Process And Mechanism Research On Semisolid Stirring Brazing Of SiC_P/A356Composites

This paper explores the use fluxless and non-vacuum semisolid stirring brazingprocess to join SiC particulate reinforced A356aluminum matrix composites. The processis a useful method of mechanical stirring semisolid filler metal to disruption and removingof oxide film on the surface of composites. And liquid phase of semisolid filler metal willbe cover surface of composites during the process of the oxide film is disrupted andremoved. Covering of semisolid filler metal on the surface of the composites will promotediffuse between the semisolid filler metal and composites, which also can protect the basemetal from oxidizing again. The bonding temperature is lower than the solidus temperatureof the composites, which can avoid interface reaction of Al4C3between SiC particulate andaluminum matrix.Equipment of semisolid stirring brazing is designed and made under test requirementsand modular principle of design rule. It will make the joining process of SiC particulatereinforced A356aluminum matrix composites simplify, high efficiency and repeatabilityby improving the semisolid stirring brazing equipment in test.The filler metal ZnAl27which is suitable for semisolid stirring brazing SiC_P/A356composites is preliminary designed and made. The effect of the temperature on themicrostructure and solid fraction in Zn27Al filler metal is studied by using semisolidtheory.The effect of process parameter (brazing temperature, stirring rate and welding speed)on the microstructures of joints interface is studied by semisolid stirring brazing equipment.And the bonded ratio of interface, braze metal ratio is used to measure interface brazingability and voids in brazing bead. The joint which the bonded ratio of interface is91.2%,braze metal ratio is94.5%and shear strength is78.5MPa is obtained at brazingtemperature455℃,stirring rate1570rpm and welding speed15mm/min. The bonded ratioof interface and shear strength of the joint of2nd stirring brazing is higher than that joint of1st stirring brazing. Shear strength of second stirring brazing at500(C is113MPa.On the test of disruption and removing of oxide film process, a removing model ofoxide film during semisolid stirring brazing for AlMMCs was established. The disruptionof the oxide film on the substrate is primary accomplished by extruding and frictionbetween solid grains in the filler metal on the surface of the matrix. On the intermediateand final stirring stage, the oxide film is disrupted further with stirring time increasing. At the some time, the diffusion zone formed between filler metal and substrates.The welding defect of semisolid brazing process of SiC_P/A356composites wasinvestigated. Chemical composition of brazing bead is changed by stirrer and voids appearin brazing bead are the main welding defect.