Interface Behavior And Soldering Mechanism Of Al₂O₃ Particle Reinforced Sn-9Zn Composite Solder Under Low Temperature Wetting Aluminum Alloy

Solder as an ancient way of welding is widely used.With the toxicity of Pb and national ban Pb legislative actions were implemented,traditional Sn-Pb alloys solder is limited.Sn-Zn lead-free solder has the potential to be replace traditional solder because of its low melting point and cost,advanced mechanical properties and Sn-Zn based lead-free solder because of the low melting point and cost,good mechanical properties is expected to replace the traditional solder.However,poor performances in oxidation resistance and wettability resistance limited its applications.In this study,Sn-9Zn solder was used as an example to study the effects of Al₂O₃ particles on the properties of the filler metal and on the mechanism of the low temperature wettability,and its effects on the soldering properties of the filler metal on 6061 aluminum alloy were also systematically investigated by adding different content of Al₂O₃ nano particles and micron nanometer dual size Al₂O₃ particles as reinforced phase by rapid solidification method.The results indicate that the melting point and melting range of the solder adding Al₂O₃ particles to Sn-9Zn decrease slightly compared to Sn-9Zn solder.Melting point of Sn-9Zn-1Al₂O₃?nm?-0.75Al₂O₃??m?reduce 1.5? compared to plain Sn-9Zn solder.The length of the Sn-9Zn eutectic structure distributed on the ?-Sn matrix of composite solder becomes shorter and distributed more evenly.By adding micro-nano-sized Al₂O₃ particles,the needle-liked Sn-Zn eutectic in the microstructure of the composite solder was changed into uniform and fine patchy ones,in which Sn-9Zn-1Al₂O₃?nm?-0.75Al₂O₃??m?tends to have the smallest size of Sn-Zn eutectic in the microstructure and the distribution space is lager and its number is smaller.At the same time,the microhardness and tensile strength of the composite solder are increased by the addition of Al₂O₃ nanoparticles,and the elongation got decreased.The hardness and tensile strength of the composite solder firstly increased and then decreased with the addition of micro nano double size Al₂O₃ particles.As a result of the hindrance of the Al₂O₃ particles to the dislocation movement and its inhibitory effect on the growth of Sn-Zn eutectic structure,the microhardness of Sn-9Zn-1Al₂O₃?nm?-0.75Al₂O₃??m?composite solder increased by 21.6%,and the tensile strength increased by 18.6%,respectively compared with the original Sn-9Zn solder.Composite solder prepared by adding different components of Al₂O₃ particles to Sn-9Zn matrix all tends to have a good wetting effect on 6061 aluminum alloy.For Sn-9Zn-1Al₂O₃?nm?-0.75Al₂O₃??m?double size particle reinforced composite solder,the maximum spread area on 6061 aluminum alloy is 113.2mm2,increased by 182% compared to Sn-9Zn solder.The reason is that the addition of Al₂O₃ nanoparticles or double-sized Al₂O₃ particles on the soldering filler metal have an inhibitory effect to Al8 Zn Sn4 solid solution of Aluminum alloy wetting interface as well as its effect on the improvement of morphology.The analysis of the kinetics of the diffusion of 6061 aluminum alloy by the soldering filler metal of Sn-9Zn reinforced by Al₂O₃ nanoparticles shows that the time of the wetting process can be shortened by the addition of the reinforced phase of Al₂O₃ nanoparticles,the main manifestations are rapid control stage and reaction control stage.The time required for the rapid control phase of Sn-9Zn-1Al₂O₃?nm?composite solder is shortened by about 0.4s,and the time of the reaction control phase is shortened by about 2.8s.In addition,the Al₂O₃ nanoparticles decrease the ??N?at the diffusion control stage of the composite solder,and the macroscopic performance is the spreading area of composite soldering filler metal on 6061 aluminum alloys is increased.The microstructure of the composite solder prepared by adding Al₂O₃ particles to the Sn-9Zn matrix showed a tendency to be fine first then rough.Correspond that the shape ofAl₈ ZnSn₄ solid solution layer changed from scallop to straight,and its thickness also showed the tendency to become thinner.The hardness of the soldering filler metal prepared by adding Al₂O₃ particles to the Sn-9Zn matrix and the microhardness of the Al₈ZnSn₄ solid solution layer in the soldering filler metal showed a tendency to increase first and then decrease.The hardness of soldering joint structure of Sn-9Zn-1Al₂O₃?nm?-0.75Al₂O₃??m?composite soldering filler metal and of the interface is 29Hv0.3 and 40.3Hv0.3,which is increased by 25.5% and 17.3% compared with the original Sn-9Zn composite solder,respectively.The hardness of soldering joint of Sn-9Zn-1 Al₂O₃?nm?-0.75Al₂O₃??m?composite soldering filler metal is 29Hv0.3 and 40.3Hv0.3,the reason is that the Al₂O₃ particles melted inside the solder have a hindrance to the dislocation movement and the refinement of the solder.The shear strength of soldering joint shows a tendency to decrease after the process of increasement.Joint shear strength of Sn-9Zn-1Al₂O₃?nm?-0.75Al₂O₃??m?composite solder is 43 MPa,increased by 54.1% compared to the original Sn-9Zn solder.All aluminum soldering joints have dimples and the size varies.The number of dimples in the fracture surface of Sn-9Zn-1Al₂O₃?nm?-0.75 Al₂O₃??m?soldering joint is the largest and the size is more small and the distribution is more uniform,showing a typical toughness fracture.