Effect of Microstructure Features of Rapidly Solidified Ribbon-Consolidated Mg-Zn-RE Alloys on Mechanical and Corrosion Performance

Thanks to the excellent strength-to-weight ratio Mg alloys have been attracting considerable attention as a structural material for engineering applications and the transportation (airplane and automobile) industry. Moreover, the biocompatibility of Mg motivates their further development as a bio-implant material, e.g., for orthopedic implants, screws or/and cardiovascular stents. Therefore, there is a need for the development of Mg alloys with enhanced properties with respect to a particular use.<br/>The Mg-Zn-RE (rare earth) alloys prepared by the consolidation of rapidly solidified (RS) ribbons are characterized by complex microstructure with elongated worked and dynamically recrystallized grains with an overall average grain size of about 800 nm and weak basal texture. Using a low amount of alloying elements (up to 2at.%) results in the formation of solute segregated Zn- and Y-rich stacking faults (SFs). In order to optimize the performance of alloys, the influence of both amount of the alloying elements (between 1-2 at.% of Zn and Y) and the metal flow rate during the consolidation of RS ribbons (via extrusion) on the microstructure and resulting mechanical properties has been elucidated. The alloy with optimal values of tensile yield strength and elongation of 362 MPa and 18.9 %, respectively, has been subjected to corrosion performance testing. Corrosion behavior of RS ribbons-consolidated alloy is compared with one of an extruded alloy of the same composition having a larger grain size of α-Mg (9 µm) and wavy fractures of long period stacking ordered (LPSO) phase (10 µm). For evaluation of corrosion resistance, besides common electrochemical methods, such as hydrogen release, electrochemical impedance spectroscopy, cathodic polarization, an<i> in-situ</i> acoustic emission technique was employed during immersion of the samples in NaCl solution. The tensile properties and corrosion performance were correlated to the microstructure features, such as dispersion of SFs and LPSO phase, grain size, distribution of internal strain via KAM analysis. Inhomogeneous distribution of internal strain in the complex microstructure was found to be of key importance for the performance of dilute RS ribbons-consolidated alloys.