Interfacial Microstructure Formation Mechanism And Joint Properties On Ultrasonic Soldering Of Fe36Ni Alloy And SiC/Al Composites

Compared with Fe36Ni alloy, which is the traditional material for electronicpackaging, high volume fraction particle reinforced aluminum matrix composites（Al MMCs） have the advantages of low density, low thermal conductivity andadjustable thermal expansion coefficient in certain range, which will be a materialused widely in electronic packaging. But the compact oxide film and numerousceramic particles on the surface are harmful to their weldability, which strictly limittheir application. To realize the joining of Fe36Ni alloy and Al MMCs can not onlyreduce weight, but also increase their thermal conductivity, to improve theirreliability and extend their life. Thus, joining Fe36Ni alloy/Al MMCs hasimportant theoretical significance and potential application. The aim of this paper isto join Fe36Ni alloy and55%SiC_p/A356composites at medium or low temperature.We want to use ultrasonic soldering process with ZnAl and SnZn solder.The excellent wave conductivity of Fe36Ni greatly effects on making a suitableultrasonic soldering process. Firstly, propagation characteristics of ultrasonic waveon the Fe36Ni surface was studied to get the vibration field distribution of Fe36Nialloy plate, and to optimize the suitable location for solder as well as ultrasonicloading mode. Secondly, interface reaction and microstructure of ZnAl/Fe36Niwas investigated. With the addition of Si element into solder, joints were obtainedwith good interfacial bonding, and free of crack. Thirdly, interface reaction andmechanical properties of Sn20Zn/Fe36Ni, as well as interface microstructure aftersolid aging, were systematically investigated, and ideal interface microstructure wasobtained. Forthly, ultrasonic soldering of55%SiC_p/A356composites with SnZnsolder was researched. By studying the effect of Zn content on joints’ microstructureand properties, joints with good interfacial bonding and high strength were realized.Finally, ultrasonic soldering of Fe36Ni alloy and55%SiC_p/A356composites withZnAl and SnZn solder is studied.Software Ansys was approached the modal analysis, harmonic response analysis,and transient analysis of Fe36Ni alloy plate, to get the vibration field distribution.Location with maximum amplitude is located in10-20mm far away from the rightside （area without ultrasonic loading）, which was the suitable position for solder.The spatter loss of solder with ultrasonic time of0.1s was much smaller than that of1s. Thus, ultrasonic time of0.1s was the suitable applying ultrasonic process forFe36Ni, which was to say that multiple short ultrasonic time loading method.The interface reaction of ultrasonic soldering Fe36Ni alloy with ZnAl was so dramatic that lots of compact intermetallic compounds （IMCs） with cracksperpendicular to the interface were observed in joints. The interface structure ofZnAl/Fe36Ni is Fe36Ni/Γ-Fe₄Zn₉/Γ2-Fe₆Ni₅Zn₈₉/Fe-Al+Zn by EDS andlayer-by-layer XRD analysis. A0.1μm thick IMC layer of Fe₄Zn₉（SiO₄）₃compoundwas formed on the interface during ultrasonic soldeing Fe36Ni alloy with ZnAlSi.They appaered stable and their morphology and thickness did not change with theparameters. The compression shear strength of the joints can get up to102-115MPa,and fracture occured at the thin IMC layer. Lastly, model of crack inhibitionmechanism with Si element is raised.SnZn solder was used to ultrasonic soldering Fe36Ni. Interface IMCs weremainly Zn-based compounds with Sn20Zn, and the interface structure of Sn20Zn/Fe36Ni were Fe36Ni/Γ-Fe₄Zn₉/Γ2-Fe₆Ni₅Zn₈₉/Sn20Zn. With increasing thesoldering tempreture and prolonging the holding time, Γ2rich in Ni could transformto Γ2rich in Fe. Shear strength of Sn20Zn/Fe36Ni joints could be up to45-55MPa,fracture occured between the IMC layer and Sn20Zn solder. The interface ractionlayer of Sn20Zn/Fe36Ni after solid aging was stable, the grown rate of which wascontrolled by diffusion, and the grown activation energy of which was6.371kJ/mol.Spreading and wetting behaviors of Sn20Zn solder on55%SiC_p/A356composites were studied with various ultrasonic time, soldering temperature andholding time. When ultrasonic time was more than1s, the oxide film was broken upcompletely, and good wetting between SnZn and SiC was obtained. Maximum shearstrength can be up to108MPa with applying ultrasonic10s+10min+10s. Fractureoccured in the solder near the interface. An amorphous layer of Al₂O₃with200-400nm thick was formed at the interface of Sn and Al by TEM, which strengthenedthe interface bond. An Mg-based amorphous layer was also found at the Sn/SiCinterface. Joints strength of55%SiC_p/A356composites were increased with theinceeasing of Zn content in the solder, and the maximum strength can be up to115MPa with Sn40Zn.Based on ultrasonic soldering of Fe36Ni alloy and55%SiC_p/A356composites,effects of base metal’s position and ultrasonic loading modes on microstructure andproperties of the joints were studied. When the Fe36Ni alloy was the lower plate,and55%SiC_p/A356composites was the upper layer, the joint of two base metals canbe realized, the strength of which can be up to90-114MPa, and fracture occurs atFe36Ni alloy interface. As to SnZn solder, strength of the joints did not change withthe parameters, and was stable at75MPa. A Fe₄Zn₉（SiO₄）₃compound layer wasformed on the SnZn/Fe36Ni interface. With the increasment of Zn content, SiC wasmigrated to the joint by ultrasonic wave. The strength of the joints with Sn40Zn did not change with compared to that with Sn20Zn, and fracture also occurred in thesolder near Fe36Ni alloy interface.