Research On Double Size Particle Reinforced Sn9Zn Composite Brazing Filler Metal And 6061Al Low Temperature Brazing Technology

With the development of the soldering field,the requirements of new soldering materials and processes are getting higher.Due to the excellent properties,Sn9Zn solder was used widely in the field of aluminum alloy soldering,but the joint strength was limited because of the presence of Zn and the limitations of the soldering process.In order to modify this shortcoming,the performance of the solder was improved by adding micro-nano particles as reinforcing phases,and different soldering processes of aluminum alloy was explored to study the interface bonding problem.In this experiment,Sn9Zn-0.75SiC(?m)-xGraphene nanosheets(GNSs)(x=0,0.25,0.5,0.75 and 1.0wt.%)and Sn9Zn-0.75SiC(?m)-xSiC(nm)(x=0,0.25,0.5,0.75and 1.0wt.%)composite solders were smelted and produced,and different processes on 6061Al soldered with GNSs addition were explored.According to the microscopic characterization and formula calculation,the influence of micro-nano particles on the micro-structure and the interface of the joints were discussed,and the enhancement and refinement mechanism of the micro-nano particles were explained.The addition of nano-particles could effectively improve the wetting ability to6061Al.For flux-assisted wetting 6061Al,when the content of GNSs and SiC nanoparticles reached 0.75wt.%,the wetting angle were 26°and 31°,and compared with the Sn9Zn-0.75SiC(?m)solder,reduced by 27.78%and 14.23%,respectively.For ultrasonic-assisted wetting 6061Al,when the content of GNSs and SiC nanoparticles reached 0.75wt.%,the spreading area reached 98.3mm²and 96.1mm²,respectively.Compared with the Sn9Zn-0.75SiC(?m)composite solder,it increased24.43%and 21.52%,respectively.The addition of nanoparticles could significantly upgrade the mechanical properties of the composite solders.As for the refinement mechanism,the addition of nanoparticles greatly reduced the nucleation-free zone and increased the nucleation core in the solder,thereby effectively promoted grain refinement.Under the influence of micro-nano particles,the Zn-rich phases was significantly reduced.As for Sn-Zn eutectic structure,the shape changed from rod-like to needle-like,and finally to spherical,and had a regionally directional arrangement.When the content of GNSs and SiC nanoparticles reached 0.75wt.%,the refinement of the Sn-Zn eutectic structure was most obviously manifested as needle-like arrangement,and compared with no nanoparticles addition,the width of Sn-Zn eutectic was reduced by 31.11%and 78.95%,respectively.And the ultimate tensile strength reached 85Mpa and82.1Mpa,and the elongation reached 48%and 46%.Compared with the Sn9Zn-0.75SiC(?m)composite solder,the tensile strength increased about 37.11%and 28.13%,respectively.And the elongation increased about 380%and 130%,respectively.The strengthening method of composite solders was mainly caused by grain refinement and dislocation enhancement.For the soldered joints with GNSs addition,the soldering processes of flux-assisted,primary ultrasound-assisted and dual ultrasound-assisted were discussed.Different soldering processes showed different degrees of refinement to the joint structure.When the content of GNSs reached 0.75wt.%,compared the joint with no GNSs addition,the width of the Sn-Zn eutectic structure was reduced by57.89%,76.84%and 87.37%,respectively.Especially in the dual ultrasound-assisted,the arrangement density of Sn-Zn eutectic reached the highest,and the interface layer changed significantly.The XRD analysis showed that there was Al₄C₃-IMC distribution at the interface,and the interface layer was Al-Zn solid solution layer(Al_0.71Zn_0.29and Al_0.403Zn_0.597).The increase of Al-C bond and Al-Zn bond effectively enhanced the interface.When the content of GNSs was 0.75wt.%,the shear strength reached 132.6Mpa,160.1Mpa and 241Mpa,respectively.And the ductility reached11.5%,14.2%and 13.5%,respectively.Compared with no GNSs addition,the shear strength increased about 38.9%,42.8%and 107.7%,respectively.And the ductility increased about 8%,12.1%and 11.2%,respectively.For flux-assisted soldering,the grain refinement and dislocation strengthening were the main factors,accounting for about 46.92%of the total joint strength.For ultrasonic-assisted soldering,the grain refinement,the dislocations strengthening and Orowan strengthening were the main factors,accounting for about 49.23%and 43.98%,respectively.Different soldering processes had different effects on the joint structure.When the content of GNSs was0.75wt.%,the flux process was reduced by about 4.92%,but the primary and the dual ultrasound increased by 17.69%and 50.12%,respectively.The optimal soldering process was the dual ultrasonic-assisted process,the ultrasonic power was 350W and the ultrasonic time was 2s+5s.