Transient Liquid Phase Diffusion Bonding of 6061Al-15 wt.% SiC p Composite Using Mixed Cu-Ag Powder Interlayer

Microstructure and shear strength of transient liquid phase diffusion bonded (560 A degrees C, 0.2 MPa) 6061Al-15 wt.% SiCp extruded composite using a 50-A mu m-thick mixed Cu-Ag powder interlayer have been investigated. During isothermal solidification that took 2 h for completion, a ternary liquid phase formed due to diffusion of Cu and Ag in Al. Subsequent cooling formed a ternary phase mixture (alpha-Al + CuAl2 + Ag2Al) upon eutectic solidification. With mixed Cu-Ag powder interlayer, isothermal solidification was faster than for pure Al joints made using a 50-A mu m-thick Cu foil interlayer and for the composite joints made using a 50-A mu m-thick Cu foil/powder interlayer under similar conditions. The presence of brittle eutectic phase mixture (CuAl2 + Ag2Al) led to poor joint strength at short TLP bonding times. The mixture disappeared upon isothermal solidification with a 2-h hold yielding improved joint strength even with solidification shrinkage in the joint. Increased holding time (6 h) erased shrinkage via solid state diffusion and yielded the highest joint strength (87 MPa) and fair joint efficiency (83%).