Study On Microstructure Evolution Of Au-Sn Eutectic Alloy During Hot Rolling

Au-Sn Eutectic Alloy is a kind of low-temperature lead-free solder widely used in the field of microelectronics and optoelectronic device encapsulation,which has excellent conductivity,brazing strength and thermal fatigue resistance.The melting point of Au-Sn eutectic alloy is 280?,and the eutectic alloy consists of two intermetallic compounds??-AuSn and??-Au₅Sn?.It has intrinsic brittleness and is difficult to process at room temperature.In this paper,the thermal deformation behavior of Au-Sn eutectic alloy is studied by using the isothermal hot rolling technology.With the characterization technology of SEM,EBSD and XRD,the microstructure evolution in the process of constant temperature deformation is investigated,and the deformation mechanism of the microstructure in the deformation process is also explored.The results were obtained as follows:1.With the use of hot rolling process in constant temperature?235??,the deformation for each one is 5%-15%,it can obtained the preparation for the foil of Au-Sn eutectic alloy?AuSn20.6?.This foil has fine microstructure,smooth surface and neat edges,and its thickness reaches 45?m.2.The study on the microstructure of the eutectic layer in the process of hot rolling shows that the irregular layers of the lamellar group and the interface of the layer group are first coarse.With the increase of deformation,the microstructure of eutectic layer is further coarse,equiaxed,and dynamic recrystallization occurs.Finally,the microstructure of the two-phase eutectic became equiaxed structure?with the Size of 2-5?m?.When the deformation was 50%,75%,90%,95%,99%,the volume fraction of the lamellar group was 1.4%,84.8%,90.2%,99%,100%respectively.The size of the lamellar group is decreased,finally the lamellar group is completely isometric.3.During the hot rolling process,the eutectic layer have rheological deformation,rotation,gradually become small pieces of lamellar group,and equiaxed because of dynamic recrystallization.4.During the hot rolling process,the alloy?which has a small number of primary phase??'-Au₅Sn??deformed,stretching along the rolling direction and gradually breaking.with the increase of deformation,?-AuSn phase has more dynamic recrystallization and precipitation.Eventually it became isometric and melted into the substrate.When the deformation reached 75%,the volume fraction of primary phase became 1.2%?1/3 of the initial cast structure?,and when the deformation was more than 95%,the primary phase was completely integrated into the matrix.5.During the hot rolling process,the EBSD analysis of Alloy microstructure shows that the microstructure orientation of eutectic layer tends to rolling direction,and the dynamic recrystallization occurs in the process of isometric.The primary phase??'-Au₅Sn?in the deformation process,split into multiple orientations from a complete orientation,the small grains of different orientations tilted in order to coordinate deformation.Then the dynamic recrystallization and the precipitation for AuSn phase happened,Eventually it evolved into two-phase isometric structure.