Microstructure Refinement Technology And Mechanism Of Ultrasonic-assisted Brazing Particle Reinforced Aluminum Matrix Composite

Ultrasonic-assisted brazing uses ultrasonic cavitation and ultrasonic flow effect to improve the wettability between ceramic particles and solder,and achieves no flux connection of SiC_p/Al-MMCs in the atmosphere.The ultrasonic cavitation effect can break the dendrite in the welding joint and improve the mechanical properties of the joint.However,its mechanical properties are limited by the properties of solder,so it is often difficult to be applied to structures with high strength requirements.In order to break through the limitations of traditional ultrasonic-assisted welding SiC_p/Al-MMCs.In this paper,for the ultrasonic-assisted brazing of50 vol.%SiC_p/6061Al,a method of applying secondary ultrasonic in the solidification process of liquid solder is proposed.the effect of the ultrasonic cavitation and the ultrasonic flow effect on the solid-liquid solder of different proportion is different.To explore the mechanism of ultrasonic excitation in narrow gap on grain refinement in semi-solid state of solder.In order to refine the grain size of the welding joint and improve the mechanical properties of the joint.When Zn-Al solder was used,it was found that the further refinement of?-Al phase could be realized by applying secondary ultrasound when the solder was cooled to semi-solid state.SiC particles in the welding joint were evenly distributed with?-Al,and the mechanical properties of the joints were greatly improved.The shear strength of the joint was up to 245.17 MPa,and the shear strength of the joint was increased by 65%when the secondary ultrasonic was not applied.When Sn-Zn solder was used,the Zn-rich phase produced in the welded joint was broken and refined by ultrasonic cavitation effect,and the ultrasonic flow effect promoted the dissolution of aluminum in the base metal to the welding joint.With the increase of ultrasonic application time,the number and size of Zn-rich phase decreased gradually,and more?-Al phase precipitated in welded joint.The maximum shear strength was 74.17 MPa,which was60%higher than that without secondary ultrasound.However,excessive secondary ultrasound would cause solder atomization and seriously affect the mechanical properties of the joint.Based on the analysis of microstructure,fracture morphology and mechanical properties of welded joint,the mechanism of secondary ultrasonic action on microstructure of solder in narrow gap was revealed,which realized the control of microstructure in welding joint and improved the mechanical properties of brazed joint.