Microstructure and corrosion behavior of as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys (x=4, 8, 12)
(National Engineering Research Center of Light Alloy Net Forming and State Key Laboratory of Metal Matrix Composite, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)
Abstract: The microstructure and corrosion behavior of the as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys (x=4, 8, 12, wt.%) were studied. The results show that as the Li content increases from 4% to 12%, the matrix transfers from single α-Mg phase, (α-Mg+β-Li) dual phase to single β-Li phase. A mixed corrosion feature of intergranular corrosion and pitting corrosion occurs in the Mg-4Li-3Al-2Zn-0.5Y and Mg-12Li-3Al-2Zn-0.5Y alloys. The former is related to the precipitated AlLi phase along the grain boundaries, and the latter is related to the high potential difference between the second phase and the matrix. The corrosion resistance of the as-extruded alloys is better than that of the as-homogenized alloys. The superior corrosion resistance of the as-extruded Mg-8Li-3Al- 2Zn-0.5Y alloy with the lowest corrosion rate (PW=(0.63±0.26) mm/a) is attributed to the more uniform distribution of second phases, the protective α-Mg phase via sacrificing the β-Li phase and the relatively integrated oxide film.
Key words: Mg-xLi-3Al-2Zn-0.5Y alloys; microstructure; corrosion behavior; homogenization; extrusion; second phase; oxide film