An Opposite Tendency of Mechanical Properties and Corrosion Resistance of a High-Strength Al-5024 Alloy Processed by Laser Powder Bed Fusion

Abstract

Laser Powder Bed Fusion (LPBF) manufactured Al-5024 alloy has gained worldwide interest due to its ability to fabricate high-performance complex components. This work focuses on quantitative characterization and synergic optimization of the microhardness, tensile strength, and corrosion resistance of an LPBF manufactured Al-5024 alloy by optimization of heat treatment parameters. The effect of the isothermal heat treatment (IHT) process on the microstructure evolution, mechanical properties, and electrochemical properties of an LPBF-processed Al–4.2Mg–0.4Sc-0.2Zr alloy was systematically revealed. Results showed that superior tensile strength of 506.7 ± 10.4 MPa combined with inferior corrosion resistance was simultaneously obtained at a peak-aging condition. Based on microstructure observations by electron microscopy in backscattered mode (BSE) and transmission electron microscopy (TEM), the enhanced mechanical properties were attributed to the generation of a high number density (3.8 × 109/mm2) of grain interior precipitates, while the reduced corrosion resistance was related to the massive Al3(Sc,Zr) precipitates generated along grain boundaries. As aging time further increased, the size and spacing of the precipitates were increased, which blocked the corrosion path along grain boundaries and led to a reduction of mechanical properties and an enhancement of corrosion resistance. Unlike the expected synergistic improvement in mechanical properties and corrosion resistance, an opposite evolution tendency of mechanical properties and corrosion resistance of LPBF-processed Al-5024 alloy during heat treatment was revealed in this paper, and its intrinsic mechanism is further analyzed based on microstructure characterization.