Study On Low And Medium Temperature Ultrasound-assisted Soldering Of RSA-708 Aluminum

Ultra-high strength aluminum alloy is foreseen as a promising alternative to conventional alloys in manufacturing industries, owing to its excellent strength,surfactivity and corrosion resistance. Excessive heat imput, however, may result in recrystallization and grain growth, destroying the refined structure of ultra-high strength aluminum, which forbids most the use of most welding techniques. This article investigated the influence of temperature, heating rate and holding time on the microstructure and strength of the brazed joint of RSA-708 ultra-high strength aluminum. An ultrasound Transient liquid phase bonding method was designed.Results showed that the strength of RSA-708 aluminum decreased with higher brazing temperature and longer holding time. Ductility of the allloy increases as strength declines. During heat treatment, the microstructure of RSA-708 alloy recrystallized to equiaxed grains with no distortion. Grain size didn’t increase significantly as processing temperature or holding time increases.Sn based solders were used in soldering RSA-708 alloys. Joints was soldered with Sn-Bi-Pb-Zn and Sn-Bi-Zn alloy at 170°C and 200°C respectively. The diffusion and dissolution at the interface of aluminum and solder was weak.Brittle lamellar structures composed of Sn-Bi eutectic formed in the soldering seam. Shear strength was only 60 MPa.Joints was soldered with Sn-9Zn alloys under 250°C. Diffusion and dissolution at aluminum interface was promoted by prolonging ultrasound action time. Tensile strength of the joints reached 180 MPa, which showed insignificant relevance with ultrasound time and the width of brazing seam.A method for soldering RSA-708 aluminum with Zn-Al alloys was designed.Joints soldered with pure Zn and Zn-5Al alloys each reached 263~284MPa,120~211MPa respectively. Microstructures of Zn-5Al joints were refined by adding Cu to solder. By increasing ultrasound time to 30 s, the volume fraction ofα-Al increased and joint reached 255 MPa.A method for joining RSA-708 alloy with ultrasound assisted transient liquid phase bonding technique was modified. Isothermal solidification and homogenization of the joint structure was enhenced by increasing the ultrasound and holding time. Shear strength of the joint reached 210 MPa with appropriate parameters.