Technology And Mechanism Research On In-situ Reaction Brazing Of SiCp/Al Composites With High Particle Volume Fraction

With the properties of light weight,high efficiency and low costs,SiCp/Al composites with high particle volume fraction have been widely used in the electronic packaging and thermal control components within aviation,aerospace vehicle's and electronic countermeasure,bringing great attention to electronic countenneasure,economic construction and social development.Because 70%SiCp/Al composites contain a high proportion of reinforced particles and their physicochemical properties have great differences with that of substrate,the quality of welded joint is hard to meet the producing requirements.In this thesis,the author proposes in-situ pressurized brazing,prepares brazing filler metals containing Ti suitable for the composites,and explores the influence of different Ti contents and different technology on welding performance.And at last,the author obtains reliable welded joint and studies metallurgical bonding mechanism of composite in-situ pressurized brazing and Ti's function mechanism.This thesis proposes in-situ reaction brazing.The brazing filler metal power is added in the compound to be welded,and the compound was welded under the circumstance of pressure and vacuum.Under the pressure,atoms diffuses,in-situ liquid phase comes into being,in-situ reaction reacts,liquid brazing joint consolidates and metallurgical bonding interface are formed between brazing joint and parent metal.The essence is to improve wettability of brazing filler metal,form new reinforcement phase,improve interface performance,enhance interface bonding force,and to increase joint property by in-situ reaction.The author prepares Al-Si-Ti brazing filler metal with four different Ti contents,and the experiments go on under different welding conditions of different temperatures and pressures.When the brazing filler metal contained 10%Ti,the temperature interval of solid-liquid phase was 549.0?604.8? and wetting angle was 40°,the author found that under the welding condition of 640?,6MPa and 1.5h,the in-situ pressurized brazing with the 10%Ti filler metal achieved the joint of best performance,whose shear strength reached 149.68MPa,closing to 50%of parent metal's.By in-situ pressurized brazing,the Al,Si,Ti elements in the filler metal formed new block or ring Ti7Al5Si12 compounds through in-situ reaction,which enhances the metallurgical bonding of weld metal.What's more,the reaction between SiC particles in the surface of the composites and Ti forms flocculent Ti7Al5Si12 compound in the surface,and transforms the"SiC/filler metal" interface into“SiC/Ti7Al5Si12/filler metal" interface,increasing the interface bonding force.Block or ring Ti7Al5Si12 compounds are formed in the weld joint accompanying with dispersive distribution,to improve in-situ reinforcement effect in the weld joint.In addition,the formation of Ti7Al5Si12 compound also transforms the wetting process in the composites surface into reactive wetting,improve the wettability of filler metal,and in the same time,avoiding the generation of Al4C3 and Al2O3 in conventional welding technology.