Effects of Trace Sr on Microstructure, Mechanical Properties and Corrosion Resistance of Mg-0.2Zn-0.1Mn-xSr Biomaterials

The effects of adding trace Sr element on microstructure, mechanical properties and corrosion properties of Mg-0.2Zn-0.1Mn-xSr (x=0, 0.1, 0.2, 0.3, wt%) alloys were investigated. The results of microstructure observation reveal that the grain size of the alloy decreases with the increase of Sr content. The granular Mg17Sr2 phase is uniformly dispersed in the magnesium matrix, while the second phase grows up as the Sr increases. The results of mechanical properties investigated by tensile test at room temperature indicate that micro Sr can improve the yield strength and tensile strength. But the elongation decreases with the increase of Sr content. Degradation was studied using immersion tests in Kokubo solution. The corrosion rate is faster and the pitting is more likely to occur when the Sr content increases. The average corrosion rates of Mg-0.2Zn-0.1Mn-xSr (x=0, 0.1, 0.2, 0.3, wt%) measured by mass loss are 6.85 -> 6.01 -> 6.80 -> 7.52 mm/a. Trace Sr can improve the corrosion resistance of magnesium alloys. However, with the increase of Sr content, the magnesium alloys are more prone to pitting and intergranular corrosion, which in turn reduces the corrosion resistance of magnesium alloys. The bio-corrosion behaviors can be attributed to the grain refinement and the diffused second phase, which can promote the formation of corrosion product film. However, the bigger second phase in the matrix will accelerate the local corrosion, and reduce the corrosion resistance of magnesium alloy. The results show that Mg-0.2Zn-0.1Mn-0.1Sr has the best mechanical properties and corrosion resistance.