Event Abstract Back to Event Effect of extrusion and annealing on the mechanical and corrosion properties of the magnesium alloys Zhigang Xu1, Sergey Yarmolenko1 and Jag Sankar1 1 North Carolina A&T State University, NSF ERC for Revolutionizing Metallic Biomaterials, United States Introduction: Mg-based alloys have shown remarkable advantages serving as biodegradable implant materials due to their excellent biocompatibility, closer elastic modulus to natural bone, and inherent biodegradation capability [1],[2]. However, the fast corrosion of Mg in the physiological system with high chloride concentration prevents its success in many biomedical applications. Recently, Mg-rare earth (RE)-based alloys gained a great deal of attention because these materials normally exhibit high strength and ductility, and the best corrosion performance [3]. In this project, the focus was placed on the study the effects of extrusion and post heat treatment on the texture development, mechanical and corrosion properties of Mg-RE-based alloys. Materials and Methods: Mg-1.0Zn-0.3Ca-1.5REs alloy was melted and cast under the protection of argon gas in a glove box. Solution treatment (T4) was performed at 500°C for 12 hours. Samples after T4 treatment were extruded at 400 °C with an extrusion ratio of 10. Heat treatments, i.e. annealing of the extruded alloy were carried out at temperatures of 250 ºC, 300 ºC, 350 ºC, 400 ºC, 450 ºC and 500 ºC, respectively, with a holding time of an hour. The microstructures of the as-extruded and annealed materials were observed with SEM. Their textures were determined with X-ray pole figures. The mechanical and corrosion properties were assessed with microhardness and electrochemical impedance spectroscopy (EIS). Results and Discussion: Fig. 1. Shows the microstructure of the as-extruded and the annealed alloys. In the as-extruded condition, the alloy has a grain size of ~5 µm. As shown in Fig.1 and 2, low temperature annealing at 250 ºC and 300 ºC only causes marginal grain growth and second phase dissolving. With the increased annealing temperature, both the grain growth and second phase dissolving become significant. EIS studies shows a general trend that with the increasing of the annealing temperature, the corrosion resistance was increased (as shown in Fig. 3.). Using X-ray pole figure method, MAX values which represent the texture intensity of each material were obtained and are shown in Fig. 4. As-extruded alloy had strong texture with MAX value 20.3. Annealing of for an hour at temperature 150°C below the extrusion temperature led to reduction of texture intensity about two (2) times due to recrystallization. Annealing for an hour at extrusion temperature left only one fourth of texture intensity. At temperatures higher than extrusion process, the texture almost disappeared and cannot be evaluated by pole figure due to insufficient statistics in the material with overgrown grains. Fig. 5 shows the microhardness in the cross-section plane of the as-extruded and annealed samples. Small grain size, the precipitation of the second phase particles plus high defect density produced the highest hardness in as-extruded state. Annealing at different temperatures led to different degrees of grain growth, second phase dissolving and defect alleviation. These changes may explain the non-linear reduction of the microhardness. Conclusion: The experiments revealed that extrusion leads to highly textured and small grain-sized microstructure of the Mg-Zn-RE based alloy. Annealing dissolves the second phase into the Mg-matrix, leading to grain growth to different extents depending to the annealing temperature. In general, the corrosion resistance of the materials is enhanced by annealing, while the microhardness weakened by the same process. The research was financially supported by the USA NSF sponsored Engineering Reseach Center of Revolutionizing Metallic Biomaterials.
Search from 250 M+ research papersSearch from 250 M+ research papers
Apr 3, 2024
Haitao Ling + 3
Open Access