Material extrusion of high-density SiCp/7075Al composite via a high nitrogen-flowing assisted sintering

Abstract

Material extrusion additive manufacturing of particle-reinforced metal matrix composite (MMC) attracts attention due to the features of uniformly sintered microstructure, easy-to-handle and low cost. However, 3D Al-MMC suffers from poor sinterability due to the stable alumina layer on alloy powder, and difficulty in removing of binders at low temperature. Here, we propose a high nitrogen-flow sintering approach for the thermal debinding and sintering of as-printed SiC particle-reinforced 7075Al (SiCp/7075Al) MMC, without using cumbersome high-vacuum system or pressure-assisted densification. Microcrystalline wax-based granular feedstock was developed based on contact angle testing experiment, which shows typical shear-thinning behavior and satisfactory printing performance. Roles of printing parameters and nitrogen flow rate in the microstructure, phases and mechanical properties of SiCp/7075Al MMC are investigated. Nitrogen flow rate of 2–2.5 L/min accelerates the breaking of oxide film, with the precipitation of intergranular MgAl2O4, Mg2Si phases, and intragranular Al2Cu phases. 3D SiCp/7075Al MMC with a high relative density of 97% and tensile strength of 308 MPa after heat treatment (HT) was achieved based on optimized printing parameters. The availability of high dense structure, combined with controlled microstructure, low-energy demand and low cost, provides a facile route for the application of 3D Al-MMC by material extrusion.