Growth behavior of intermetallics with discontinuous distribution of Cu/Al/Cu trilayered composites during annealing

To elucidate the growth behavior of discontinuously distributed intermetallics during annealing, Cu/Al/Cu trilayered composites were fabricated via high-temperature oxygen-free rolling. The interfacial microstructure evolution, formation thermodynamics, and growth kinetics were systematically investigated under various annealing treatments. Microstructural characterization revealed that the interface parallel to the rolling direction in the Cu/Al/Cu trilayered composites consisted of discontinuously distributed Al 4 Cu 9 , AlCu, and Al 2 Cu phases, resulting in a dual interfacial bonding mechanism involving both metallurgical bonding and mechanical bonding. The thickness of the intermetallics layer increased progressively with increasing annealing temperature and annealing time. Quantitative analysis showed that the growth of the intermetallics layer followed a parabolic kinetic law, which is in good agreement with the classical diffusion-controlled growth model. The growth rate constant exhibits a strong temperature dependence, increasing significantly with elevated annealing temperatures. The annealing temperature exerts a more pronounced influence on intermetallics layer thickness than annealing time. Notably, intermetallics on both sides of the discontinuous region gradually grew toward each other and ultimately bridged the interfacial gap during prolonged annealing. The spacing between discontinuously distributed regions gradually decreased until the intermetallics formed a continuous layer, thereby progressively transforming the interfacial bonding into metallurgical bonding. Al 4 Cu 9 and Al 2 Cu tend to grow more easily than AlCu during annealing, and the intermetallics grew faster toward the aluminum layer than toward the copper layer. The discontinuously distributed intermetallics create numerous preferential diffusion pathways during annealing. This unique microstructure significantly reduces elemental diffusion resistance, decreases the activation energy of intermetallics formation, and promotes nucleation and growth kinetics compared to continuous interfacial intermetallics.