Abstract
In the present work, we investigated the governing mechanism of grain refinement in AA3104 Al–Mn alloy made by laser direct energy deposition (DED) additive manufacturing (AM). The microstructure development and phase transformation of DED AM AA3104 were studied by adding different concentrations of Ti, B, Ti–B mixture, and TiB2 particles as grain refiners. The transition from large columnar grains to fine equiaxed grains was achieved by Ti or Ti–B addition, but not by B or TiB2 addition. The study demonstrated that reactive additive manufacturing may be a more effective way to refine grains than directly adding ceramic particles. The formation of Al3Ti plays the most critical role in grain nucleation during DED AM.KeywordsAl-Mn alloysAdditive manufacturingGrain refinementSecond phase particles
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