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 μm for the as-extruded sample and to 3.5 μm 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.