Research On Microstructures And Properties Of Mg-Zn-Zr/Sr Alloy

Magnesium alloys have obvious advantages in biocompatibility and degradability,but its mechanical properties and corrosion performance have some shortcomings that cannot be ignored,which limits its application as a biomedical material.In this study,Mg-4Zn alloy improved the alloy properties with adding Zr and Sr elements.The microstructures and properties of Mg-4Zn-0.3Zr and Mg-4Zn-0.5Sr alloys with optimized composition were improved by heat treatment and hot extrusion,Mg-4Zn-0.3Zr and Mg-4Zn-0.5Sr alloys in the as-cast and hot-extruded state were subjected to corrosion resistance,corrosion tests such as weight loss test,pH test and electrochemical test.The results showed that adding 0.1wt.%,0.3wt.%,and 0.5wt.%Zr elements to Mg-4Zn alloy,respectively,when the Zr content was 0.3wt.%,the grain of Mg-4Zn-0.3Zr alloy was refined,the mechanical properties were increased,the tensile strength,yield strength and elongation were 188MPa,95MPa and 15.00%,respectively.After the solution treatment of the as-cast Mg-4Zn-0.3Zr alloy,the second phase gradually entered the matrix.As the increased of solution time,the strength and elongation of the alloy increased and then decreased,and reached the maximum value at 18h in solution treatment.The tensile strength,yield strength,and elongation of the alloy reached 203MPa,182MPa,and 17.17%,respectively.When aging for 1h,the tensile strength and yield strength of the alloy reached the maximum,which were213MPa and 188MPa,respectively.After hot extrusion,the alloy grains were refined.The tensile strength of the extruded Mg-4Zn-0.3Zr sample was 231MPa,the yield strength was205MPa,and the elongation was 18.63%.Compared with the as-cast condition,it increased by22.87%,115.79%and 24.20%,respectively.Adding 0.2wt.%,0.5wt.%,and 1.0wt.%Sr elements to Mg-4Zn alloy,when the Sr content was 0.5wt.%,the tensile strength,yield strength and elongation of Mg-4Zn-0.5Sr alloy were 161MPa,88MPa and 10.30%,respectively.After solution treatment for 18h,the second phase around the grain boundaries was solution into the matrix,and the tensile strength,yield strength,and elongation were 192MPa,99MPa and 12.06%,respectively.After aging for 8h,the MgZn phase was precipitated in large amounts on the grain boundaries and dispersed.The tensile strength,yield strength,and elongation of the alloy reached 223MPa,118MPa,and19.60%,respectively.After hot extrusion,The tensile strength of the extruded Mg-4Zn-0.5Sr was 252MPa,the yield strength was 227MPa,and the elongation was 19.86%.Adding Sr and Zr elements to Mg-4Zn alloy,respectively,the comparison analysis showed that the mechanical properties of as-cast Mg-4Zn-0.3Zr alloy were better than as-cast Mg-4Zn-0.5Sr alloy.After hot extrusion,The mechanical properties of the extruded Mg-4Zn-0.5Sr alloy were better than the extruded Mg-4Zn-0.3Zr alloy.It was due to the brittle and hard Mg₁₇Sr₂ phase precipitated along the grain boundaries in the alloy significantly affected the alloy properties.The second phase was broken and dispersed,which played a role of dispersion strengthen and improved alloy properties.The as-cast Mg-4Zn-0.3Zr,as-cast Mg-4Zn-0.5Sr,extruded Mg-4Zn-0.3Zr and extruded Mg-4Zn-0.5Sr alloys were tested for corrosion resistance.The test showed that the extruded Mg-4Zn-0.3Zr alloy had good corrosion resistance,the average corrosion rate of the extruded Mg-4Zn-0.3Zr alloy was the lowest.As the soaking time increased,the pH of the soaking solution gradually increased and then stabilized.The extruded Mg-4Zn-0.3Zr was the lowest of pH.The electrochemical test showed that the radius of high-frequency capacitance arc resistance of the extruded Mg-4Zn-0.3Zr alloy was the largest,corrosion current density was small,and self-corrosion potential was high.