| Magnesium alloys can be used as new type of biological medical implant materials with the advantage of mechanical compatibility,biocompatibility and biodegradability,etc.Ca and Zn have strong effect on grain refinement and aging in Mg-Zn-Ca ternary alloy.Many researchers pay more and more attention to the Mg-Zn-Ca alloys because Ca and Zn are the constant elements of our human body.At present,the research of Mg-Zn-Ca alloys is mainly focused on controlling the content of Zn and Ca,adding alloying elements and surface treatment to improve corrosion resistance.However,the mechanical properties are rarely involved.Magnesium alloys need higher corrosion resistance and mechanical properties as biomedical implant materials.The research reports on improving both corrosion resistance and mechanical properties of magnesium alloys at the same time are few.Effects of high strain rate rolling on microstructure and properties of the Mg-4Zn-xCa alloys and the grain size and the second phase on corrosion behavior of Mg-4Zn alloy are systematically investigated in this paper.The main research results are given below:(1)Effects of high strain rate rolling on microstructure and mechanical properties of Mg-4Zn-xCa alloys are investigated.Compared with the as-cast alloy,the as-rolled alloys have dynamic recrystallization grains with the finer sizes.The lower content and the decreased size of the second phase and its homogenous distribution,contribute to the great improvement of the strength and elongation greatly.The tensile strength and the yield strength of Mg-4Zn-0.9Ca alloy are 300 MPa and 278 MPa respectively,about 82.9% and 275.7% higher than the as-cast alloy.With the increase of the Ca content,the strength and elongation of the as-cast alloy are decreased,and the strength of the as-rolled alloy is increased.(2)Effects of high strain rate rolling on the corrosion resistance and the residual tensile strength of the Mg-4Zn-xCa alloys are investigated.The corrosion resistance and the residual tensile strength of the as-rolled alloy are greatly improved,since the finer grain size,and the finer and the homogenously distributed second phase are involved.The Mg-4Zn alloy exhibits the best corrosion resistance and the highest residual tensile strength.Compared with the as-cast Mg-4Zn alloy,the mass loss of the as-rolled alloy soaked in 0.9%NaCl solution for 7 days is 41.6mg,about 80.4% lower.The residual tensile strength is the highest among all the alloys,high up to 217 MPa,about 186.8% higher.With the increase of the Ca content,the corrosion resistance of the as-cast alloys are increased before reduced,but the as-rolled state alloys are decreased.(3)Effects of alloy states as well as the grain size and the second phase on the corrosion resistance of the Mg-4Zn alloy are investigated.The corrosion behavior of the as-cast alloy is intergranular corrosion,and the average corrosion rate is gradually increased with the increasing soaking time.However,the corrosion behavior about the as-rolled state alloy is filiform corrosion,and the average corrosion rate is gradually decreased with the increasing soaking time.The corrosion resistance of the high strain-rate rolled Mg-4Zn alloy is superior to the conventional rolling for 3 passes of the Mg-4Zn alloy and the high strain-rate rolled ZK60 alloy,but is inferior to the high strain-rate rolled pure Mg and the high strain-rate rolled AZ91 alloy.As for the as-rolled Mg-4Zn alloys solution treated at 400 ?,the mass loss soaked in 0.9%NaCl solution for 7days decreases with the increasing grain size at first and then keeps a constant level.As for the as-rolled Mg-4Zn alloys aged at 160?,the mass loss decreases with a prolonged aging time during the underaged stage and is the lowest with the peale aging for 12 h,while it increases with a prolonged aging time during the overaged stage. |
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