Enhanced Mechanical Properties and Corrosion Resistance by Minor Gd Alloying with a Hot-Extruded Mg Alloy

Abstract

The microstructure, mechanical properties, and degradation behavior of as-extruded Mg-1.8Zn-0.5Zr-xGd alloys (x=0, 0.5, 1.0, 1.5, 2.0, 2.5 wt%) are investigated. During extrusion, dynamic recrystallization occurs in the alloy and the grain size gradually decreases with increasing Gd content. The mechanical properties and corrosion resistance of the alloys are significantly enhanced by Gd alloying.When the Gd content is 1.5wt%, nanoscale particles of (Mg, Zn) 3 Gd and Mg 2 Zn 11 phases that have a coherent interface with the matrix begin to precipitate out. Under the combined effect of solid solution strengthening, fine grain strengthening and precipitation strengthening, the alloys with 1.5-2.0wt% Gd have a combination of excellent mechanical properties and corrosion resistance. A three-stage corrosion mechanism, including sequential stages from hydroxidation, phosphatization and hydroxidation, to formation-dissolution dynamic equilibrium, is proposed through electrochemical measurements and corroded surface analyses. This extruded Mg-1.8Zn-0.5Zr-(1.5-2.0)Gd alloys can be regarded as the potential candidate for using as biodegradable magnesium implants.