Soldering 6061 Al by Sn9Zn Coating With/Without Two Step Ultrasonic Effect

The work described the effect of soldering 6061 Al by soldering coating with/without two step ultrasonic process, based on Sn9Zn alloy prepared by high frequency melting and rapid solidification. The microstructure, interfacial morphology, shear strength and mechanical morphology of 6061 aluminum alloy soldered joints were compared and analyzed. The results showed that the ultrasonic soldering with coating by two step ultrasonic process technology could greatly improve the morphology of the joints and refine the grain size. The solder layer with larger scallop shape was transformed into a dense fine structure. After two step ultrasonic effect, the width of the joint was about 28% higher than that under the first ultrasonic process. The Zn-rich phase length decreased from an average of 90 µm to an average of 25 µm, about 27% of the original length. The refinement of solder seam was related to the additional dissolved Al and IMC particles. The refinement mechanism was mainly sono-crystallization + sono-fragmentation with two step ultrasonic effect, which was different from the refinement mechanisms of the first ultrasonic effect with sono-crystallization. At the same time, the shear strength of 6061 aluminum alloy joints bonded at low temperature could reach 230 MPa by two step ultrasonic effect. Compared with the ultrasonic soldering with coating, the hardness and maximum strength were improved by 14.5% and 28%, respectively.