Study On The Casting Technology Of Flexible Metal Mold And Its Solidification Microstructure And Properties

In the current study,an innovative casting method,namely flexible metal mold casting,was proposed to solve the problems of long production cycle and poor concession existed in metal mold casting process,as well as the drawbacks such as the low cooling rate and the coarse dendrites by the lost foam casting.Flexible metal mold casting is a method that the magnetic casting process with forced cooling function,that the steel shots in the sand box are forcedly air-cooled with a bottom-up manner to increase the convection heat transfer of the gap between steel shots to achieve the purpose of improving cooling rate of the flexible metal mold.Firstly,the experimental device of the flexible metal mold was designed based on theoretical calculation.Then,the microstructure and properties of cast aluminum alloy A356 and high manganese steel ZGMn13 were studied under the different process parameters.Finally,the technical scheme of the ZGMn13Cr2 large plate parts produced by flexible metal mold casting was designed.The influence factors of heat transfer mode and cooling rate of the flexible metal mold were explored by a theoretical calculations.And the results showed that the heat transfer mode of flexible metal mold was dominated by the convective heat transfer.It was discovered that there were factors of the cooling rate of the mold which were the density which of steel shots packed and output flow of blower.Meanwhile,it was supported by calculations that the cooling rate was improved with the increasing of density or output flow.Additionally,the forming system,excitation system and cooling system of the experimental device were designed based on the forming principle,basic laws in magnetism as well as the principles of convection heat transfer.The effects of current and control frequency of the blower on the microstructure of aluminum alloy A356 were investigated by experiments.The results showed that the current had a great influence on the morphology of ?-Al solid solution and the content of the eutectic structure.The ?-Al solid solution gradually changed from coarser dendrites to rose-like and the eutectic structure content decreased from 39%to 24%with the increasing of current.It showed a decreasing trend of improving the current and control frequency of the blower on the secondary dendrite arm spacing.When the current was improved from 2A to 6A with the frequency of 10Hz,the secondary dendrite arm spacing reached the minimum of 38.12?m.And when the frequency was improved from 10Hz to 22.5Hz with the current of 6A,the secondary dendrite arms spacing reached the minimum of 29.31um.However,there was an opposite influence trend of current and control frequency of the blower on the length and aspect ratio of eutectic silicon compared to the secondary dendrite arm spacing.When the current improved from 2 A to 6 A,the length and aspect ratio of eutectic silicon increased by a big margin to 44.56 um and 5.88,respectively.When the frequency was improved from 10 Hz to 22.5 Hz,the length and aspect ratio of the eutectic silicon all decreased to the lowest of 28.15 ?m and 4.27,respectively.The effect of control frequency of the blower on the microstructure and properties of ZGMn13 were investigated by experiments.The results showed that the as-cast microstructure of ZGMn13 consisted of austenite matrix,the reticular or massive M3C type carbides at the grain boundaries.The heat-treated microstructure of ZGMn13 consisted of austenite matrix and the granular carbides that were distributed in the grain boundaries.Meanwhile,the austenite grains were refined with the increasing of frequency.When the frequency was improved from 5Hz to 20 Hz with the current of 2A,the average grain size of as-cast and heat treatment all decreased to the lowest of 82.12?m and 96.34?m,respectively,which were 20.54%and 16.77%lower than that of without ventilation.In addition,when the frequency was improved from 5Hz to 20Hz with the current of 2A,it also showed that properties,such as the hardness,impact toughness and impact wear-resistance,were improved.The Brinell hardness of as-cast and heat treatment increased to the highest of HBW237 and HBW183,respectively,which were 9.72%and 16.39%higher than that of without ventilation.Meanwhile,impact absorption energy of heat treatment was increased to the highest of 124.82J,which meant that the impact toughness was the optimum,which was 13.49%higher than that of without ventilation.And the impact fracture characteristics were mainly dimples,which indicated that the fracture mechanism was dominated by ductile fracture.Moreover,the wear-resistance was best of 12.64×10-3(10min·mg-1),which was 18.57%higher than that of without ventilation.And the wear mechanism was dominated by abrasive wear,which manifested by the worn surface was mainly furrowed with plastic deformation,and a small number of micro-cracks were distributed near the furrow.At the same time,strength and plasticity of ZGMn13 were also improved with the increasing of control frequency of blower.At the frequency of 5Hz,the tensile strength and percentage elongation of the castings were 602 MPa and 26.75%,respectively,which were 13.4%and 28.92%higher than that of without ventilation.The ZGMn13Cr2 large lining board was taken as the object,then the forming system,cooling system and excitation system of the flexible metal mould casting were designed,and the relevant process parameters were given.Moreover,the molding principle of flexible metal mold was drawn.Additionally,the rationality of process parameters and structural design were verified by ProCAST,which can provide a reference for the forming of large plates by flexible metal casting.