Effect Of Ca And Sr Microalloying And Aging Treatment On Corrosion Behavior Of Deformed Mg-4Zn Alloy

Magnesium alloy has excellent mechanical compatibility,biocompatibility and biodegradability,which makes it enjoy the laudatory name of "revolutionary metal bio material".However,due to the poor corrosion resistance of magnesium alloy,stress corrosion cracking is easy to occur in human environment,which leads to premature failure of magnesium alloy.At present,there are few studies on stress corrosion cracking of magnesium alloys,so it is very necessary to explore the mechanism of stress corrosion cracking of magnesium alloys and improve their corrosion resistance and stress corrosion cracking properties in order to promote the application of magnesium alloys in the field of biomedical materials.In this paper,the effects of Ca?Sr microalloying and aging treatment on the micro structure,mechanical properties,corrosion resistance and stress corrosion cracking resistance of as-HRSSed Mg-4Zn alloy are systematically studied.On this basis,the effect of trace Sr on the biocompatibility of as-HRSSed Mg-4Zn alloy is further studied.The main conclusions are as follows:(1)The effects of trace Ca,Sr on the micro structure and mechanical properties of as-HRSSd Mg-4Zn alloy are studied.The results show that trace Ca and Sr can refine the grain size of as-cast and as-HRSSed Mg-4Zn alloy(the grain size less than 4 ?m),and improve the micro structure uniformity of the alloy.Trace Ca,Sr can improve the mechanical properties of as-HRSSed Mg-4Zn alloy to a certain extent,increasing the yield strength,tensile strength and elongation to rupture.The as-HRSSed Mg-4Zn-0.1Sr alloy has the best mechanical properties,with the yield strength of 201 MPa,the tensile strength of 285 MPa and the elongation of 31.9%.(2)The effects of trace Ca,Sr on the corrosion properties of as-HRSSed Mg-4Zn alloy are studied.The results show that with the increase of the Ca content(?0.3wt.%),the corrosion resistance of as-HRSSed Mg-4Zn-xCa alloy first improves and then deteriorates.The as-HRSSed Mg-4Zn-0.1Ca alloy has the best corrosion resistance.The corrosion rate in Hank's solution is 0.75 mm/y,the Ecorr is-1.55 V,and the icorr is 7.05 ?A/cm2.With the increase of the Sr content(?0.2wt.%),the corrosion resistance of as-HRSSed Mg-4Zn-ySr alloy becomes better.The as-HRSSed Mg-4Zn-0.2Sr alloy has the best corrosion resistance.The corrosion rate in Hank's solution is 0.68 mm/y,the Ecorr is-1.51 V,and the icorr is 6.14 ?A/cm2.(3)The effects of trace Ca,Sr on stress corrosion cracking of as-HRSSed Mg-4Zn alloy are studied.The results show that trace Ca,Sr can effectively improve the stress corrosion cracking resistance of as-HRSSed Mg-4Zn alloy and reduce the stress corrosion sensitivity index(Iscc).The as-HRSSed Mg-4Zn-0.2Sr alloy has the best stress corrosion cracking property,UTSin air=268 MPa,?in air=33.5%,UTSin Hank's=195 MPa,?in Hank's=7.2%,Iscc=0.41.(4)The effects of aging treatment on the corrosion resistance of Mg-4Zn-xCa alloy are studied.The results show that after high temperature aging at 160C/48h,the corrosion resistance of the as-solutioned Mg-4Zn-xCa alloy becomes worse at first,then better and then worse with the prolonged aging time,but the corrosion resistance of the as-aged alloy is worse than that of the solid as-solutioned alloy.After aging at different temperatures(70-120?)for 10 h,it is found that the corrosion resistance of the as-solutioned or the as-HRSS ed Mg-4Zn-xCa alloy increases at first and then decreases with the increasing temperature,and the rule of the as-solutioned alloy is consistent with that of the as-HRSSed alloy.(5)The effects of trace Sr on biocompatibility of as-HRSSed Mg-4Zn alloy are studied.The results show that in the early stage of cell culture,the as-HRSSed Mg-4Zn-0.1Sr alloy has a higher cell proliferation rate than pure Mg and the as-HRSSed Mg-4Zn alloy,and the cytotoxicity grade is 0 or 1.The Sr addition can promote cell growth at the early stage and is beneficial to cell adhesion and information transmission between cells.As-HRSS ed Mg-4Zn alloy and Mg-4Zn-0.1Sr alloy do not meet the requirement for the hemolysis rate,but the Sr addition can effectively reduce the hemolysis rate of the material.Platelets are spherical and quite a few are detected on the surface of the as-HRSSed Mg-4Zn-ySr alloy.The as-HRSSed Mg-4Zn-ySr alloy has good anticoagulant properties.