Analysing the combined effect of crystallographic orientation and grain refinement on mechanical properties and corrosion behaviour of ECAPed ZE41 Mg alloy

Abstract

Two step equal channel angular pressing carried out on as cast ZE41 Mg alloy resulted in a remarkable grain refinement. As compared to grain size of 46 µm in as cast sample, refinement upto 2.5 µm was achieved after 8th pass equal channel angular pressing (ECAP). The combined effect of crystallographic orientation and grain refinement was investigated by analysing the mechanical properties and corrosion behaviour of ZE41 Mg alloy using electron back scattered diffraction (EBSD). The first stage comprises of 1st, 2nd, 3rd and 4th passes at a processing temperature of 300 °C while the 5th, 6th, 7th and 8th passes were ECAPed at 275 °C in second stage. The mechanical properties of ZE41 Mg 158 yield tensile strength (YTS), 230 ultimate tensile strength (UTS) and 7% elongation in as cast condition is enhanced to 236 YTS, 295 UTS and 19.76%, respectively, after first stage ECAP. The yield tensile strength deteriorated due to the effect of texture predominating grain refinement during the second stage ECAP. The corrosion resistance of ZE41 Mg was significantly enhanced by ECAP and is inferred from electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation results .The role of microstructure was minimal on corrosion behaviour of ZE41 Mg due to extra resistance when tested in 0 M NaCl. However, the influence of grain refinement greatly influenced the improvement in corrosion resistance of ZE41 Mg rather than crystallographic orientation observed from EBSD. In contrast, the crystallographic orientation predominated the effect of grain refinement during ZE41 Mg corrosion in chloride containing (0.1 M and 1 M NaCl) solutions. From the observation of results it is found that equal channel angular pressing has the dual advantage of improving mechanical properties and corrosion resistance of ZE41 Mg alloy. © 2020