Microstructure and corrosion behavior of the solution-treated Mg-1.8Zn-1.74Gd-0.5Y-0.4Zr (wt%) alloy were studied. The results of microstructure indicated that the second phases of as-cast alloy was mainly comprised of Mg₁₂Zn(Gd,Y) phase, Mg₃Zn₃(Gd,Y)₂ phase and (Mg,Zn)₃(Gd,Y) phase. After solution treatment process, the second phase gradually dissolved into the matrix, and the grain size increased. The effect of microgalvanic corrosion between α-Mg matrix and second phase was also improved. At the range of 470~510 °C solution treatment temperature, the corrosion resistance of the samples increases at first and then decreases slightly at 510 °C. All the solution-treated Mg-Zn-Gd-Y-Zr samples exhibit better corrosion resistance in comparison with as-cast sample. The existence form of the remaining phase affects the morphology of the corroded surface that relatively complete dissolution with homogeneous microstructure makes the sample more effective to obtain uniform corrosion form. The optimum temperature for solution treatment is 490 °C, which shows a much better corrosion resistance and uniform corrosion form after soaking for a long time.

The effects of solution treatment on microstructure, mechanical properties and corrosion behavior of Mg-2Zn-1Y-0.5Zr alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), confocal laser scanning microscope (CLSM), X-ray diffraction (XRD), tensile tests, electrochemical test and immersion test. The results indicated that the as-cast alloy was comprised of an equiaxed α-Mg matrix, I-phase, W-phase and MgZn2 phase. After solution treatment at different temperatures, the second phase gradually dissolved into the magnesium matrix, and the grain size of the alloy increased to different degrees. The alloy solution-treated at 420 ℃ for 10 h had better mechanical properties, and its tensile strength, yield strength and elongation were 195.0 ± 5.4 MPa, 97.3 ± 1.9 MPa and 25.8 ± 0.4%, respectively. The alloy solution-treated at 440 ℃ for 10 h had better corrosion resistance and its corrosion rate was 0.304 ± 0.021 mm/y. The best mechanical properties and corrosion resistance can be obtained by balancing the volume fraction of the second phase and grain size. The alloy after solution-treated at 440 ℃ for 10 h has the best comprehensive properties.

In this investigation, the effects of different annealing temperatures (180, 200, 220, 240, 260, and 280 °C) on the microstructure evolution and properties of an extruded Mg–2.0Zn–1.0Y–0.5Zr (wt%) magnesium alloys were determined. Optical microscopy (OM), scanning electron microscopy (SEM), immersion corrosion, electrochemical corrosion experiments, and tensile testing were performed. Research has found that combining hot extrusion with subsequent low-temperature annealing significantly improves the strength, plasticity, and corrosion resistance of alloys due to grain refinement and a reduced dislocation density. The alloy was completely recrystallized at an annealing temperature of 240 °C for 4 h after solid solution extrusion, and the grains were fine and uniform, demonstrating the best comprehensive properties. Its corrosion rate, ultimate tensile strength, yield strength, and elongation were 0.454 ± 0.023 mm/y, 346.7 ± 8.9 MPa, 292.4 ± 6.9 MPa, and 19.0 ± 0.4%, respectively. The corrosion mechanism of the specimens under extruded and annealed conditions was analyzed. After annealing at 240 °C for 4 h, the dislocation and bimodal grain structure of the samples were almost eliminated, resulting in uniform and fine grains, which were conducive to the formation of a more uniform and denser oxide film, thus improving the corrosion resistance of the alloy.