Study On The Formation Mechanism And Mechanical Properties Of Joints By Rapid Ultrasound-induced Transient Liquid Phase Joining Hypereutectic Al-Si Alloys

Hypereutectic Al-Si alloys are very promising electronic packaging materials due to attractive properties,for example low density,high strength,high thermal conductivity and adjustable thermal-expansion coefficient.It also can match the thermal expansion coefficient of electronic devices,avoid thermal stress damage,heat dissipation and fast heating effect,and has good mechanical properties.However,as a kind of aluminum matrix composite?Al-MMCs?,welding defects are inevitably happened such as precision control,segregation,deleterious interface reaction,due to the different physical and chemical properties of the aluminum matrix.Its high strength and reliable connection are still difficult,and now it has become a bottleneck to restrict the popularization and application of this material.In view of this,based on the effect induced by ultrasonic vibration in liquid phase,the solid/liquid interface and solid phase,ultrasonic-assisted flux-less soldering and rapid ultrasound-induced liquid phase joining of hypereutectic Al-Si alloys are investigated to solve the problems in the joining of Al-MMCs,using a self-assembled ultrasonic-assisted joining system.As a result,Si particles migrate into the joint with the help of ultrasonic vibration,and Si particles reinforced composites joints are obtained.In this paper,microstructure,element behavior,mechanical properties with different ultrasonic-assisted joining process parameters and and the formation mechanism of Si particles reinforced composites joints are analyzed by means of optical microscope,scanning microscope?SEM?accompanied by EDS,nanohardness and strength analyzer,the research results are as follows:1)Based on the role of ultrasound in liquid phase,ultrasonic vibration is introduced into the soldering process of Al-50Si using Zn-5Al filler metal,as a result,Al-50Si alloys are joined by ultrasonic-assisted flux-less soldering in air,and Si particle reinforced Zn-Al based composite joint is obtained.Ultrasonic vibration has effects on removing the oxide film,accelerating Si particles distribution in a Zn-based filler metal,influcing the solidification microstructures of Zn-Al alloys,and also increasing the shear strength of joints.The shear strength of the joint obtained by an ultrasonic vibration time of 96 s can reach to 108.69 MPa,which is about the strength of the base material.2)Rapid ultrasound-induced transient liquid phase joining of Al-50Si alloys has been studied with Zn interlayer at 390 ^oC in air.The research results show that ultrasounic vibration induced Zn-Al binary eutectic liquid phase to join Al-50Si,and obtain Si particles reinforced Zn-Al based composite joints.With the help of ultrasonic vibration,the time required for the isothermal solidification process in the joining process has been shortened.The shear strength and nanoscale hardness increase with prolonging the ultrasonic vibration time,and the mechanical properties of the joint obtained with ultrasonic vibrayion for 128 s are the best.3)Rapid ultrasound-induced ternary eutectic liquid phase joining of Al-50Si has been studied using Ag-28Cu interlayer in air.It is founded that the Al-Ag-Cu ternary eutectic liquid phase is induced by ultrasonic vibrayion,and the formation of Al-Ag-Cu ternary eutectic compounds,including?-Al,??Al₂Cu?and??Ag₂Al?,change with increasing ultrasonic vibration time.With ultrasonic treatment for 15 s,a Si particles reinforced complete isothermal solidification composites joint is obtained.The joint is composed of Al?Ag,Cu?solid solution and Si particles,and the highest shear strength can reach to 123.5 MPa.4)Low temperature and ultrapid ultrasound-induced liquid phase joinings of Al-50Si have been studied using In and Sn-52In interlayer in air,respectively.It is found that an ultrasound-induced Al-In liquid phase is obtained in a ultrapid tme of 0.1 s,Si particles distribute throughout the joint,and Si particles reinforced based composite joints are obtained.Due to the introduction of Sn element into the joint,the complex joints are composed of In_0.2Sn_0.8,Si particles and an Al-In solid solution,and the multi-phase reinforced composite joints are obtained.As a result,the shear strength of the joints increases.The introduction of ultrasonic vibration drives the Si particles in the base metal into the joint,and Si particles reinforced based composite joints are obtained.As a result,the performance of joints can be improved significantly,and the problems existing in the joining of hypereutectic Al-Si alloys have been solved.It lays a foundation for the promotion and application of the material in the electronic packaging products,and opens a new way for the high strength and reliable connection of Al-MMCs.