Effects of minor Sr addition on microstructure, mechanical and bio-corrosion properties of the Mg-5Zn based alloy system

Effects of minor Sr addition (0, 0.2, 0.6 and 1.0 mass%) on microstructure, mechanical and corrosion properties of the as-cast Mg-5Zn-based alloy system are investigated by SEM, XRD, mechanical testing and etc. The Sr-free alloy is composed of three phases i.e. α-Mg, Mg7Zn3 and MgZn, while the alloys with the Sr addition of 0.6% or higher consist of α-Mg, Mg7Zn3, MgZn and Mg11Zn4Sr3. Minor Sr addition can effectively refine grains of the as-cast Mg-5Zn alloy and bring about more grain-boundary compounds. The as-cast alloy with 0.2%Sr addition exhibits the best combined mechanical properties with the ultimate tensile strength and elongation of 233 MPa and 15%. Corrosion tests in 0.9%NaCl solution and Hank's solution show that the degradation rate decreases significantly in the following order of Mg-5Zn, Mg-5Zn-0.6Sr, Mg-5Zn-1Sr and Mg-5Zn-0.2Sr. The as-cast Mg-5Zn-0.2Sr alloy also shows the optimal corrosion resistance both in 0.9%NaCl solution and in Hank's solution.