An Experimental Study of the Densification Mechanism in Semi-solid Powder Forming of Diamond/Al-Alloy Matrix Composite

Diamond/Al-alloy composite, with its features of high thermal conductivity and low density, is one kind of recently developed lightweight heat dissipation material. In this paper, a novel method of semi-solid powder forming (SSPF), a fabrication method that exploits the unique behavior of a liquid-solid mixture, is used to fabricate the diamond/Al-alloy composite. The Al-alloy matrix is designed as a bi-metal system, including an Al-alloy powder with higher melting temperature acting as solid flexible skeleton to support the diamond, and another with lower melting temperature acting as liquid filler to fill pores between powder gaps. The density, electrical conductivity, thermal conductivity, and microstructure of the composites were studied. Results show that the interface wettability and plastic deformation are encouraged while the sintering temperature is increased from 753 K to 833 K, which helps to increase the relative density of the composite from 95.8% to 99.8%. Besides, the thermophysical properties of the composite are significantly influenced by the intrinsic conductivity of reinforcement and matrix. It is helpful to reduce the residual pores by deforming and sintering in a liquid-solid co-existent state during the SSPF process. Moreover, the densification mechanism is summarized as four stages: volume packed density reaching peak; alloy powder softening and deforming; alloy powder partial melting and filling into powder gap; cooling and densification.