Ultrasonic-accelerated TLP bonding of 6063 Al with a Mg interlayer: Achieving intermetallic-free joints

The 6063 aluminum alloy is in high demand for automotive and electronic packaging industries; yet, its thermal sensitivity poses challenges for reliable bonding. Transient liquid phase (TLP) bonding has emerged as a promising joining technique for 6063Al, owing to its low heat input and ability to produce solid-solution bonds with superior mechanical properties. Magnesium (Mg), demonstrating high solubility in aluminum, serves as a potential interlayer for achieving intermetallic compound (IMC)-free TLP joints. Nonetheless, its pronounced tendency to form structurally detrimental IMCs, which are inherently brittle and act as crack initiation sites, necessitates impractically long homogenization durations for complete elimination. This study presents ultrasound-assisted transient liquid phase (U-TLP) bonding to address these constraints. Ultrasonic cavitation destroys surface oxides, facilitating rapid liquid phase development, while superimposed ultrasonic and static stresses drive extensive extrusion of the liquid phase. Prolonged ultrasound duration diminishes the interlayer thickness from ∼150 μm to ∼2 μm within 20 s. This rapid squeeze-out establishes a steep Mg concentration gradient, accelerating interdiffusion. Moreover, the narrow composition range of IMC, in conjunction with ultrasound-induced heating and cavitation, synergistically suppresses IMC nucleation and growth. Ultimately, a solid-solution joint is achieved after merely 60 s of ultrasonic treatment without inducing grain coarsening of Al substrate, exhibiting a shear strength of approximately 122.8 MPa. In contrast, conventional vacuum TLP bonding adopting a Mg interlayer of identical thickness requires about 234 h to obtain an IMC-free joint. These findings demonstrate that ultrasonic assistance drastically accelerates interfacial homogenization and improves joint strength by effectively regulating liquid phase behavior and IMC formation.