Effect of 1.0 wt. % Zn addition on the microstructure, mechanical properties, and bio-corrosion behaviour of micro alloyed Mg-0.24Sn-0.04Mn alloy as biodegradable material

Magnesium and its alloys have been regarded as potential implant biomaterials due to their desirable biocompatibility, biodegradability and good mechanical properties. However the low strength and high degradation rate are the main drawbacks of pure magnesium. The current research investigates the mechanical and bio corrosion behavior of Mg-0.24Sn-0.04 Mn and Mg-0.24Sn-1.16Zn-0.04 Mn alloys containing small additions of cost effective biocompatible alloying elements (Sn, Zn and Mn) for biomedical implants. As the application of different processing techniques are rarely found in the literature, the effect of four different processing techniques on the alloys behavior is also investigated. The results are correlated with the microstructural parameters. The processing techniques include casting followed by heat treatment, hot extrusion and hot rolling. The cast / heat-treated tensile strength reached 162.2 MPa with 5.8 % elongation to rupture for the Mg-0.24Sn-0.04 Mn alloy (binary alloy) while for the alloy containg zinc addition (ternary alloy) a higher ultimate tensile strength of 243.8 MPa was obtained with an elongation of 2.9 %. By applying hot forming on the binary alloy, a large improvement in ultimate tensile strength and elongation was obtained, reaching 219.6 MPa and 7.9 % for extruded condition and 178.8 MPa and 9.1 % in hot rolled condition. In the ternary alloy the zinc addition raised the tensile strength to 269.2 MPa with a remarkable increase in elongation reaching 16.5 % for the extruded condition, while with hot rolling the strength was reduced to 223 MPa with an improvement in elongation to reach 5.2 %. These variation of properties are discussed in view of microstructure parameters using OM, SEM, EDX and XRD analysis. Regarding the corrosion rate in Hank's solution, it reached 0.82, 0.71 and 0.51 mm/y, for the binary alloy in cast/heat treated, extrusion and rolled condition, respectively. The addition of Zn had a negative effect on the corrosion rate as it increased to 1.88, 0.95, and 2.87 mm/y for cast/heat treated, extrusion and rolled conditions respectively. In general, the results indicate that by controlling the alloy composition and processing technique, Mg alloys containing small amounts of low cost alloying elements are promising for load bearing bio degradable orthopedic applications.