Effect of heat treatment on microstructure and mechanical properties of AA2219 Al-Cu alloy processed by Laser Powder Bed Fusion

This study investigated the Laser Powder Bed Fusion (LPBF) processing and heat treatment response of the Al-Cu alloy AA2219. Fully dense samples with a relative density of 99.90 ± 0.05% were produced. Age hardening response was studied via T5 and T6 heat treatments with artificial aging up to 24 hrs. Transmission electron microscopy (TEM) analysis of the as-built (AB), T5 and T6 samples were conducted to quantify the distribution of Cu in the system in the various phases (solid solution, Θ-Al 2 Cu, Θ′ and Θ″) to understand the strengthening response. The mechanical properties were assessed for the AB sample and the peak-aged T5 and T6 samples. Microhardness increased from 85 ± 4 HV0.2 in the AB condition to 101 ± 3 HV0.2 and 145 ± 2 HV0.2 for T5 and T6 conditions, respectively. The yield strength (YS), ultimate tensile strength (UTS), and elongation at fracture of the AB and T5 samples were 94 ± 6 MPa, 288 ± 6 MPa, 8.7 ± 1.5% and 98 ± 8 MPa, 295 ± 8 MPa, 6.0 ± 0.7%, respectively, which indicates that the T5 heat treatment had no significant influence on these properties. T6 heat treatment showed a significant increase in YS (266 ± 5 MPa), UTS (411 ± 6 MPa) and elongation at fracture (12.4 ± 2.7%). The improvement in microhardness and tensile strength from AB to T5 and T6 arises from the distribution of fine θ″ and θ′ precipitates, which impedes dislocation motion. The energy of initiation ( E i ) of the AB, T5 and T6 samples were 4.5 J, 3.6 J and 4.2 J, respectively. The energy of propagation ( E p ) exhibited a declining trend across AB, T5, and T6 conditions, measuring 6.5 J, 4.9 J, and 3.9 J, respectively. This variation in behavior is attributed to a shift in fracture mechanism, from activation of a single slip system during tensile loading, to activation of multiple slip systems under impact loading. • Crack free AA2219 can be fabricated by LPBF without platform heating. • T6 strengthening is more sensitive to aging temperature than T5 treatment. • T6 treated LPBF AA2219 exhibit superior tensile strength and ductility. • Heat treatment lowers the impact energy due to precipitate formation. • T5 and T6 samples have a similar response under impact loading.