Research On Braze Welding Procedure Of Automobile Heat Exchanger In Nitrogen Oven

Heat exchanger is a kind of industrial product,which is widely applied in modern society. With the developments of novel design for high-dense, high heat efficiency, small gravity and low cost, the more critical demanding of the quality of brazed joint in Al heat exchanger is proposed. In this dissertation, based on the actual brazed joint quality problems of"Yudian-Ⅲ"Al heat exchanger, several impacting aspects were analyzed. Brazing temperature was mainly studied to the influence of brazed joint quality, and optimally setting temperature was found by using the method of experiment and numerical simulation.In this paper, we firstly analyzed brazing set temperature of 800mm/min net speed. Based on production actuality of"Yudian-Ⅲ"Al condenser, net speed: 800mm/min,density of flux: 5%,drying temperature: 230℃,N2 purity:≥99.9995%, welding procedure was confirmed logically by changing brazing set temperature. From 595℃to 625℃,with 5℃as temperature gradient, every sample piece was brazed one by one, brazed joints in different temperature were analyzed by using water pressure test,helium gas leak test,salt spray test and metallurgical structure. The results showed that optimally setting temperature is 610℃-615℃, net speed: 800mm/min,density of flux: 5%,drying temperature: 230℃,N2 purity:≥99.9995%.Secondly, we studied the influence of element diffusion to joint formation. Phenomenon and principle of braze welding procedure were analyzed through the diffusion behavior of Silicon,change of brazing seam texture and migration of brazed joint. It also testified that the Silicon diffusion exists during the ramp-up period and that the phenomenon of the so-called Silicon depleted zone was caused. It showed that the phenomenon of matrix solution enlarge as brazing temperature or dwell time became higher. The essence of phenomenon is the results of diffusion behavior between solid phase and liquid phase.In the end, based on brazing set temperature gotten from the experiment, FEM was utilized to study the thermal distribution in Al heat exchanger by the software ANSYS. The numerical simulated results were in good agreement with the experimental data. According to the production demand, processing project were optimized, and the productive efficiency increased as well as net speed were increased to 1200mm/min. Brazing temperature was predicted in advance by the software ANSYS, then the project was demonstrated by experiments. The results showed that increasing brazing set temperature to 685℃can get good brazed joints. It indicates that the way of numerical simulation is feasible. It can not only shorten technological testing periodic time and reduce cost, but also improve productive efficiency.