Effect of laser additive manufacturing on the microstructure and mechanical properties of TiB2 reinforced Al-Cu matrix composite

Abstract

Understanding the effect of reinforcements on microstructure evolution and strengthening mechanism in aluminum matrix is crucial for development of good performance aluminum matrix composites (AMCs) prepared by laser additive manufacturing (LAM). In this work, the roles of submicron-TiB2 particles in the grain morphological evolution, mechanical properties and corresponding strengthening mechanism of the 2024Al matrix processed by laser directed energy deposition (L-DED) and laser powder bed fusion (L-PBF) were comparable investigated. The microstructure of L-DED processed TiB2p/2024Al composite consists of equiaxed grains, instead of the coarse columnar grains in L-DED prepared 2024Al alloy. While only the refinement of columnar grains was observed in the L-PBF processed similar composite sample. Combining with the thermal simulation results and Hunt criterion, the solidification conditions of the molten pool during L-DED process facilitate the formation of Al-Ti layer between TiB2 and Al matrix, which promotes the columnar to equiaxed transition (CET) of α-Al grains by increasing the nuclei density (N0). The as-fabricated 3 wt %-TiB2p/2024Al composites, no matter prepared by L-DED or L-PBF, exhibited simultaneously enhanced strength and plasticity (elongation) due to the grain refinement. The grain boundary strengthening, dislocation strengthening and load transfer strengthening should be responsible for the increase of 79% in yield strength (YS) of L-DEDed TiB2p/2024Al sample. While the increment of YS for L-PBFed composite sample is 15%.