Study On Formation Mechanism Of Joints By Ultrasonic-assisted Soldering Aluminum Based And Magnesium Based Materials

Aluminum matrix composites?Al-MMCs?have light weight,low density,high strength,good wear resistance and adjustable thermal expansion coefficient.They have good application prospects,they are essential for application in electronic packaging.However,due to poor weldability,the Si particles are likely to be segregated and the grain grows in a high input state during the welding process,so that the joint strength was not high.Magnesium alloys were commonly used metal materials in aerospace.High-strength welded joints were particularly important,but current welding methods are costly,inefficient,and long-lived,limiting their application in engineering.In this paper,hypereutectic aluminum alloys such as Al-27Si,Al-50Si,magnesium alloys MB8 and AZ31 were studied,and ultrasonic-assisted welding was carried out in the atmosphere and without flux.Compared with the traditional welding method,avoiding the vacuum environment,no flux,short time,high joint strength,no welding defects,achieving low-cost,green,efficient and reliable welding requirements,the specific research contents are as follows:?1?Ultrasonic-assisted soldering was performed on hypereutectic aluminum alloy Al-27Si using Zn-5Al as a soldering filler metal.Different ultrasonic times were applied to obtain a composite weld reinforced with silicon particles.As the ultrasonic time was extended to 64 s,the?-Al and?-Zn in the weld were broken into small fragments,the Si particles were homogenized,and no weld defects were found in the weld.When the ultrasonic time was 64,the shear strength of the joint reaches⁶8.5MPa,which was about two-thirds of the shear strength of the base metal.?2?Ultrasonic-assisted soldering of hypereutectic aluminum alloys Al-27Si and Al-50Si using Zn-5Al as a soldering filler metal.Different ultrasonic times were applied to obtain a composite weld reinforced with silicon particles.When the ultrasonic time is 8s,the oxide film between the base metal and the brazing material was broken,and the ultrasonic wave promotes the migration of the Si particles.When the ultrasonic time was 64s,the composition was uniformized.Different Si particles have different diffusion rates on both sides.By studying the formation of eutectic morphology in the composite weld,the growth mode of the eutectic structure was non-symbiotic-plane growth.The uniform distribution of Si particles in the weld increases the shear strength of the joint.When the ultrasonic time was 64s,the joint strength reaches 70.41 MPa.?3?The Ag-based solder was used as the interlayer,and the bonding of the magnesium alloy was realized by the method of ultrasound-induced transient liquid phase bonding.Ag-28Cu foil was used as the interlayer.Ag-Mg-Cu ternary eutectic reaction was induced between the base metal and the interlayer to form solid solution?-Mg and compound AgMg₃.A small amount of weld microstructure consisting of CuMg₂ and isothermal solidification occurred,and a Mg?Ag,Cu?solid solution was formed.The weld was closed.When the ultrasonic time is 20 s,a metallurgical bond was formed at a ternary eutectic point of 460°C.At room temperature,when the ultrasonic time was 20s,the highest strength of the joint can reach 92MPa,the strength was close to the shear strength of the base metal.When the test temperature reaches 300°C,the strength was 20 MPa,which was about one-fifth of the strength of the base metal.Ag foil was used as the interlayer.The welding temperature of490°C,pressure 0.1MPa and amplitude 6?m were determined.The process parameters lay the foundation for further study of the ultrasonic time on the microstructure and mechanical properties of the weld.