Effect of interdiffusion layer of functionally graded Al–Cu composites fabricated by spark plasma sintering on mechanical and thermal properties

Abstract

The effect of the microstructure of multi-layer Al–Cu functionally graded materials (FGMs) fabricated through spark plasma sintering (SPS) on the mechanical and thermal properties was systemically investigated. Uniformly mixed Al–25, 50, 75 Cu (vol%) powder samples were prepared by mechanical ball milling and used for fabricating two types of FGMs: FGM 1 with three layers (Cu/Al–50Cu/Al) and FGM 2 with five layers (Cu/Al–75Cu/Al–50Cu/Al–25Cu/Al). These FGMs were then sintered at 400 °C under a compressive pressure of 250 MPa for 5 min. The microstructures of the sintered FGMs exhibited gradual variations in the Al and Cu contents. An interdiffusion layer composed of Cu9Al4 and CuAl2 at the layer/layer interfaces was observed, the thickness of which was analyzed by energy-dispersive spectroscopy line mapping. The Vickers hardness of FGM 1 and FGM 2 were higher than that calculated by rule of mixture due to the formation of Al–Cu IC such as Cu9Al4 and CuAl2. The drastic enhancement in a Al–75Cu layer was obtained by dominant formation of Cu9Al4. On the other hand, the thermal conductivity of the prepared FGMs was lower than that of Al due to the formation of Al–Cu ICs, enhanced heat dissipation compared with the Al–Cu composite materials. The mechanical and thermal properties of Al–Cu FGMs can be controlled by designing the layer composition or the number of layers.