Effect of I-phase morphology and microstructure transformation in biomedical Mg-3Zn-1Mn-1Y alloys on vitro degradation behavior in dynamic simulated body fluid

The corrosion mechanism of as-cast, heat-treated (H400) and extruded (E30, E60, E90) Mg-3Zn-1Mn-1Y alloys with different microstructure is investigated by scan electron microscope (SEM), scan Kelvin probe force microscope (SKPFM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance analysis and immersion experiments equipped with a dynamic corrosion device. The relevant results are as follows: continuously strip-like I-phase (Mg 3 Zn 6 Y) in as-cast alloy distributed along the grain boundary played a significant obstacle impact during corrosion, whereas this capability is weakened after heat treatment and large plastic extrusion deformation. However, extrusion deformation significantly improved alloy corrosion performance, the extruded E30 alloy performed superior anti-corrosion behavior among the three extruded alloys owing to the smaller potential difference between I-phase (2.59 V) and DRXed (2.51 V) or un-DRXed (2.54 V) grains. In addition, the corrosion obstacle effect of grains boundaries (the grain boundary has higher potential than the Mg substrate), dense corrosion products film protection (isolate the substrate from contact with SBF) and typical basal texture (lower reactivity of base atoms) have great influence on corrosion behavior.