Selective laser melting of elemental aluminum silicon mixtures

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Roberts, Christopher Eli

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Additive manufacturing technologies have generated increasing interest by public, government, and academic institutions alike. While past research has increased part quality, build speed, and process reliability, there remains few materials which can be processed through selective laser melting (SLM). Historically, metal feedstock for powder bed fusion processes have been pre-alloyed, near-eutectic grades similar to traditional casting alloys. This thesis discusses an alternative processing route utilizing elemental mixtures for off-eutectic, difficult-to-processes alloys which exhibit a large freezing range and solidification shrinkage such as that found in many wrought aluminum alloys. One such alloy is aluminum 6061. This material is of great commercial interest due to its widespread use within the traditional manufacturing industry, successful prior certification in aerospace industries, and good mechanical properties. Since AA6061 consists of multiple elements, a representative system of aluminum and silicon was utilized for consideration in this thesis. A powder feedstock of commercially pure aluminum and silicon was prepared and processed through SLM. Samples were then heat treated to homogenize the silicon aluminum matrix. Metallographic analysis was performed throughout the experiment to determine the underlying materials processes. Dense parts without solidification cracking were produced and silicon dissolution into the aluminum matrix was verified using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The combined-powder process that is outlined could be expanded to other material systems which are not compatible with current additive manufacturing technologies. An overview of the theory behind the use of elemental mixtures as well as the results from the aluminum silicon (Al-Si) mixture are presented. Future work needed to be accomplished and potential challenges associated with this processing route are also discussed.


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