Study On Temperature Field Measurement Of Aluminum Alloy Based On Infrared Radiation And Iterative Algorithm

Aluminum alloy is widely used in various fields with its excellent physical properties,and with the continuous development of aluminum alloy industry,the industrial requirements for its quality are also increasing.When using non-contact temperature measurement such as infrared thermography,the surface emissivity of aluminum alloy varies with temperature due to its own material characteristics,which makes it impossible to obtain accurate emissivity and thus causes large measurement errors.In order to reduce the influence of emissivity on the measurement accuracy in the process of using infrared thermography,and to improve the accuracy of infrared thermography measurement of aluminum alloy temperature,this paper proposes an iterative emissivity algorithm based on emissivity-temperature characteristic curve,and iteratively corrects the initial infrared temperature field by calibrating the emissivity-temperature characteristic curve of the same type of aluminum alloy sheet,and applies it to uniformly heated The algorithm is applied to the measurement of the temperature field of aluminum alloys during uniform heating and the temperature field of aluminum alloys during friction stir welding.First,the emissivity-temperature characteristic curve was measured and calibrated,and based on this,an iterative algorithm for emissivity was constructed and used in the uniform aluminum alloy temperature field measurement.The aluminum alloy plate was polished using a milling machine and measured using a surface roughness meter to ensure that the oxidation degree of the aluminum alloy plate was consistent with the roughness,after which thermocouples were buried on the side of the aluminum alloy plate and placed on a ceramic heating furnace for heating,and the thermocouple values were recorded,while infrared thermograms were recorded using an infrared camera,and the emissivity-temperature characteristic curve of this type of plate was obtained by fitting it using a rational function,and then the The emissivity iteration model was then developed based on the curve and applied to the temperature field measurement experiments of uniformly heated aluminum alloys.In the uniform heating experiment,the aluminum alloy is placed above the ceramic heating furnace to simulate the uniform heating process.The temperature error does not exceed 8 K,which meets the requirements of industrial production and improves the accuracy of infrared thermal imaging camera to measure the temperature of aluminum alloy.Second,to test the applicability of the model,it was applied to the stir friction welding experiments with more complex temperature variations.Firstly,two aluminum alloy plates fully sprayed with blackbody material were used to verify that the temperature field on both sides of the weld has a certain symmetry during the welding process,and then the aluminum alloy plates sprayed with blackbody material were welded with the untreated aluminum alloy plates,and the infrared temperature field of the untreated aluminum alloy was compared with the blackbody temperature field after iterative correction by the model,and the experimental results showed that the maximum absolute temperature error was 6.67 K.The model can realize the dynamic real-time accurate measurement of the aluminum alloy temperature field.Third,the applicability and accuracy of the iterative emissivity model are verified from different angles by means of metallographic experiments,mechanical experiments,EBSD analysis,and numerical simulations.Metallographic experiments were performed by selecting welds with different welding temperatures to investigate whether too low or too high welding temperatures would lead to the formation of internal voids.In the same welding temperature measured using the model,three groups of welds with different process parameters were selected for metallographic experiments,mechanical experiments,and EBSD analysis,and three sets of metallographic images were obtained,with similar mechanical properties and grain size,and the accuracy of the measurements was verified by numerical simulation,which simulated the stir friction welding temperature field for the three groups of parameters,with the same temperature values as measured.In summary,the model can effectively reduce the influence of emissivity in the measurement process and improve the accuracy of infrared thermography in measuring the temperature of aluminum alloys.