Effect of Extrusion Temperature and Extrusion Ratio on Microstructure and Biodegradation Behavior of Mg-4.5Zn Binary Alloy

Abstract

Hot mechanical working is among the remedies to improve the corrosion resistance of magnesium and its alloys as the third generation of biomaterials. In the present study, Mg-4.5Zn alloy was extruded at different temperatures (300°C, 350°C, and 400°C) and ratios (6:1, 12:1, and 18:1). Optical and scanning electron microscopes were used to characterize the microstructure evolutions of the alloy after the extrusion. The degradation behavior of the alloy after extrusion was studied in the simulated body fluid using immersion and electrochemical tests. Results showed that a decreasing extrusion ratio reduces the number of dynamically recrystallized grains as well as the extrusion shearing fringe parallel lines. Besides, the alloy extruded at higher temperature is relatively larger with few dynamic recrystallized grown grains. It was revealed that the corrosion resistance of the extruded alloy is linearly enhanced with decreasing grain size. Moreover, a higher extrusion ratio results in a lower corrosion rate, while a higher extrusion temperature leads to a higher corrosion rate. The results also showed that the alloy extruded at 300°C and 18:1 ratio possesses the finest grain size (18.2 μm) and the most equiaxed grains, which provide the lowest electrochemical corrosion rate (0.89 mm/year).