Abstract Scope |
Wrought aluminum alloys, particularly those exhibiting high strength, are already seeing extensive use in aerospace and automotive applications given their high strength-to-weight ratio. Additive manufacturing (AM) of these alloys has become more common in meeting demands of these industries while overcoming the limitations of conventional manufacturing processes. However, many alloys of this class possess a propensity for solidification cracking, resulting in reduced ductility and tensile strength, which tends to make them unsuitable for welding and AM processes. In addition, higher stiffness and more robust high-temperature properties are desirable if these alloys are intended for aerospace applications. Addition of ceramic particulates to an Al alloy to form a metal matrix composite (MMC) has been shown to both mitigate solidification cracking and achieve these desired properties. For enhanced solidification cracking resistance and uniform mechanical properties, the reinforcement phase must be uniformly distributed and possess a small mean diameter. Reaction synthesis can be used to form ceramic or intermetallic products that serve as the reinforcing phase in an MMC. Reaction synthesis is also expected to address the poor wettability of the ceramic phase through the presence of much higher temperatures during the reaction.
In this work, aluminum-based reactive additive manufacturing (RAM) feedstocks are employed in welding, laser powder-bed fusion (PBF), and electron beam freeform fabrication (EBF3) processes to examine the effect of feedstock composition and precipitate morphology on deposit microstructure and mechanical properties. The RAM feedstocks were characterized using scanning electron microscopy and particle size analysis. X-ray diffraction confirmed the presence of ceramic and intermetallic secondary phases in builds that used the RAM feedstock. Light optical microscopy and electron back-scatter diffraction were used to examine texturing and the extent of grain refinement among the various feedstock compositions and the different solidification processes. ASTM subsize tensile and Charpy specimens were machined from each build to measure the tensile strength and impact energy of materials produced by each process. |