Research On Ultrasonic Soldering Technilogy And Joint Reliability Of SiC_p/Al Composites

SiC particle reinforced aluminum matrix composites(SiC_p/Al MMCs)have the advantages of low density,high thermal conductivity and adjustable thermal expansion coefficient in certain range,making it an ideal material for electronic packages in aerospace,instrumentation,automotive manufacturing and other fields.However,SiC ceramic particles and matrix aluminum alloy in the composites are difficult to be wetted with Sn base solders,which makes it difficult to realize low temperature brazing.Therefore,in this paper,ultrasonic brazing was used to conduct low temperature joining of SiC_p/Al MMCs.The forming law,mechanical properties and the evolution of the microstructure of the brazed joint was studied.In addition,the Abaqus finite element analysis software was used to simulate the residual stress and thermal cycle process of the joint,so as to evaluate the reliability of the joint.The ultrasonic brazing process of SiC_p/Al MMCs was studied.Under the treatment of short time ultrasound,it was found that there were some pores in the joint.Ultrasonic treating can promote the flow of solder and drive the discharge of gas in the weld.By extending the ultrasonic treating time,the degree of the oxide film breaking on the base material surface was gradually increased,and the oxide film at the front of the joint was broken before that at the end of the joint.When ultrasonic treating was applied for 5s,the pores in the welding joint can be completely vented out.And the oxide film on the surface of the SiC_p/Al MMCs can also be broken and removed thoroughly.Thus,a well-formed brazing joint without any defects was obtained.Then,the treating time of ultrasound was further extended,making the Al element in the base metal persistently migrate to the Sn9 Zn solder.Finally,the Al element distributed uniformly in the whole solder,instead of only distributed at the interface between the SiC_p/Al MMCs and the solder.With the extension of the ultrasonic treating time,the shear strength of the joint first increases to about 65 Mpa and then remains at the same value.The increase in shear strength of the joint is caused by the breaking and removing of the oxide film and the increase in the content of Al element in solder.After the oxide film is completely removed and the content of Al element in the weld reaches saturation,the shear strength of the joint would not increase anymore.According to the simulation results of residual stress and thermal cycle process of SiC_p/Al MMCs joints,the residual stress,which is small in the parent metal,is concentrated in the solder layer(about 50MPa).The stress distribution in the solder layer is uniform and the plastic deformation is small,which means the ductile damage can hardly occur.The thermal cycling process could relieve the plastic deformation of the joint and reduce the stress level of the whole joint.The continuous thermal cycling process would not persistently increase the plastic strain energy density and ductile damage coefficient of the joint.Therefore,after thousands of times of thermal cycling,the joint would not suffer fatigue damage based on energy standard,nor reach the ductile damage criteria.Therefore,the joint has high reliability that meets the requirements of electronic packaging and some other fields.