| Summary: | A novel lead-free foil (AlMgGaLi) with a melting point of 398.3 ~ 414.8 °C was developed for active soldering of copper to aluminum matrix composite. The effect of joining pressure on the microstructure, interface wetting and shear strength of the dissimilar joints was analyzed. When the joining pressure increased to 1 MPa, an Al-based solid solution with an atomic composition of 89.62% Al, 6.5% Mg, 3.1% O, 0.46% Cu, 0.23% Ga and 0.09% Si was formed within the bond seam and the thickness of the transition layer with copper dissolution was approximately 4.9 μm. The joining pressure improved the interfacial wettability of the dissimilar joint by enhancing mutual diffusion with a shortened interface layer, tailored the runout and the formation of bond seam, and controlled an appropriate thickness of the copper dissolution transition layer. Sound joint with a maximum shear strength of 94 MPa (~ 80% of parent composites) is achievable at 450 °C using the joining pressure of 1 MPa. The failure mechanism of the joints with the AlMgGaLi foil under shear stress has been revealed from the analysis on the interface layers of the joints with SEM/EDX/XRD. Our studies provide an important guideline for using an AlMgGaLi and other similar fillers for a successfully joining of copper to Al-MMCs for high-temperature and high-power electronic devices.
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