Influence of post-heat treatment on the microstructure and mechanical properties of Al-Cu-Mg-Zr alloy manufactured by selective laser melting

The properties of modified conventional wrought aluminum alloys cannot be significantly enhanced by normal post-heat treatment in that the fine-grained strengthening, arising from high cooling rate in SLM, is underutilized. In this work, compared with the normal T6 heat treatment, a novel simple direct aging regime was proposed to maintain the grain-boundary strengthening and to utilize the precipitation strengthening of secondary Al3Zr. It was found that a heterogeneous grain structure, which consisted of ultrafine equiaxed (similar to 0.82 mu m) and columnar (similar to 1.80 mu m) grains at the bottom and top of molten pool, respectively, was formed in the SLM processed sample. After direct aging (DA), the ultrafine grains were maintained and a mass of spherical coherent L1(2)-Al3Zr particles with a mean radius of approximately 1.15 nm was precipitated. In contrast, after solution treatment and aging (STA), a significant grain coarsening occurred in the equiaxed grain region. Meanwhile, the coarsening L1(2)-Al3Zr particles, nano-sized S' phases and GPB zones were detected in the STA sample. This subsequently induced that the yield strength of the DA sample (similar to 435 MPa) was higher than that of the STA sample (similar to 402 MPa) owing to the grain boundary strengthening and precipitation strengthening. Both the STA and DA samples exhibited a higher strength than that of the other SLMed Al-Cu-Mg series alloys; this was comparable to that of the wrought AA2024-T6 alloy (similar to 393 MPa). Both the STA and DA samples exhibited a higher strength than that of the other SLMed Al-Cu-Mg series alloys; this was comparable to that of the wrought AA2024-T6 alloy (similar to 393 MPa). (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.

Automated summary

A direct aging regime was proposed to maintain the grain-boundary strengthening and precipitation strengthening in modified conventional wrought aluminum alloys, resulting in a higher yield strength compared to the normal T6 heat treatment. The direct aging treatment preserved the ultrafine grains and precipitated spherical L1(2)-Al3Zr particles, while the solution treatment and aging led to grain coarsening and the presence of coarsening L1(2)-Al3Zr particles, nano-sized S' phases, and GPB zones. Both the direct aging and solution treatment and aging samples exhibited higher strength than other SLMed Al-Cu-Mg series alloys, comparable to the wrought AA2024-T6 alloy.