Effect of Mn addition on the microstructure, mechanical properties and corrosion resistance of a biodegradable Mg–Gd–Zn alloy

Abstract

Abstract The effect of 0.5 and 1\xa0wt% Mn additions on the microstructure, mechanical properties, and biocorrosion resistance of an extruded Mg–3Gd–1Zn (GZ31) alloy was investigated. Mn addition refined the grain structure so that the grain size decreased from 3.7\xa0μm for the GZ31 alloy, to 2.3\xa0μm for GZ31–1Mn alloy. Hardness measurements and shear punch tests (SPT) revealed that by adding 1\xa0wt% Mn, the hardness, shear yield stress (SYS) and ultimate shear strength (USS) increased from 61 to 66 Hv, 102.0 to 128.5\xa0MPa, and 142.8 to 152.4\xa0MPa, respectively. The main mechanisms responsible for the improvement of mechanical properties were grain refinement and higher volume fraction of the second phase particles formed by Mn addition. Electrochemical impedance spectroscopy showed that the addition of 1\xa0wt% Mn increased the overall corrosion resistance from about 515.4\xa0Ω\xa0cm2 to 5883.6\xa0Ω\xa0cm2. In addition, initiation of the inductive loop in the Nyquist diagrams of the Mn-containing alloys, in the lower frequencies in comparison to the base alloy, can be a sign of retarding the onset of pitting corrosion. The improved corrosion resistance of these alloys was due to the refined microstructure and formation of a more stable protective layer on the surface.