Inverse Identification And Simulation Application Of The Interfacial Heat Transfer Coefficient During Quenching Processes Of Aluminum Alloy

Twisting,warping and other defects often occur during quenching process of large-scaled complex aluminum profile.The accuracy and the rate of final products will be affected by the quenching distortion.With the rapid development of computer technology,numerical simulation technology becomes a powerful tool to solve the quenching distortion of aluminum profile.The interfacial heat transfer coefficient(h)directly influences the simulation accuracy.In the present study,the interfacial heat transfer coefficients during end quenching experiments were calculated by inverse heat conduction method.The influence of process parameters on h was analyzed.The inverse identified interfacial heat transfer coefficient was applied to the simulation of aluminum profile extrusion on-line quenching process.The main research results are shown as following.(1)A one-dimensional inverse heat conduction model for solving h was established.The interfacial heat fluxes and heat transfer coefficients of the end quenching experiments were obtained by using this model.The results show that the interfacial heat fluxes first increase and then decrease with the specimen surface temperatures decreasing,causing that the interfacial heat transfer coefficients also increase first and then decrease.The interfacial heat transfer coefficient of the spray quenching increases with the surface temperature decreasing for the low flux density of the medium at the specimen surface.(2)The influence of water temperature,roughness and ultrasonic stirring on h of the immersion quenching was explored.When the initial specimen temperature is equal to 95℃,h decreases with surface roughness and water temperature increasing.Ultrasonic stirring has increased the peaks of interfacial heat flux and heat transfer coefficient 6 and 10 times respectly.When the initial specimen temperature is 520℃,h first increases and then decreases with surface roughness increasing.The theoretical model for predicting the peak of interfacial heat transfer coefficient during the end quenching process without medium phase change was established.The relative error of the predicted value and the inverse calculated value is less than 13%.(3)The influence of specimen initial temperature,medium flux density on the surface and surface roughness on h of the spray quenching was explored.The increase of specimen initial temperature will improve the total heat storage of specimen and initial interfacial temperature difference,resulting in the increase of h during the transition boiling stage of water jet quenching process and the whole process of air jet quenching.The initial temperature for specimen has little influence on the nuclear boiling stage of water jet quenching.When the average size of the medium heat transfer unit is equivalent to its dimension,roughness has a significant effect on h.During the spray quenching and water jet quenching process,the density of bubble nucleation in the nuclear boiling stage decreases firstly,and then increases with roughness increasing.During the air jet quenching process,the increase of roughness causes the increase of time for gas residence in the boundary layer,leading to a decrease in h.Interfacial heat transfer coefficient increases with the increase of the medium flux density on the surface.When the medium flux density on the surface is greater than its critical value,due to the shortening of contact time,h will decrease with the increase of medium flux density on the surface.(4)The cooling efficiency of different medium during the end quenching process has been compared using the maximum heat absorption per unit volume of cooling medium.The results show that the cooling efficiency per unit volume of mist is highest,and per unit volume of air has the lowest cooling efficiency.With the increase of the medium flux,the increase of the cooling efficiency of water is biggest,followed by air,and the cooling efficiency of mist only little change.The cooling efficiency per unit volume of medium decreases with medium flux density increasing.(5)A finite element model was established.The extrusion online air quenching process of aluminum profile was simulated using the finite element model.The inverse identified interfacial heat transfer coefficient was used as a boundary condition.When the wind speed is greater than 20m/s,the average cooling rate of the profile during the temperature range of quenching sensitive is greater than the cooling rate required by 6082 aluminum alloy quenching.With the increase of the air jet speed,the stress and strain of the aluminum profile increase,leading to an increase in the probability of quenching distortion.During the temperature range of quenching sensitivity,the average relative error between the calculated temperature and the measured temperature is about 8.5%,which indicates that the inverse identificated interfacial heat transfer coefficient has a high accuracy.