Role of B4C in the directed energy deposition of aluminum alloy 6061/B4C composite using core-shell powder for crack annihilation, pore mitigation, and grain refinement

Abstract

Despite the high demand for additive manufacturing of high-strength aluminum alloys (60XX and 70XX), high-strength aluminum alloys are one of the most difficult materials to manufacture through metal additive manufacturing (MAM) because of their high laser reflectivity, thermal conductivity, low viscosity, and large solidification range. Thus, MAM products of high-strength aluminum alloys are characterized by pores, cracks, and irregular surface morphology. In the present study, the stable MAM behavior of aluminum matrix composites was achieved by adding B4C reinforcement to the feedstock powder in the form of a novel core-shell powder. The aluminum alloy 6061, which is notorious for its difficulty in MAM, was selected as the matrix. The core-shell B4Cp/6061 MMC powder was prepared for MAM via directed energy deposition (DED). The B4C addition effectively mitigated the formation of cracks, pores, and balling during DED. In addition, the grains were refined, thus preventing anisotropy and improving the mechanical properties. Furthermore, the favorable effect of B4C addition during DED was found to be caused by the formation of AlB2 during solidification. These findings provide a basic understanding of the promising potential of MMCs fabricated by MAM.