| Magnesium and its alloy materials have great potential for application as biological implant materials due to their mechanical properties similar to human bones,good biocompatibility,and the ability to achieve complete biodegradation in vivo.However,the poor wear resistance and corrosion resistance of magnesium and its alloys in the physiological environment and relatively general biological activity have seriously hindered its further expansion in the medical system.Therefore,how to improve the mechanical properties,corrosion resistance and biological activity of bio-magnesium and its alloy implant materials becomes a key point for its further development and application.Mechanical shot peening process and cold spraying process are widely used to improve the properties of magnesium and its alloys due to their excellent technological characteristics.In addition,Zn is more electronegative than Mg,and it is also one of the essential elements for human body.Hydroxyapatite(HA)is a biologic ceramic material with good biocompatibility and bioactivity(osteo-conductivity).In this paper,the cast AZ91D magnesium alloy was strengthened by the best shot peening process(to obtain SPAZ91D),and then the pure Zn coating was cold-sprayed(to obtain SPAZ91D-Zn).Then the best shot peening process(to obtain SPAZ91d-SPZn)was further used.Finally,the surface of the cast AZ91D magnesium alloy was cold-sprayed with a composite coating of HA/Zn.The mechanical shot peening process under different parameters was used to strengthen the cast AZ91D magnesium alloy,to explore the effects of different shot peening pressure,different shot peening time and different bombardment distance on the properties of the hardened samples.Parameters can be found:bombarding distance relative blasting gas pressure and shot peening processing time to process more small,the influence of mechanical AZ91D magnesium alloy specimens after the shot blast machine for the sharp rise in mechanical properties,increased to about 2.0 times the surface microhardness,friction and wear performance rises to about 1.5 times,but its corrosion resistance performance deteriorated.The parameters optimized for mec-hanical shot peening process of the as-cast AZ91D magnesium alloy were as follows:gas pressure 0.2MPa,shot peening time 10min,shot peening distance 80mm,the best shot peening samples are referred to as SPAZ91D samples.The cold spraying velocity measurement test of Zn powder was conducted.The best cold spraying process was selected to spray pure Zn coating on the SPAZ91D sample,and the corrosion resistance was significantly increased.The mechanical shot peening process under different parameters was used to strengthen the SPAZ91D-Zn samples,and to explore the influence of different shot peening pressure and different shot peening time on the Zn coating.It can be found that:mechanical and mechanical properties of Zn coating increased after mechanical shot peening treatment,and the surface microhardness increased to about 1.5 times,and its corrosion resistance further increased,and the self-corrosion current decreased to 1/3 of the original AZ91D magnesium alloy.After optimizing the mechanical shot peening process of Zn coating,the parameters were:gas pressure of shot peening 0.15MPa,treatment time of shot peening 10min,blasting distance of shot peening 80mm,the best samples after shot peening are referred to as SPAZ91D-SPZn samples.In addition,four samples were immersed in hydrogen evolution experiments to compare their corrosion resistance in simulated body fluids.The overall corrosion rate was SPAZ91D>AZ91D>SPAZ91D-Zn>SPAZ91D-SPZn in order of size.Three kinds of composite powders 100wt.%HA/Zn(abbreviated as HA),70wt.%HA/Zn(abbreviated as H7Z3)and 30wt.%HA/Zn(abbreviated as H3Z7)were tested by cold spraying.The best cold spraying process was selected to spray the HA/Zn composite coating on the SPAZ91D-SPZn samples.It can be found that the corrosion resistance of Zn-H3Z7 double coatings has slightly increased,while that of Zn-HA and Zn-H7Z3 double coatings has slightly decreased.In addition,HA and HA/Zn composite coatings have good apatite generation ability during simulated body fluid immersion,showing good biological activity and compatibility. |
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