Microstructure evolution and mechanical properties of ultrasonic-assisted soldering joints of 2024 aluminum alloys

Ultrasonic-assisted soldering of 2024 aluminum alloys using a filler metal of Zn-5Al alloy was investigated at the temperature of 400 °C, which is lower than the solution strengthening temperature of Al-Cu alloys. The ultrasonic vibration with power of 200 W and vibration amplitude of 15 μm at the frequency of 21 kHz was applied on the top samples. The ultrasonic vibration promoted the dissolution of Al elements in the base metal. The reduction of volume fraction of the eutectic phases in the bonds was investigated by increasing ultrasonic vibration time. As the ultrasonic vibration time increased from 3 s to 30 s, the volume fraction of the eutectic phase in the bonds decreased from 12.9% to 0.9%, and the shear strength of the joints was up to 149-153 MPa, increased by 20%. The improvement of the mechanical properties of joints was discussed based on the modulus and hardness of the phases in the bonds and the fracture of the joints.