Post-heat treatment of laser powder bed fusion fabricated Al–La–Mg–Mn alloy: On intermetallic morphology control and strength-ductility balance

Abstract

In this study, a newly developed Al–La–Mg–Mn alloy was subjected to solution heat treatment for the first time. During the solution heat treatment at 500 ℃, the continuous network Al11La3 intermetallics were transformed into a discontinuous granular form. Ultrafine intermetallics (∼0.20 µm) were achieved via multi-point spheroidization with the aid of endogenous nanoprecipitates. Of note, the intragranular intermetallics were inert to coarsening, while the intergranular intermetallics grew gradually to ∼0.58 µm within 6 h. Compared to the as-printed alloy (UTS ∼588 MPa, Elongation ∼6.4%), the solution-treated alloy at 500 ℃ for 1 h (UTS ∼477 MPa, Elongation ∼14.3%) demonstrated a remarkable improvement in ductility, with a 123% increase, despite a modest decrease of 19% in strength, thereby balancing the strength-ductility. The limited decline in strength is primarily attributed to the high-content solute Mg atoms and thermally stable intragranular intermetallics. Interestingly, the mechanical properties were independent of the holding times at 500 ℃, despite the coarsening of intergranular intermetallics. This is mainly due to the optimization of intermetallics’ scale distribution, which tailors and equalizes the stress distribution between the grain boundary and interior, as well as between the melt pool boundary and interior during deformation. These findings provide the first insight into the effect of post-heat treatment on the intermetallic evolution and mechanical properties of LPBF Al–(La, Ce) alloys.