Microstructure, mechanical properties, and fatigue performance of a PBF-LB Al2139ZrTi alloy

Abstract

This study investigates the microstructure, tensile, and fatigue behavior of post-aged powder bed fused-laser beam (PBF-LB) Al2139ZrTi alloy, developed by EOS North America. The microstructure exhibits an equiaxed grain structure with an average grain size of approximately 1.5 µm and lacks any strong crystallographic texture. It also contains a dense dispersion of fine, uniformly distributed precipitates including: (i) Al₃(Zr,Ti) dispersoids with L1₂-type structure, acting as semi-coherent nucleation sites that contribute to grain refinement; (ii) a unique Al₃(Zr,Ti) plate-like phase, further confirming Zr–Ti-driven modification of precipitation pathways; (iii) Al(CuFeMn) and Al(MnCu) intermetallics, notably Al₇Cu₂ (Fe,Mn) and Al₂₀Cu₂Mn₃(T-phase), and (iv) Mg oxides, pointing to minor oxidation during processing. Notably, Al₂Cu-based θ′ and Ω phases are sparse, with only coarse θ-phase particles (∼0.5–1 µm) at grain boundaries and fine plate-like Ω-phase (∼tens of nm thick) along the [100] zone axis. Mechanical properties were evaluated via tensile testing, yielding ∼ 470 MPa yield stress (YS), ∼570 MPa ultimate tensile strength (UTS), and ∼ 6.5 % elongation. Conventional (servo-hydraulic) and ultrasonic fatigue tests were performed to cover high cycle and very high cycle fatigue responses spanning up to 10⁹ cycles. Fractographic analyses, including optical and electron microscopy techniques, were carried out to quantify the crack initiation mechanisms in the mentioned regimes.