In-situ aging treatment by preheating to obtain high-strength ZK60 Mg alloy processed by laser powder bed fusion

Abstract

In this study, a ZK60 Mg alloy fabricated by laser powder bed fusion (LPBF) is subjected to in-situ aging treatment by preheating the substrate. The effects of preheating temperature on the microstructure, mechanical properties, and corrosion resistance of the LPBF-processed ZK60 alloy are systematically analyzed. The results show that at the preheating temperatures of 35, 90, and 180 °C, the average grain size of the samples does not change much, ranging between 7.0 and 8.2 μm. As the preheating temperature increases, the mechanical properties of the alloy increase. The specimens treated at a preheating temperature of 180 °C exhibit a yield strength (YS) of 201 ± 5 MPa, ultimate tensile strength (UTS) of 291 ± 7 MPa, and elongation (EL) of 14.7 ± 0.8%. This is attributed to the precipitation of a large amount of β’ 1 phase in the alloy during the aging state in the LPBF process. However, the corrosion resistance first improves and then deteriorates with the increase in the preheating temperature. Under a preheating temperature of 90 °C, the corrosion resistance is improved due to the reduction in the galvanic corrosion area by the precipitated phases. When the preheating temperature is increased to 180 °C, the precipitated phases and α-Mg form a large number of microgalvanic cells, which increases the active center for corrosion and deteriorates the corrosion resistance. These findings indicate that the desired mechanical properties and corrosion resistance of the LPBF-processed ZK60 alloy can be obtained by selecting an appropriate preheating temperature. • The cracks significantly reduce in LPBF-processed ZK60 alloy by substrate preheating. • The mechanical properties increase with increasing preheating temperature. • The corrosion resistance first improves and then deteriorates. • β’ 1 phase is beneficial to mechanical properties but deteriorates corrosion resistance.