The effects of alloying with Cu and Mn and thermal treatments on the mechanical instability of Zn-0.05Mg alloy.

The detrimental effect of natural aging on mechanical properties of zinc alloys restricts their application as bioresorbable medical implants. In this study, aging of Zn-0.05Mg alloy and the effect of 0.5 Cu and 0.1 Mn (in weight percent) addition on the microstructure and tensile properties were studied. The alloys were cold rolled, aged and annealed; aiming to investigate the effects of precipitates and grain size on the mechanical properties and their stability. TEM analysis revealed that in ultrafine-grained binary Zn-0.05Mg alloy, the natural aging occurred due to the formation of nano-sized Mg2Zn11 precipitates. After 90 days of natural aging, the yield strength and ultimate tensile strength of Zn-0.05Mg alloy increased from 197±4 MPa and 227±5 MPa to 233±8 MPa and 305±7 MPa, respectively, while the elongation was drastically reduced from 34±3% to 3±1%. This natural aging was retarded by adding the third element at either 0.1Mn or 0.5Cu quantities, which interacted with Mg in Zn solid solution and impeded the formation of Mg2Zn11 precipitates. The addition of Cu and Mn elements increased alloy's strength, ductility, and its mechanical stability at a room temperature. The measured tensile strength and elongation were 274±5 MPa and 41±1% for Zn-0.1Mn-0.05Mg and 312±2 MPa and 44±2% for Zn-0.5Cu-0.05Mg, respectively. Annealing the alloys at elevated temperatures caused increase in both grain size and dissolution of secondary phases, and both affected alloy deformation mechanisms.