core,the grain size of the aluminum-copper alloy is 7,6,5,5 and 4 respectively.Although the residual stress reduction effect is good when the whole sand core is used to cast,the cooling rate decreases as low as 2.01 ?/s,and the grain size is coarse,grain boundary secondary phase was coarse and continuous.(3)With the increase in sand thickness,the casting capacity is improved and the secondary phase become continuous and large at the grain boundary.The use of iron sand casting to reduce casting stress,the need to consider the overall performance of castings.When the thickness of sand is 7mm,the residual stress,grain size and thermal cracking tendency of castings are small,and the mechanical properties of castings are the best.The as-cast tensile strength and elongation were the highest among the castings,which were 6.7%and 207MPa,respectively.(4)The numerical simulation results are in agreement with the actual casting conditions.Compared to the metal casting,the final setting of the iron-type sand casting casting is shifted from the center of the wall of the casting to the sand layer,reducing the tensile stress at the center of the wall thickness of the casting.With the increase of the thickness of the sand,the radial shrinkage of the castings is smaller,and the radial shrinkage increases with the symmetrical thickness.The simulation results of Von Mises model are in good agreement with the experimental trend,but the it deviates greatly when the sand thickness is 4mm.The study of the mechanical properties of different sand layers shows that the smaller the sand thickness is,the greater the compressive strength of the sand is affected by the confining pressure.Mohr-Coulomb model is added to the confining pressure to be modified,and the calculation deviation is small when the sand thickness is 4mm,but the model deviation increases with the increase of sand thickness,When the residual stress is predicted by numerical simulation method,Select the appropriate sand mechanical model is a good way to ensure a more accurate calculation of the results. |
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