Research On Pseudo Hot Isostatic Pressing Process Of Spray Forming Composite Sheet Under Gradient Temperature Field

Gradient composite material is a new type of composite material with continuous changes in internal composition,structure and performance.It can well meet the demanding conditions of different technical requirements for different positions of the material,and has been widely used in various fields.The dual-station spray composite deposition atomization technology is a new type of spray forming technology,which can realize the one-step spray forming of bimetallic gradient composites.Compared with other traditional casting and powder metallurgy methods,the gradient composite materials prepared by using spray forming technology have many advantages,but the initial material of spray forming contains a small amount of pores,and a subsequent densification process must be carried out to obtain Good comprehensive mechanical properties.Compared with conventional processes such as hot extrusion,forging,rolling,and hot isostatic pressing,Pseudo Hot Isostatic Pressing process(Pseudo-HIP)is simple to operate,low in cost,and has a good densification effect.It is also of great significance for large-scale industrial production.However,for gradient materials,due to the gradient changes in their composition,composition,and properties,there will be problems such as uneven densification under traditional methods for thermal processing and densification.In this paper,in order to solve the problem of uneven densification and deformation of gradient materials,the traditional Pseudo-HIP is improved,and the blank is heated or cooled in one direction through two spacers placed on the upper and lower surfaces of the blank.,In order to form a gradient temperature field in the blank,at the same time the spacer block makes the blank subjected to greater shear stress during the densification process,so that the blank is more likely to be densified.The 7075/Al-20 Si gradient composite material alloy prepared by dual-station spray forming equipment is used as the research object to study the quasi-HIP densification of porous gradient materials.The ABAQUS software was used to simulate the heating process of the blank.The results show that when the blank is heated by the spacer,the heating power,the material of the heating block and the cooling block,the size of the blank itself,and the interface heat transfer coefficient between the spacer and the blank will all affect the heating speed and the blank.The gradient temperature field affects;under the condition that the heating power is 150 W,the blank diameter is 40 mm,the heating block is a brass block,the cooling block is a steel block,and the interface heat transfer coefficient between the cushion block and the blank is 10,the blank The maximum temperature difference is11.3?,and the billet heating has a large speed,which can well meet the requirements of the densification experiment.The thermal simulation experiment of spray-deposited 7075/Al-20 Si gradient composite plate materials was carried out on the Gleeble-3500 thermal simulation test machine.The true stress-strain curve was drawn and the constitutive model of each layer material was obtained by fitting.The ABAQUS software was used to simulate the Pseudo-HIP densification process of the blank under the gradient temperature field.The simulation results show that when the temperature gradient is small,the high silicon part of the upper layer of the blank has a larger deformation and a higher degree of densification;when the temperature gradient is larger,the lower silicon part of the blank has a large amount of deformation and a higher degree of densification;The maximum temperature difference on the blank is between 15 ? and 20 ?,and the density distribution of the blank after Pseudo-HIP is more uniform.The existence of the spacer block will affect the deformation of the blank,and the deformed shape of the blank will be changed from a slightly concave shape to a drum shape;the spacer block can increase the shear stress of the blank,so that the blank can achieve better under the same pressure.High density;under the heating conditions in this article,the existence of the spacer can also improve the density distribution of the blank after pressing.Within a certain range,the higher the block height,the lower the powder height,the higher the temperature,and the higher the pressure,the higher the compactness of the blank and the greater the degree of deformation.According to the simulation results,a temperature collection experiment was carried out to verify the results of the temperature field simulation.The results show that different pad material,blank size and interface contact conditions will affect the heating rate and temperature field distribution.When a copper block is used as the heating block and a steel block is used as the cooling block,a better gradient temperature field can be obtained.According to the simulation results,a Pseudo-HIP densification experiment was carried out to analyze the deformation of the parts after pressing under different conditions,and to measure the relative density of each layer.The results show that the relative density distribution of the blank obtained by densification under a gradient temperature field is very uniform,while the relative density distribution of the blank obtained by densification and deformation under a constant temperature field is not uniform;as the applied pressure increases,the blank The density is improved.Under 120 MPa pressure,the relative density of the pressed parts reaches about 0.985,which basically achieves complete densification.The microstructure and Vickers hardness of the pressed part and the initial blank are analyzed by the hot isostatic pressing densification experiment.The results show that there are a large number of pores in the microstructure of the initial blank.After the densification experiment,the blank The pores on the parts have basically disappeared,and the silicon phase distribution is more uniform;the Vickers hardness distribution on the initial blank is uneven.After the densification experiment,the Vickers hardness distribution is uniform,and the Vickers hardness value can be increased when the degree of densification is high.