Aluminum Dendrites Reinforced Joints of Ultrasonic Soldering of 2024 Aluminum Alloy with Pure Sn

Ultrasonic soldering of 2024 aluminum alloy with pure Sn filler metal has been investigated. The ultrasonic vibration with 200 w power and at the frequency of 21 kHz was applied on one of the samples to be bonded at 300°C. In this paper, α-Al dendrites reinforced joints were obtained by varying the ultrasonic conditions and the holding time, and the relationship between the volume percent of aluminum dendrites in the joints and the mechanical properties of the joints has been discussed. The solution behavior of Al in Sn under the ultrasonic vibration has been also studied. There are many aluminum dendrites found in the bond, and the maxim mass content of Al in the bond is higher than the solid solution of Al in Sn at the soldering temperature (300°C). It is because that the whole grain boundaries of the aluminum grain will solute to the bond under the ultrasonic vibration, and the aluminum grain separated from the base metal to the bond forming the aluminum dendrites. The model of solution behavior of Al in Sn under the ultrasonic vibration is also presented in this paper.