Additive Manufacturing Materials: Fabrication of Aluminum Matrix Composites

This study aims to validate the ability of cryomilling for the production of high-quality aluminum matrix composite (AMC) powder for powder bed fusion (PBF) additive manufacturing (AM). The spectrum of aluminum-based materials available for AM remains limited due to complex melting and solidification dynamics inherent to the process. To overcome these problems, fillers are often added to aluminum matrices to create a class of materials called AMCs that combine the ductility of aluminum with the stiffness of ceramic reinforcements. However, producing particulate composite feedstock powder for PBF that promotes full densification and microstructural homogeneity is nontrivial. Traditional liquid-phase processing through atomization is not suited to produce composite powders as particle segregation discourages composite homogeneity. AM powder production through solid-state mechanical alloying has been studied with limited success, primarily due to poor powder spreadability and inclusion of lubricants in the alloying process. Cryogenic mechanical alloying, termed cryomilling, enhances homogeneity between matrix and reinforcement particles by recurrent fracture and cold welding sans lubricants but remains unexplored for the fabrication of PBF feedstock powder. Herein, a method for producing homogeneous, flowable AMC powder designed for PBF is described in detail. Various compositions, powder masses, and milling times were explored to tune particle morphology, composition, and composite homogeneity. A representative spreading test of cryomilled materials qualitatively indicated that distinct cryomilling parameters may produce powder with comparable spreading characteristics to gas atomized AlSi10Mg, a common PBF feedstock material. Cryomilled AMCs displayed superior Vickers microhardness to unmilled AlSi10Mg powder after compression and sintering. This research provides an indication of cryomilling capabilities to become an effective production method of custom alloy powder for PBF-AM