Enhanced microstructure homogeneity of rare earth magnesium alloy under electropulsing

Abstract

The second phases at grain boundaries including block-shaped long-period stacking ordered (LPSO) phases and bright W phases are the chief culprits damage the deformability of as cast Mg-Gd-Y-Zn-Zr magnesium alloy. The industry homogenization (520 °C/12 h) is indispensable for microstructure homogeneity, but has the disadvantages including long period, low efficiency and high oxidation burning rate. Here it was found that the microstructure homogeneity can be rapidly performed under electropulsing at a relative low temperature of 422 °C, and the holding time is only 10 min. The block-shaped LPSO phases and bright W phases at the grain boundaries were selectively dissolved and decomposed. The volume fraction of the second phases was reduced from 17 % to 12 %, indicating that the electropulsing is a more efficient method. Meanwhile, the elongation was enhanced to 6.2 %, which is higher than that of the traditional industry homogenized sample. The numerical calculation results present that the high current density regions at the tips of lamellar LPSO phases (near the grain boundaries) are the key factors to accelerate the solute elements exchange, so as to complete the fast microstructure homogeneity enhancement.

Keywords

• Mg-13Gd-4Y-2Zn-0.5Zr magnesium alloy
• Electropulsing
• LPSO phase
• Mechanical properties