Microstructure and mechanical properties of TiC-modified Al-Zn-Mg-Cu aluminum alloys fabricated by laser powder bed fusion

Abstract

Promoting columnar-to-equiaxed transition (CET) of grain structures is a critical strategy for enhancing the printability and mechanical properties of high-strength aluminum alloys fabricated by laser powder bed fusion (LPBF). One effective method to achieve CET is by enhancing the heterogeneous nucleation of α-Al through the use of in-situ L1₂-Al₃Ti nucleants. Herein, TiC nanoparticles, which are stable at room temperature, are proposed as a safer and more economical alternative to traditional Ti or TiH₂ particles for triggering the formation of in-situ L1₂-Al₃Ti nucleants. The effects of TiC content on the microstructure and tensile properties of LPBF-processed Al-Zn-Mg-Cu aluminum alloys were systematically investigated. The results reveal that TiC nanoparticles effectively induce the formation of potent L1₂-Al₃Ti nucleants and prevent grain growth, facilitating CET, grain refinement, and suppressing cracking without requiring extensive modifications to LPBF processing parameters. The resulting alloys exhibit crack-free, dense, equiaxed, and fine-grained microstructures. The density of the as-built alloys reaches 99.2 %, and the average grain area decreases from 348.3 μm² to 1.7 μm² as the TiC content increases from 0 to 5 wt%. Following conventional T6 heat treatment, the tensile strengths of the LPBF-processed Al-Zn-Mg-Cu aluminum alloys modified with 2.5 wt% TiC are comparable to those of wrought Al-Zn-Mg-Cu aluminum alloys, achieving an ultimate tensile strength (UTS) of 609 MPa, a yield strength (YS) of 537 MPa, and an elongation (El) of 8.3 %, respectively. These findings highlight the potential of TiC nanoparticles as an effective agent for tailoring the microstructure and enhancing the mechanical properties of additively manufactured high-strength aluminum alloys.