Effect Of Active Elements On Microstructure And Mechanical Properties Of Mo Joint Solded With Sn Based Solder

In the low earth orbit(Leo,200?700 km)environment,there is about 80%of atomic oxygen and 20%of molecular nitrogen have strong oxidation and high relative velocity,which have strong erosion effect on the substrate material Mo,silver plated Mo interconnector or Ag interconnector material commonly used in solar array,making the connection between them unreliable,which will seriously affect the service life of the aircraft.Therefore,it has important application value and theoretical significance to study the low-cost and high reliable connection between Mo back and Mo interconnects of solar cells.In this paper,the first principle calculation method is used to analyze the bonding mode and bonding strength of heterogeneous interface from the atomic level by establishing Mo/Sn,Mo/Al and Mo/Ti models;the best diffusion position of Al or Ti at the interface is analyzed by doping Al or Ti atoms in the Mo/Sn interface.The results show that the Mo-Sn bonding at the Mo/Sn interface is mainly metal bonding,and there are a few covalent bonds at the same time Because of the weak bonding,the separation work of the interface is low,only 1.8 J/m²;most of the Mo-Al bonding at the Mo/Al interface is metal bonding,with a certain amount of ion bonding,and the separation work of the interface reaches 5.84 J/m²;the Mo-Ti bonding at the Mo/Ti interface is mainly metal bonding,with a small amount of ion bonding,and the separation work of the interface reaches 3.91 J/m²is much larger than the separation work of Mo/Sn interface,and Sn surface is the most favorable diffusion site for Al and Ti atoms.The Mo/Mo joint was prepared by ultrasonic assisted brazing with different content of Al(wt.%=0,2,10)in Sn based solder.The effect of Al content on the microstructure and mechanical properties of Mo/Mo interface was studied.The results show that the interface bonding strength is low and the joint fracture is at the interface.With the increase of Al content in the solder,the aggregation of Al element increases and the interface compound changes from Al₅Mo to Al₁₂Mo,The shear strength of the joint increases gradually.When the content of Al is 10%,the shear strength of the joint reaches 33.36 MPa,and the joint breaks in the brazed joint.Adding active element Ti into Sn based solder,the Mo/Mo joint was prepared by ultrasonic assisted brazing.The effect of active element ti on the microstructure and mechanical properties of Mo/Mo interface was studied after different holding time and holding temperature.The test results show that when the holding time is 30 min,the Sn₃Ti₂phase at the interface increases with the increase of holding temperature,the transition layer thickens and the joint shear strength increases;when the holding temperature is 600?,the Sn₃Ti₂phase at the interface increases with the increase of holding time,the transition layer thickens and the joint shear strength increases significantly.When the brazing temperature is 600?and the holding time is 60 min,the shear strength of the joint reaches the maximum value of 24.83 MPa,and the joint is completely broken in the brazing joint.