High Temperature Forming Technology And Equipment For Lightweight Structure Of Ti-22Al-24Nb-0.5Mo Alloy

Supersonic/hypersonic flights put forward higher requirements for the carrying efficiency,heat resistance and integration of structural functions.Ti Al based intermetallics represented by Ti2 Al Nb are one of the new heat-resistant lightweight high-performance materials most likely to replace superalloys,and the demand for engineering applications is very strong.At present,most hollow multi-layer structures are manufactured using a combined forming/connection process,which is an important technical way to achieve structural weight reduction and structural function integration at the same time.This topic comes from the "high-grade CNC machine tools and basic manufacturing equipment" science and technology major special "high Mach number aircraft complex components ultra-high temperature forming equipment and key technology" project(No.2014ZX04001-141),the development of three-state station hot-forming machine and the maximum operating temperature of1200 ?superplastic forming machine,The high temperature deformation ability and typical connection performance of Ti-22Al-24Nb-0.5Mo alloy sheet,which can be used at temperatures above 650 ?,are studied,and the typical multi-layer structure design method and preparation feasibility verification of Ti-22Al-24Nb-0.5Mo alloy are formed.Three thermal station hot-forming machines and superplastic forming machines with a maximum operating temperature of 1200 ? have been developed.Three-state station thermal forming machine preferably heat-resistant steel ZG40Cr25Ni20Si2 manufacturing heating platform,there are 2 removable lower platform,can be achieved in the "pre-heating-slow cooling" 3 hot-state stations on demand transfer,to meet the maximum operating temperature of 1000?.The ultra-high temperature superplastic forming machine uses a new silicon wire stone ceramic manufacturing heating platform,uses the "resistor wire and electrode plate and cable" power supply heating method,forms an autonomous controllable "gas-liquid composite" follow-up loading control system,the first international realization of the maximum use temperature in the air atmosphere 1200 ? index.Using in-furnace heat treatment and pulse current heat treatment to study the evolution of T-22Al-24Nb-0.5Mo alloy tissue performance,it is found that the pulse current reduces the phase transition temperature,accelerates the B2 phase transformation,and in a very short period of time,reduces the thermodynamic base of the shaped nuclear,and increases the atomic diffusion.At lower temperatures and higher strain rates,currents can accelerate dynamic recrystallization.Current can induce the evolution of weaving,eliminate the original rolling weaving structure,and form microstructures with different orientations.When the current heat treatment condition is 1050 ?/1min,Ti-22Al-24Nb-0.5Mo alloy sheet superplastic tension performance is best,the elongation rate can reach 224.6%,because the processing sample organization contains a large number of subcrystalline tissue,in high temperature deformation of the initial B2 and ?2 phases into O phase,and dynamic recrystallization occurred at the same time,showing fine-grained superplasticity.With the extension of current heat treatment time,the number of holes at the fracture is getting less and less,and the volume fraction and size of the break hole change slightly with the increase of current heat treatment time,which is the quasicleavage/dimple mixed fracture mode.Eight kinds of hollow structures are designed.Under the same weight,boundary constraints and pressure,the bearing capacity analysis is carried out,and the bearing capacity of the herringbone stiffener structure is the highest.When the distance and width of two adjacent stiffeners are the same,the higher the stiffener is,the stronger the bearing capacity is.The superplastic forming process of the double layers structure was analyzed.The die was attached at the root fillet first,then at the cross rib protrusion,at the T-shaped rib protrusion,and finally at the rib protrusion;With the decrease of strain rate,the minimum value of stiffener wall thickness increases.The results show that the surface of the ceramic die is better than that of the metal die when the forming temperature is 950 ? ? 980 ? and the maximum pressure is 3Mpa.Through the analysis of T-22Al-24Nb-0.5Mo alloy three-layers waveform strengthening structure superplastic forming process FEM simulation,the influence of various factors on forming quality and the main relationship are studied,the thickness ratio is smaller than the depth of the groove means the better forming quality,the smaller the angle,the smaller the groove depth means the better forming quality,the wider the depth of the weld groove means the better the forming quality;As the back corner of the shape when the thickness ratio of the core plate is certain and the value of meeting the accuracy requirements is reached,the height of the groove under different core plate thickness conditions increases gradually with the decrease of the core plate thickness,but can meet the accuracy requirements;Using the selected loading curve to form the three-layers structure parts,the total forming time is extended,the maximum pressure increases,the holding time increases,and the final forming part surface is smooth,no grooves and other defects appear,the forming quality is good.Preferably the laser welding penetration process parameters meet the needs of superplastic forming,no significant changes in the welding joints after forming,proving that laser welding can partially replace diffusion connections,and shorten the thermal cycle of workpieces,improve the inspection of connection quality.Three typical structural design forms of four layers lightweight structure are established,and the FEA method is used to analyze the feasibility of integral forming of three kinds of four layers structures and the formation and control of process defects,and the typical four layers structure is trial produced.Compared with the traditional four layers structure with dense grid,the thinning rate of the sheet is smaller,and the diffusion bonding process and superplastic forming process can be carried out separately;The vertical core support reinforced four layers structure can make the vertical rib only bend when designing the core plate size,which solves the problem of thinning in the forming process;After the forming of the X-shaped core four layer structure,the value of the diffusion bonding area with the core is obviously lower than that of the superplastic forming area,which indicates that there are grooves or the trend of grooves is larger.The smaller the width of diffusion bonding area between panel and core,the greater the risk of grooves.In order to prevent grooves in the diffusion bonding area between the panel and the core,the width of the diffusion bonding area should be widened appropriately;When the vertical core four layers structure is formed,one end of the diffusion connection area between the core and the panel will be bent.Because the metal outside the neutral layer is subject to tensile stress during bending deformation,and the core layer here has been diffusely connected with the panel as a whole,the core layer is depressed under the effect of tensile stress,and finally a groove is formed.