Corrosion Resistance Improvement of an Extruded Mg-Gd-Y-Zn-Zr-Ca via Aging Treatment

The effects of aging treatment on corrosion properties of an extruded Mg-8.9Gd-2.8Y-1.8Zn-0.4Zr-0.2Ca (wt.%) alloy were investigated. The as-extruded alloy was consisted of un-dynamically recrystallized region containing lamellar long period stacking ordered (LPSO) phase and block-shaped LPSO phase, finely recrystallized grains and small amounts of Mg-RE phase. After aging treatment, part of lamellar LPSO phases was dissolved into the matrix and replaced by recrystallized grains. The size of recrystallized grain was increased from 1.8 mu m for the as-extruded sample and to 3.5 mu m for the peak-aged sample. Corrosion tests indicated that aging treatment effectively improved the corrosion resistance of the as-extruded Mg-8.9Gd-2.8Y-1.8Zn-0.4Zr-0.2Ca (wt.%) alloy. The lamellar LPSO phases with a low potential were preferentially corroded, and the homogeneous microstructure of the peak-aged sample effectively reduced the possibility of micro-galvanic corrosion. Hence, the peak-aged sample with a more homogeneous microstructure and small amount of lamellar LPSO phase showed a better corrosion resistance.

Automated summary

The study showed that aging treatment significantly improved the corrosion resistance of the extruded Mg-8.9Gd-2.8Y-1.8Zn-0.4Zr-0.2Ca alloy by dissolving part of the lamellar LPSO phases and increasing the size of recrystallized grains, thereby reducing the possibility of micro-galvanic corrosion. The peak-aged sample with a more homogeneous microstructure and small amount of lamellar LPSO phase exhibited the best corrosion resistance.