Effect of Heat Treatment on Microstructure and Mechanical Properties of Laser Powder Bed Fused ZrO2-GNPs/2024Al Composites

Abstract:

1wt%ZrO₂-0.2wt%GNPs/2024Al composites were prepared by laser powder bed fusion (LPBF) process. The phase composition and microstructure evolution of the as-deposited and heat-treated (475 ℃ solution treatment for 1 h+140 ℃ aging treatment for 12 h) composites were characterized to reveal the changes in mechanical properties. Results show that compared with that of the as-deposited samples, the microhardness of the composites is maximally enhanced under the heat treatment regime of 475 ℃/1 h+140 ℃/12 h. The second phases precipitated in the samples are mainly in the form of Al₂Cu strips and Al₂CuMg plates. The tensile strength and yield strength are increased from 382 MPa and 269 MPa to 624 MPa and 522 MPa, respectively, but the elongation is decreased from 16% to 5.6%. The strength enhancement is mainly attributed to the dislocation and load transfer strengthening effects caused by heat treatment, which has a much greater influence than the coarsening of the second phase and grain growth caused by heat treatment. The decrease in plasticity is mainly due to the coarse Al₂Cu and Al₂CuMg second phases which are prone to fracture and detach from the Al matrix, promoting to the premature formation of local shear bands and voids.