Effect of Cu micro-alloying on the microstructure, mechanical and corrosion properties of Mg-Gd-Y-Zn based alloy applied as plugging tools

Abstract

Dissolvable functional magnesium alloys are attracting strong attention due to the prominent advantages of high strength and suitable dissolution rate. Here, the effect of Cu micro-alloying (0, 0.4, 0.8 wt%) on the microstructure, mechanical and corrosion properties of Mg-9.5Gd-2.7Y-0.9Zn alloys are investigated. With the increase of Cu contents, the block 14 H long-period stacking ordered (LPSO) phase gradually increases, which promotes the nucleation of dynamic recrystallized (DRXed) grains. However, the migration of the sub-structure is inhibited caused by the plate LPSO phase and the growth of DRXed grains is suppressed. Eventually, the grain size of DRXed grains decreased. The alloy with 0.8 wt% Cu obtains higher yield strength compared with Cu-free alloys, which is mainly ascribed to multiple strengthening contributions containing second phase, dislocation, grain boundary and solid solution. Due to the potential difference between the LPSO phase and the Mg matrix in the investigated alloys, the LPSO phase acts as cathodic to accelerate corrosion. The 0.8Cu alloy exhibits the highest corrosion rate, which is the synergistic effect of the second phase (its larger volta potential compared with 0Cu and its higher fraction of LPSO phase), dislocation density, grain size and crystal orientation. Ultimately, the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu alloy exhibits an ultimate tensile strength of 380 MPa, tensile yield strength of 331 MPa, and decent corrosion rate (16.8 mg·cm−2·h−1 at 93 °C in 3 wt% KCl solution). This work strengthens understanding the Cu role in designing high-strength dissolvable Mg-RE alloys.