Microstructures, mechanical properties and in vitro corrosion behavior of biodegradable Zn alloys microalloyed with Al, Mn, Cu, Ag and Li elements

In this work, Zn microalloyed with Al, Mn, Cu, Ag and Li was cast, annealed and extruded. The results showed that addition of multiple trace elements causes significant change in the microstructures, mechanical properties and corrosion behavior of Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag (1ZM), Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag- 0.1Li (2ZM-0.1Li) and Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag-0.35Li (3ZM-0.35Li) alloys. Two ternary phases with the approximate compositions of Al13Mn3Zn34 and Al10MnZn89 phases are formed in the casting and annealing processes of these alloys, respectively. Wavy β-LiZn4 lamellae that have not been extensively reported are precipitated from the primary Zn dendrites in the casting process of ZM-0.35Li alloy. Also, Zn laths are precipitated from the eutectic β-LiZn4 phase in the annealing process of ZM-0.35Li alloy. The above-mentioned phases are crushed or elongated in the as-extruded alloys, which play an important role in improving the strength of the alloys. All the as-extruded alloys have typical (0001) basal texture, accompanied with relatively low {0001}<112¯0> slip and high {101¯2}<101¯1¯> twinning Schmid factors, which are advantageous and disadvantageous to the strength enhancement of the alloys, respectively. All the as-cast alloys exhibit poor mechanical properties, especially low ductility. The as-extruded ZM alloy exhibits ultrahigh ductility, with an elongation of up to 82.2% ± 2.94%. The as-extruded ZM-0.35Li alloy shows the best comprehensive mechanical properties, with yield strength, ultimate tensile strength, elongation and hardness of 380 ± 1.6 MPa, 449 ± 7.4 MPa, 62.3% ± 4.63% and 98 ± 1.4 HV, respectively. Electrochemical corrosion rates of the ZM, ZM-0.1Li and ZM-0.35Li alloys are 0.241 ± 0.004, 0.206 ± 0.006 and 0.189 ± 0.008 mm/year, respectively. In vitro immersion corrosion rates (after 26 d in SBF solution) of them are 0.134 ± 0.005, 0.125 ± 0.004 and 0.121 ± 0.003 mm/year, respectively. The as-extruded ZM-0.35Li alloy exhibits the best corrosion resistance.