Study On Heat Transfer Mechanism And Experimental Verification Of Rapid Cooling Process Of Titanium Alloy Sheet

Titanium alloy sheet is a new lightweight structural material in the fields of aerospace,marine engineering,chemical industry and nuclear industry with low density,high specific strength,excellent high temperature and low temperature performance and good corrosion resistance.Heat treatment is a key process to eliminate stress in the sheet and improve the rigidity and microstructure.Due to the small thermal conductivity of the titanium alloy,the temperature difference between the core and the surface of the cooling process is large,and the residual stress after cooling is large,which is prone to deformation and uneven thickness.In this paper,TC4(Ti-6Al-4V)titanium alloy was used as the research object to study the temperature drop law of solid solution quenching of high temperature plates under different impact jet modes,and the influence of process parameters on surface heat flux density and core cooling rate,and the optimal cooling parameters are obtained.Relevant research enriches the theory of heat transfer and heat conduction of metal sheets under ultra-fast cooling conditions,and this research grasps the influence of cooling process parameters on the surface and thickness heat transfer of titanium alloy sheets,which provides theoretical and technical support for the optimization of rapid cooling(solution quenching)process and equipment of titanium alloy sheets.The main work and results of this paper are as follows:(1)Based on the research progress of domestic and international impact jet technology,the boiling heat transfer mechanism of high temperature metal sheet surface is described,including single forced convection heat transfer,nuclear boiling heat transfer,transition boiling heat transfer and film boiling heat transfer.Based on this,the fluid structure characteristics of the jet impinging on the high temperature wall are analyzed.(2)The real-time temperature of solid solution quenching of titanium alloy sheet was collected by multi-channel temperature recorder and combined cooling experimental device.The temperature drop curve of solid solution quenching of typical hightemperature titanium alloy sheet was drawn.The surface was calculated by anti-heat transfer model and MATLAB software.The heat flux density and the cooling rate of the core are summarized,and the temperature drop law and heat transfer law of solid solution quenching of titanium alloy sheet under different process parameters are summarized.(3)Based on the self-made single-beam jet experimental device,the basic heat transfer characteristics and main influencing factors of single-beam impinging jet were studied.The experimental data of peak heat transfer density,rising velocity of heat flow density,distribution of heat transfer area,wetting speed and cooling speed in the core were obtained.The experimental data of speed and other factors analyzed the effects of process parameters such as jet velocity,jet height,tilt angle and open cooling temperature on the surface and core cooling rate of high temperature titanium alloy sheets.The results show that the increase of jet velocity and cooling temperature within the allowable range is beneficial to the increase of plate core cooling speed,and the increase of inclination angle is unfavorable to the increase of plate core cooling speed,while the change of jet distance has no obvious effect on heat transfer between the core and surface.(4)Using the laboratory array jet experimental device,the surface heat transfer characteristics of high temperature titanium alloy plate under multi-beam jet impact conditions were studied.The effects of flow rate,roll speed and cooling mode on the temperature drop of solid solution quenching of titanium alloy sheets were analyzed.Under the conditions of different process parameters,the influence of heat flux density,thickness gradient and section cooling velocity on the surface of titanium alloy plate.The results show that increasing the jet flow rate is beneficial to the heat flow density on the surface of the plate and the effect on the cooling rate of the core is not obvious.The change of the roll speed has no obvious effect on the heat transfer of the core and surface of the titanium alloy plate.