Study On The Surface Treatment Of The New Type Degradation Mg-Zn-Zr-Ca-Ag Alloy And Its Properties

To improve the mechanical properties and corrosion resistance of Mg-Zn-Zr-Ca-Ag alloy,the Mg-Zn-Zr-Ca-Ag alloy was studied systematically in this paper.Firstly,the microstructure and properties of Mg-Zn-Zr alloy,Mg-Zn-Ca alloy and Mg-Zn-Zr-Ca-Ag alloy were studied.Secondly,this paper investigated the heat treatment methods of the Mg-Zn-Zr-Ca-Ag alloy and determined the process of solution treatment and aging treatment,the effects of solid solution and aging heat treatment on microstructure and properties of Mg-Zn-Zr-Ca-Ag alloy were studied subsequently.In order to improve the corrosion resistance of the alloy,the FHA coating was prepared on the surface of the alloy,and the biological safety of the FHA coating was evaluated in detail.Finally,the effect of phytic acid/Ca-P treatment on the surface morphology and corrosion resistance of Mg-Zn-Zr-Ca-Ag alloy was studied in consideration of the cost of environmental protection and coating preparation.The results are as follows:(1)Compared to the Mg-3Zn-0.8Zr and Mg-3Zn-0.3Ca alloys,the number and species of the second phases were significantly increased and their distribution were fine and dispersed.After hot extrusion,the average grain size of Mg-Zn-Zr-Ca-Ag alloy is 2-3?m.After aging,the yield strength of the alloy increased to 355.527 MPa dramatically.The corrosion resistance of Mg-Zn-Zr-Ca-Ag alloy after aging treatment was worse than that of alloy with solid solution treatment,but better than that of untreated alloy.The results of cytotoxicity tests show that the Mg-Zn-Zr-Ca-Ag alloy has a certain degree of antibacterial activity to some extent;the cell proliferation rate was as high as 26.3%.(2)At HF concentration of 20%,the optimum treatment process is HF6h+Ca-P60 min.Under this treatment process,the composition of the coating is fluorine apatite,the FHA is needle-shaped crystal and has a certain orientation.The corrosion resistance of the alloy treated by FHA was better than that of the untreated alloy.After immersion,the corrosion rate of Mg-Zn-Zr-Ca-Ag coating on the surface of FHA alloy was 12%,and the average corrosion rate in SBF solution was 0.907mm/y.Cytotoxicity tests showed that the FHA coating is biological safety.(3)The best parameters of phytic acid/Ca-P is put samples in phytic acid solution at 45? for 60 minutes,then take samples in Ca-P solution at temperature 85 ? for 150 minutes.Under this treatment process,the morphology of coating surface is nano-scales,clusters and grow in a certain orientation and corrosion resistance of the treated Mg-Zn-Zr-Ca-Ag alloy was better than that of the untreated alloy.