热处理对激光粉末床熔融ZrO2-GNPs/2024Al复合材料显微组织及力学性能的影响

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

摘要:

采用激光粉末床熔融（laser powder bed fusion，LPBF）工艺制备1wt%ZrO₂-0.2wt%GNPs/2024Al复合材料，研究沉积态及热处理（475 ℃固溶处理1 h+140 ℃时效处理12 h）后复合材料的物相组成、微观组织的演变并揭示材料力学性能的变化。相比沉积态的样品，在475 ℃/1 h+140 ℃/12 h热处理制度下材料显微硬度提升最大，试样中析出的第二相主要为条状的Al₂Cu和方状的Al₂CuMg，抗拉强度和屈服强度分别从382和269 MPa提高到624和522 MPa，但延伸率从16%降至5.6%。强度提升主要归因于热处理引起的位错和载荷传递强化效应，其影响远大于热处理导致的第二相粗化和晶粒增大效应。而塑性下降主要是由于粗大的Al₂Cu和Al₂CuMg第二相易于断裂，且易于从Al基体中脱离，从而导致局部剪切带和空隙的过早形成。

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.