The role of Ti addition in AA6061 fabricated by LPBF and its influence on mechanical and thermal properties

Grain refinement is one of the most efficient strategies to mitigate hot cracking in additively manufactured aluminum alloys (AAs), achieved through the addition of potent nucleates or solutes. While prior studies have demonstrated success in suppressing hot cracks in 6xxx series AAs fabricated by laser powder bed fusion (LPBF), the combined effects of grain refiners and heat treatment on microstructure, mechanical, and thermal properties remain insufficiently explored. In this work, Ti was deliberately selected as a peritectic-forming solute due to its strong segregation tendency in Al and the low lattice misfit of Al 3 Ti with the Al matrix. Primary L1 2 -Al 3 Ti particles formed predominantly in the fine equiaxed grain regions near melt-pool boundaries, serving as heterogeneous nucleation sites and effectively refining grains in AA6061. Grain size decreased with increasing Ti content and growth restriction factor ( Q ), though the relationship between grain size and 1/Q was non-linear. Post-T6 heat treatment induced partial recrystallization, enhanced thermal conductivity, and eliminated Lüders and Portevin–Le Chatelier (PLC) bands in stress–strain curves of Ti-modified AA6061. Finally, Kou's criterion and freezing-range-based criteria were found inadequate for evaluating hot cracking susceptibility in Ti-modified AA6061 under LPBF, indicating that grain-refinement effects should be explicitly considered in future RDG-based or other crack-susceptibility models.