| The lightweighting of automobiles has made the wall thickness of aluminum radiator fins and flat tubes thinner and thinner,which causes higher requirements on their corrosion resistance.Based on the brazing of aluminum radiators for automobiles,the traditional brazing with soldering can easily cause problems such as joint inclusions and poor corrosion resistance,which need to be improved and developed without flux.The brazing methods in this paper are all contact reactive brazing.The proper process parameters of 3003 aluminum air furnace brazing with flux were studied firstly.Based on this,a new type of Al-Si self-soldering flux was designed,and the optimal composition was optimized through comprehensive analysis by experimental optimization design and thermodynamic software simulation.The prepared solder was then selected to obtain the best solder by analyzing the microstructure and performance.The 3003 base metal was brazed without flux in the vacuum in the presence of the best solder.The influence of different brazing temperatures and holding time on the micro structure and mechanical properties of the joint was studied by analyzing the micro structure,hardness distribution,shear strength and fracture morphology of the joint.The results of brazing with flux in air furnace show that under the conditions of brazing in air furnace at a temperature of 610? for 8min or 620? for 6min and the pressure load is 150g(0.05MPa),excellent brazing joints can be obtained.The solder joint zone is mainly composed of ?(Al)solid solution and eutectic Si.As the brazing temperature increases or the holding time increases,the thickness of the diffusion layer increases.The eutectic Si morphology gradually disperses from an aggregated state and presents a dendritic distribution.The joint side grows into columnar crystals.At the same time,the ?(Al)solid solution gradually spreads towards the central area of the joint,forming a canine tooth staggered bonding interface.The results of design and preparation of self fluxing solder show that Si and Cu are the main impact factors on the liquidus temperature,melting range,hardness,and tensile strength of the solder.The Si content has a chief effect and a negative correlation on the liquidus temperature and melting range of the solder.Cu content plays a primary role and has a positive correlation in the hardness and tensile strength of the solder.The new type of solder is mainly composed of ?(Al)solid solution matrix and eutectic Si,and a small amount of flake/block primary crystal Si phase exists in some solders.In the modified solder,the eutectic Si grains are small,and they cross each other in a network shape.At the same time,there being the obvious phenomenon that eutectic unit cells agglomerate at the multi-point connection.Finally,No.5 solder alloy Al-10Si-Cu-1.5Mg-Mn has suitable organization morphology,good melting characteristics and strong processability with the best comprehensive properties.So it is used as the final solder.The results of brazing on the condition of middle vacuum and without flux show that Using Al-10Si-Cu-1.5Mg-Mn solder,good joints can be obtained at a brazing temperature of 580?600? for 10min or at 600? for 2.5?10min.The solder joint zone is mainly composed of ?(Al)solid solution matrix,primary crystal Si and eutectic Si.Properly increasing the temperature or prolonging the holding time,the eutectic Si content is reduced,the distribution of eutectic Si and primary Si phases is relatively chaotic;the width of the solder joint is increased;The shear strength of the joint and the hardness of each area are continuously improved.The maximum shear strength reached 94.02MPa under the system of 600?×10min,which is about 69.31%of the tensile strength of the base metal.The fracture showes a brittle-tough mixed fracture. |
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