Materials Science & Engineering A 831 (2022) 142192 Available online 15 October 2021 0921-5093/© 2021 Elsevier B.V. All rights reserved. Mechanical and corrosion properties of extruded Mg–Zr–Sr alloys for biodegradable implant applications Faisal Kiani a , Jixing Lin b , Alireza Vahid c , Khurram Munir a , Cuie Wen a , Yuncang Li a, * a School of Engineering, RMIT University, Melbourne, Victoria, 3001, Australia b School and Hospital of Stomatology, Wenzhou Medical University, Wenzhou, 325027, China c Institute for Frontier Materials, Deakin University, Geelong, Victoria, 3217, Australia A R T I C L E INFO Keywords: Biodegradable Mg alloy Corrosion properties Extrusion Mechanical properties Mg–Zr–Sr alloys ABSTRACT Magnesium (Mg) alloys have been extensively studied for their potential application as biodegradable implants. Zirconium (Zr) and strontium (Sr) are some of the few elements that are considered both biocompatible and biofunctional. In this study, extrusion was performed on Mg–Zr–Sr alloys in order to further improve their mechanical and corrosion properties and to clarify the effects of Zr and Sr additions on the materials properties of Mg alloys. Results indicated that in the extruded Mg–Zr–Sr alloys, the intermetallic Mg 17 Sr 2 phases were accumulated at the grain boundaries, which triggered particle-stimulated nucleation, leading to reduced grain size and deformation twining. Increasing Zr content from 0.5 wt% to 3 wt% in the extruded Mg–xZr–1Sr (x = 0.5–3 wt%) alloys resulted in an increase of 25.4% in elongation and 5.9% in ultimate tensile strength. On the other hand, increasing Sr content from 1 wt% to 3 wt% in Mg–0.5Zr–xSr (x = 1–3 wt%) alloys improved only the tensile strength by 19.3% and the highest ultimate strength of 302 MPa was observed in extruded Mg–0.5Zr–3Sr. The tensile yield strength of extruded Mg–xZr–ySr (x = 0.035–3 wt%; y = 0.2–3 wt%) alloys ranged from 210 to 275 MPa. Compressive strength and strain of extruded Mg–Zr–Sr alloys ranged from 289 to 368 MPa and from 11.0% to 18.9%, respectively. The corrosion rates of the extruded Mg–Zr–Sr alloys ranged from 4.6 to 10.7 mm y 1 from potentiodynamic polarization tests. Overall, the extruded Mg–0.5Zr–3Sr showed optimum mechanical and corrosion properties and can be considered a promising biodegradable implant material. 1. Introduction Pure magnesium (Mg) has been known for its biomedical properties and its potential as a biodegradable implant material since the late 19th century. The major shortcomings experienced during those early studies were its inferior mechanical properties and high corrosion rate (CR) in vivo [1]. Consequently, alloying of Mg with suitable elements was adopted as one of the best ways to address these core problems. The selection of alloying elements in biodegradable Mg alloys is limited, as only a few elements fulfll the combined requirements of acceptable toxicity with enhancement of corrosion resistance [2]. A comprehensive evaluation of these alloying elements in Mg on the basis of mechanical and corrosion properties, as well as biocompatibility, was undertaken by Ding et al. [3], who suggested strontium (Sr), calcium (Ca), and zirco- nium (Zr) as the most suitable alloying elements for Mg, whereas zinc (Zn), manganese (Mn), yttrium (Y), and gadolinium (Gd) among some other rare earth (RE) elements were recommended for further research due to the availability of only limited data. Sr is considered an osteoconductive element [3]. Mg–Sr alloys showed improved bone mineralization, formation of Sr-substituted hy- droxyapatite (HA) and enhanced bone growth around the implant after implantation in mice femur [4] and in dog femoral artery [5]. Direct formation of new bone adjacent to the Mg–1Zr–2Sr implant was observed after 3 months implantation in rabbits [6]. In addition, radi- ography of the bone showed high mineral density and content; and Sr addition was confrmed to improve the osteointegrative properties in Mg–Zr–Sr alloys [6]. Furthermore, Sr promotes osteoblast maturation and was reported to improve the vertebral bone density and bone vol- ume at low dose [7]. A cell viability test of extruded Mg–0.5Sr showed normal and healthy MG63 cell morphology when cultured in Dulbecco’s modifed Eagle’s medium (DMEM) [8]. Moreover, better corrosion resistance was reported due to the formation of a Sr-substituted HA layer in simulated body fuid (SBF) and improved cell growth and prolifera- tion during in vivo experiments of Mg–0.5Sr [5]. * Corresponding author. E-mail address: yuncang.li@rmit.edu.au (Y. Li). Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea https://doi.org/10.1016/j.msea.2021.142192 Received 4 June 2021; Received in revised form 18 September 2021; Accepted 13 October 2021