| In recent years,with the gradual expansion of the market for biomedical magnesium alloy and increased demand for industrial products,it is of great academic significance and application value to develope a novel biomedical magnesium-based alloy with excellent mechanical properties,corrosion resistance and biocompatibility.In the present work,we have designed a novel Mg-3Sn-1Zn alloy,and comprehensively investigated the microstructure and performance of Mg-3Sn-1Zn Alloy undergoning different extrusion deformation processes In order to further improve the performance of Mg-3Sn-1Zn alloy,a Mg-3Sn-1Zn-0.5Mn alloy has been newly developed.A comprehensive investigation of the microstructures,performance and deformation mechanisms of Mg-3Sn-1Zn-0.5Mn alloys with different deformation was conducted.The experimental results indicate an inhomogeneous microstructure of ?-Mg dendrites grains for as-cast Mg-3Sn-1Zn alloy and Mg-3Sn-1Zn-0.5Mn alloy with second phase particles along the grain boundaries and in the grains.The as-solution alloy has microstructures of large equiaxed grains with the second phase fully integrated into the matrix,so as to has improved comprehensive performance.Under the extrusion temperature of 290? and with extrusion ratios of 8,16 and 25,the comprehensive properties of the Mg-3Sn-1Zn alloy are the best.The microstructure of alloy is a fine equiaxed and shear zone in the same time.The comprehensive properties in the as-extruded alloys decreased with the increase of extrusion ratio.The extrusion temperature of 310?-370? have the similar performance.When the extrusion temperature of 290? of Mg-3Sn-1Zn-0.5Mn alloy with extrusion ratios of 8.16 and 25,the comprehensive properties of the composites are the best,the microstructure of alloy is a fine equiaxed and shear zone in the same time,the extrusion temperature of 310?-370? have the similar performance.Mg-3Sn-1Zn-0.5Mn alloy has better comprehensive properties than Mg-3Sn-1Zn alloy:under the same extrusion ratio,if the tensile strength increases about 10-20MPa,the elongation increases about 2-6%accordingly.And the corrosion potential raises from-1.6V for the Mg-3Sn-1Zn alloy to-1.5V for the Mg-3Sn-1Zn-0.5Mn alloy,whereas the corrosion current is reduced by approximately 60%.Hemolysis of Mg-3Sn-1Zn alloy is generally higher than 5%while hemolysis of Mg-3Sn-1Zn-0.5Mn alloy is 5%or lower.The microstructure evolution of Mg-3Sn-1 Zn-0.5Mn alloy has the following characteristics:1)the grain size of Mg-3Sn-1Zn-0.5Mn alloy shows decreasing trend with increasing deformation.2)The Mn particles are present along the a-Mg grain boundaries of Mg-3Sn-1Zn-0.5Mn alloy solid solution,and the plate like or rod like Mg2Sn precipitates distribute evenly in the alloy matrix after extrusion deformation.3)Quantity of twins in Mg-3Sn-1Zn-0.5Mn alloy decreases with the increased deformation.Under small amount of extrusion deformation,morphology of the twins in the solid solution of Mg-3Sn-1Zn-0.5Mn alloy will transform.Twins after transformation may then go through the process of detwinning,when new twins will generate simultaneously due to extrusion.Since the amount of twins experiencing detwinning is comparable to that of the newly-generated twins,the final amount of twins changes slightly.Under large amount of extrusion deformation,the amount of twins undergoing detwinning in the Mg-3Sn-1Zn-0.5Mn alloy increases,moreover,the fine grains and large amount of Mg2Sn second-phase precipitates inhibit the generation of new twins,both of which lead to the sharp decrease of the final amount of twins.The deformation mechanism of Mg-3Sn-1Zn-0.5Mn alloy mainly consists of slipping and twinning.Dislocations movement and multiplication in deformation process will cause mutual tangling and pinning of dislocations,and be blocked by the grain boundaries,which finally lead to a stop of the dislocation movement.Twinning could easily occur in the grains without adequate slipping to facilitate plastic deformation.Deformation twins and detwinning occur simultaneously during extruding.Under large amount of extrusion deformation(extrusion ratio 64),the size of grain after dynamic recrystallization is small and accordingly the grain boundary slip plays a crucial role.In solid solution state and under extrusion deformation,the orientations of twins in Mg-3Sn-1Zn-0.5Mn alloy are all {1012}<1011>.In solid solution state,the growth mechanism of {1012} twins in Mg-3Sn-1Zn-0.5Mn alloy is typical twin-dislocation mechanism,and the {1012} twin boundary deviates in small angle from the {1012} twinning plane.Under extrusion deformation,{1012} twin boundary in Mg-3Sn-1Zn-0.5Mn alloy is not in the {1012} twinning plane and moreover the orientation of {1012}twin deviate severely from the theoretical angle of 86.3°.The growth mechanism of{1012} twins of as-extruded Mg-3Sn-1Zn-0.5Mn alloy is Shuffling and shearing mechanism. |
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