Preparation Of Sn9Zn Nano-composite Solder And Low-temperature Soldering Behavior On Aluminum Alloy

Due to their lower density,excellent electrical and thermal conductivities,aluminum alloy has been widely applied in LED,heat exchangers of waveguide section,etc.Therefore,low temperature soldering has been emerged to be the preferred method to ensure the location and accuracy of working part,which have attracted intensive researches in recent years.Sn-Zn eutectic alloys have been widely acknowledged as the most convenient and reliable solders for low-temperature soldering of aluminum alloy.However,the aluminum alloys for LED need to soldered below 180℃,and there is no available solder at present.Many studies have found that the nano-solders can provide denser joints and better reliability.Therefore,as low-temperature soldering material,the investigation on Sn-Zn nano-particles is of great significance,which makes it become one of the new subjects in the field of LED recent years.To realize low temperature and low pressure soldering without plating,the purpose of this paper is to determine the optimum content of PVP for the preparation of nano-particles,and based on the Sn-9Zn nano-particles,nano-composite solder reinforced with Al₂O₃ nano-particles were obtained by adding different components of Al₂O₃ nano-particles,and then applied the nano-particles to low-temperature soldering by taking advantage of its nano-size effect,and then study of its interconnection.The influence of soldering parameters（soldering temperature and holding time）on the microstructure and mechanical properties of the joint was systematically studied.The formation mechanism of the soldered joint was analyzed by means of SEM,EDS and XRD.The optimum soldering process parameters and the composition ratio of the solder are obtained.In the present study,Sn9Zn nano-amorphous particles with low melting temperature were synthesized by chemical reduction method.The results revealed that PVP concentrations significantly affect the size distribution and melting point of the nano-particles.When the amount of PVP is 10wt.%,the size of nano-particles is 23nm,which is 21.7%lower than that of Sn9Zn-P5.The melting point is in good agreement with the particle size.The corresponding melting point of the former is 10.34%lower than the latter.And X-ray powder diffraction results revealed that increasing content of PVP can significantly promote the fraction of the amorphous phase.The as-synthesized Sn9Zn nano-solders were used to solder the 6061 Al alloy.Sn9Zn-P10 nano-solder can be welded at a temperature below 180℃,whose joint is corresponding to the minimum porosity.And its shear strength can reach about 17.6MPa,and the corresponding soldered joint microstructure is denser,and the location of the fracture is mainly located in the solder layer,showing the characteristics of plastic fracture.Through the comprehensive study of microstructure and X-ray diffraction of the joints,it can be concluded that good metallurgical bonding is achieved between the 6061 Al alloy and the sintered Sn9Zn nano-particles,resulting in a layer of Al₂Zn₃ at the interface,which is the result of rapid diffusion between the Zn atom and parent metals.And its corresponding shear strength of soldered joints increased by 8.64%compared with that soldered by Sn9Zn-P5.The PVP content has a significant effect on the metallurgical reaction between the nano-solder and the parent metal.When the content of PVP is 10wt.%,the soldering effect is the best.The influence of the content of Al₂O₃ particles and soldering parameters on the microstructure and mechanical properties of the joint was systematically studied.With the increase of soldering temperature,the shear strength increased firstly and then decreased.When the soldering temperature is increased to 180℃,the corresponding shear strength is increased by 38.58%compared with that solder at 160℃.With the increasement of the holding time,the mechanical properties of the joint showed an upward trend.The shear strength corresponding to the dwell time of 5 min increased by 37.5%compared with the dwell time of 3 min.For the microstructure of the joint,it was found that with the increasement of the soldering temperature and the holding time,the microstructure of the joint become denser and the thickness of the diffusion layer increased.The melting point of the Sn-9Zn solder is greatly decreased by adding Al₂O₃ particles,and the melting point of Sn9Zn-5Al₂O₃ is 1.21℃lower than that of Sn9Zn nano-solder.The shear strength of the joints soldered by nano-composite solder increased firstly and then decreases,whose corresponding microstructure of the joint presents the trend of refined firstly and then coarsen.The joints of 6061 aluminum alloy soldered with Sn9Zn-5Al₂O₃have good connection performance,and dimples appear at the fracture,showing the characteristics of ductile fracture.And the shear strength of the joints soldered by Sn9Zn-5Al₂O₃ is increased by nearly 4.6%compared with the Sn9Zn nano-solder.When the addition of nano Al₂O₃ particles is 10wt.%,the segregation of Al₂O₃ particles appears in the cross section.For a crack source,the joint performance becomes worse and the shear strength is 17.7Mpa.