Study On The Sagging Resistance Of The Aluminum Clad Sheet Of Heat Exchanger By Processing Technology And Brazing Process

Since the aluminum alloy has the characteristics of light weight,high strength and good thermal conductivity,the aluminum foil is used to replace the original copper fin which can reduce the weight.By thinning the thickness of the fin to further reduce vehicle weight,but aluminum foil is prone to collapse at elevated temperature,which causes the heat exchanger to be scrapped.Therefore,it is necessary to have a high temperature resistance to deformation of the aluminum foil fin to ensure that no obvious deformation occurs in the brazing.In order to ensure that the heat exchanger will not collapse,the heat exchanger manufacturers usually put forward some requirements for the sagging value of aluminum foil.The effects of different intermediate annealing,final rolling reduction,finished annealing and brazing process on the microstructure and sagging performance of composite aluminum foil were studied by means of metallographic observation,scanning electron microscopy,transmission electron microscopy,tensile test and sagging test,the theoretical basis and guidance for the practical production and process planning are provided.The main conclusions of this paper are as follows:(1)The effects of different intermediate annealing(330?/2h,420?/2h)and final rolling reduction(20%-50%)on the microstructure and properties of the aluminum foil were studied.Composite aluminum foil has the best anti-sag properties when the intermediate annealing is 330?/2h,and the final rolling reduction is between 30% and 40%.(2)The sagging behavior of the composite aluminum foil with the intermediate annealing of 330?/2h and final rolling reduction between 20% and 50% was analyzed.30% and 40% final rolling reduction of the aluminum foil was obtained the coarse grain structure and high sagging resistance,but the sagging performance of aluminum foil with 20% and 50% final rolling ratio is poor.(3)The sagging behavior of the composite aluminum foil can be divided into fast sagging stage?slow sagging stage and erosion stage.The sagging stage?slow sagging stage and erosion stage occur in the recovery?crystallization stage and heat preservation of 600? respectively.(4)The effect of 330?/3h final annealing on the performance of the composite aluminum foil was studied.The sagging performance of aluminum foil with 40% final rolling reduction can be improved by final annealing,but the sagging resistance of the sample with 90% reduction is not improved by final annealing with 270?/3h.The grain structure of composite aluminum foil was not significantly changed by final annealing of 270?/3h.(5)The effect of preheating 1 hour at different temperature,brazing heating rate and brazing holding time on the erosion of aluminum foil was studied by DSC technique.Shortening the holding time at high temperature and increasing the heating rate is helpful to reduce the influence of erosion.heat preservation of 600? for a long time or too fast or slow heating rate will reduce the resistance of composite aluminum foil.