Transmission electron microscopy of an ultrasonically consolidated copper–aluminum interface

Ultrasonic consolidation is a rapid manufacturing process for metal matrix composite (MMC) preimpregnated composite (prepreg) tapes or foils. One of the main advantages of this manufacturing technique over traditional MMC methods is the ability to produce multimaterial structures through the layer-by-layer build-up procedure. The interface of an ultrasonically consolidated bimaterial interface has not been studied on the nanometer scale through transmission electron microscopy (TEM), which can help better understand the bonding mechanisms. An ultrasonically consolidated copper–aluminum (Cu–Al) interface was explored through TEM, through which a 1-µm recrystallized subgrain region was observed on the aluminum side and dislocation pile-up was viewed between the subgrain and bulk aluminum interface. Phase changes were suspected due to varying contrast bands parallel to the Cu–Al interface and were confirmed through an x-ray energy dispersive spectroscopy (XEDS) linescan. An apparent diffusion coefficient was calculated, which supported bulk diffusion at the measured welding temperature of 493 °C and subgrain size of 20–50 nm.