Enhanced thermal conductive 3D-SiC/Al-Si-Mg interpenetrating composites fabricated by pressureless infiltration

Abstract

A high thermal conductive 3D-SiC/Al-Si-Mg interpenetrating composite (IPC) with three dimensional mutually interpenetrated structure was fabricated by mold-forming and pressureless infiltration method. Al-15Si-10Mg was used as the infiltration aluminum alloy. The obtained composite was treated with a T6 procedure. The composed phases, microstructure, thermal conductivity, mechanical strength and fractography of the prepared 3D-SiC/Al-Si-Mg IPC were either analyzed or measured with X-ray diffraction (XRD), optical metallography, laser thermal conductivity instrument, universal testing machine, field emission electron scanning microscopy (SEM) with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and etc. The results showed that both SiC ceramic and aluminum alloy phases distribute evenly and form a three-dimensional mutually interpenetrated structure in the obtained IPC. No clear brittle and harmful Al₄C₃ phase was found in the composite. The obtained IPC contains a SiC volume fraction of 67 vol% and has the properties of a density of 3.02 g/cm², a thermal conductivity of 233.6 W/(m °C), a thermal expansion coefficient (RT~300 °C) of 7.03×10⁻⁶/°C and a bending strength of 288 MPa.

Introduction

The thermo-physical properties and mechanical properties of SiC/Al composites can be tailored to meet the dual requirements of structure (supporter) and function (heat transfer) as being electronic packaging materials [1], [2], [3]. Furthermore, SiC/Al composite has high specific strength and good size stability, which make it having unsubstitutable superiority in the field of electronic packaging and potential wide applications in the airplane, airspace, automobile and others [4], [5], [6], [7], [8], [9], [10]. Among many manufacturing methods in making SiC/Al composites, pressureless infiltration method has the advantages of a relatively simple technology and a low cost. However, the thermal conductivity of SiC/Al composites manufactured using this method reported so far is usually low with a value in the range of 120–170 W/(m °C) [11], [12], [13], [14]. The main reason for this is that in order to depress the forming of harmful interfacial reaction product Al₄C₃ and to improve the wettability between SiC and Al liquid, the SiC powders or preforms are oxidized to form a layer of SiO₂ on the SiC surface [15], [16]. The SiO₂ layer has a lower thermal conductivity which acts as the heat barrier to the transport of electrons and phonons between SiC and Al phases as well as among SiC powders, resulting in the enhancement of interfacial thermal resistance which lowers the thermal conductivity of composites. Moreover, SiC/Al composites made with oxidized SiC particles form usually particle reinforced SiC_p/Al composites, i.e., SiC particles are discretely distributed in a continuous Al matrix. By contrast, 3D-SiC/Al IPC has a three-dimensional mutually interpenetrated structure and possesses a high thermal conductivity, because both SiC and Al component phases interlinked continuously supplying channels for heat transfer [4], [17], [18]. However, few reports on the preparation of 3D-SiC/Al IPC by pressureless infiltration method have been found in the literature so far, hence further study on this subject including the preparation technology and properties of 3D-SiC/Al IPC is necessary.

The purpose of this study is to fabricate a high conductive 3D-SiC/Al-Si-Mg IPC using pressureless infiltration method. SiC powders or preforms are not oxidized in order to avoid the negative effect of SiO₂ interfacial layer to the thermal conductivity of composite and to make the composite have properties of higher thermal conductivity, lower thermal expansion coefficient and sufficient strength.