Microstructural evolution and mechanical behavior in additively manufactured A205 alloy: as-built and heat-treated conditions

A TiB2 nanoparticle-inoculated high-strength Al-Cu-Mg-Ag-(Ti) alloy known as A205 was employed to manufacture horizontal bars through laser powder bed fusion (LPBF) and post-processed with T7 heat treatment. The microstructural characteristics of both the fabricated and heat-treated samples were assessed using various advanced electron microscopy techniques. The findings indicated that increased thermal supercooling caused by laser powder-bed fusion induced the activation of a multitude of TiB2 inoculants facilitating heterogeneous nucleation. This process reduced the average grain size within the as-built samples, reaching a refinement level that allows the manufactured materials to be classified as ultra-fine grain materials. The application of T7 heat treatment, encompassing solution annealing and subsequent artificial aging, resulted in uneven grain growth and the formation of diverse strengthening elements within the microstructure including GP zones, θ”, θ’, and Ω phases. This intricate microstructural evolution had a notable impact on the mechanical properties. In the heat-treated samples, discontinuous yielding was no longer observed, and substantial enhancements in ultimate tensile strength of over 75 % were observed. However, these strength gains were accompanied by a reduction in ductility highlighting a trade-off between increased strength and decreased ductility. The significant decline in ductility observed in the heat-treated (HTed) samples (∼74 %) can be attributed to the emergence of intermetallic compounds (IMCs) within the precipitation-free zones (PFZs) along the grain boundaries.