Joining of Advanced Aluminum-Graphite Composite

Advanced aluminum graphite composites have unique thermal properties due to opposite coefficients of thermal expansion of aluminum and graphite. The thermal and mechanical properties of such composites are anisotropic due to directional properties of graphite fibers and their designed orientation. A joint of components with different fiber orientations would theoretically produce an isotropic material for thermal management purpose. This paper presents research results for welding and brazing of the composite using different joining techniques. A laser beam melts the matrix and delaminates graphite fibers. The molten aluminum reacts with graphite to form aluminum carbide Al ₄C ₃. The joint strength is compromised when laser welding at optimal conditions to minimize the carbide formation. Brazing is preferred since the low melting temperature of a filler material suppresses the formation of Al ₄C ₃ while minimizing shrinkage cavities in the joint. Microstructural study and shear test confirm the success of joining this composite by laser brazing and resistance brazing with Zn-Al filler.