Microstructure Control And Performance Study Of Rolled Zn-Mg Alloy

With the development of medical technology,traditional inert materials can no longer meet the development of implant materials.Fe-based and Mg-based degradable materials are challenging to use as suitable biodegradable materials due to the mismatch between the degradation rate and the patient’s healing time.Zn-based materials have great potential as biodegradable materials due to their suitable mechanical and degradation properties.However,pure zinc’s poor mechanical properties cannot meet implant materials’requirements.Therefore,in this paper,Zn-x Mg（x=0.6,0.8,1.0）alloys were prepared by adding different Mg contents,and the as-cast Zn-x Mg alloy was thermally rolled with different deformation amounts.Then,the alloy with excellent properties was subjected to 180 days of room temperature natural ageing to study the effects of Mg elements,rolling,and natural ageing on the microstructure and properties of the alloy.The results were as follows:After adding the Mg element,the alloy consisted of a matrix organization and a sheet-like distribution of eutectic organization.The grain size of the as-cast Zn-Mg alloy gradually decreased with increased Mg content.The gradual increase of eutectic structure impedes the movement of dislocations in plastic deformation.It increases the alloy’s tensile strength and yield strength by 2.3-2.8 times and 3.3-3.8 times,respectively,compared to pure Zn.At the same time,the Mg₂Zn₁₁phase in the eutectic organization also caused a 39%-60%decrease in the elongation of the alloy（compared to pure Zn）.The corrosion rate of the as-cast alloys accelerates with the increase of Mg elements,and the corrosion degree gradually deepens,and the more corrosion-sensitive nature of the Mg₂Zn₁₁ phase in the eutectic organization causes more severe corrosion at the grain boundaries of the alloyAfter rolling,the grain size of Zn-Mg alloy is uniform and decreases with the increase of deformation.The eutectic structure is broken and dispersed at the grain boundary,so the alloy’s tensile strength,yield strength and elongation are improved.The texture strength of the alloy increases with the increase of rolling deformation,and the texture type changes from a variety of composite textures to a single texture type.The rolling treatment causes Mg₂Zn₁₁ to break and disperse at grain boundaries.The larger the deformation,the higher the degree of dispersion,so the faster the alloy’s corrosion rate and corrosion rate will gradually slow down with time.In the natural ageing at room temperature,the precipitation of the minimal size Mg₂Zn₁₁ phase in the alloy leads to the change of mechanical properties.In contrast,the high grain boundary density of the rolled alloy leads to the precipitation of the Mg₂Zn₁₁ phase more easily than the cast alloy,and the change in mechanical properties is more significant.The alloy’s yield strength and tensile strength increase with the extension of the natural ageing time,and the elongation after fracture gradually decreases,and the magnitude of change of both strength and elongation after fracture gradually becomes slower with the ageing time.In addition,the electrochemical corrosion rate of the alloy has slightly increased with the extension of the natural ageing time,in which the rolled state of the alloy is more obvious than the cast alloy.In summary,adding alloying element Mg and rolling can significantly improve the properties of Zn-Mg alloys.Among them,the mechanical properties of the 70%rolled Zn-0.8Mg alloy meet the clinical implantation standards,and it has a suitable degradation rate,which is expected to become a new type of biodegradable implant material.