The Influence of temperature on the microstructure and properties of Cu/Al tube joints in magnetic pulse-assisted semi-solid brazing

Abstract

This study addresses the technical challenge of copper/aluminum (Cu/Al) tube joining through the innovative application of magnetic pulse-assisted semi-solid brazing (MPASSB) technology. Through an integrated approach combining finite element simulation with microstructural characterization, this study systematically investigates how brazing temperature (390–440 °C) influences the microstructure and mechanical properties of Cu/Al tube joints. Notably, a novel finite element method-smoothed particle hydrodynamics (FEM-SPH) coupling model has been developed. This model enables precise simulation of fluid-solid interactions between tubes and filler metal during the brazing process, providing fresh insights into oxide layer removal mechanisms. The research reveals that brazing temperature serves as the critical parameter governing the elemental diffusion and microstructural evolution in the joint. As the temperature increases from 390 °C to 440 °C, the viscosity coefficient of the filler metal decreases significantly from 41.6Pa·s to 1.798Pa·s, resulting in enhanced fluidity that promotes interfacial interactions between the tubes and filler metal and effectively removes surface oxide films, thus improving joint quality. However, excessive temperature intensifies the filler metal ejection, increasing the risk of filler metal deficiency at the top of the joint. Mechanical testing demonstrates that joints brazed at 440 °C achieve optimal shear strength of 81.1 MPa, with fracture occurring at the copper-side (Cu-side) interface between the Al_4.2Cu_3.2Zn_0.7 intermetallic phase and the diffusion layer. This work establishes fundamental theoretical guidance for optimizing MPASSB process parameters and facilitates the efficient joining of Cu/Al tubes.