Fabrication And Properties Of Zn/Mg Laminate Composites For Orthopedic Application

Magnesium alloy has good biocompatibility to avoid immune rejection after implantation,and the comprehensive mechanical properties similar to human bone can avoid the"stress occlusion"effect,low cost,good processing and molding performance,and has great application potential as bone implant materials.But the rapid degradation rate of magnesium and its alloys in the body and the uncontrollable degradation are the bottleneck problems of the promotion and application of magnesium alloys in orthopedics and other medical fields.Zinc alloy has a relatively moderate corrosion degradation rate in body fluids,which has been a research hotspot in the field of degradable biomedical metal materials in recent years.Zinc alloy has good biocompatibility,zinc ions have bactericidal effect,and zinc is also a necessary trace element for the human body,but zinc strength is low（cast tensile strength is about 20 MPa）,brittle and easy to creep,density and elastic modulus are relatively high;The degradation rate is slightly slower;The threshold value initiated by zinc ions is an order of magnitude lower than that of magnesium.Therefore,neither magnesium alloys nor zinc alloys alone can independently meet the conceptual requirements of biological bone healing.In this paper,zinc-magnesium bimetallic layered composites were fabricated by composite co-extrusion at 543 K and 563 K temperatures,respectively,and the advantages of magnesium alloy and zinc alloy as degradable biomedical materials were complemented.The outer component of the composite is Zn-1Cu,and the core component is Mg-2Zn-0.1Ca.The interfacial microstructure,interfacial shear strength,compressive mechanical properties,in vitro corrosion degradation behavior and antibacterial properties of zinc-magnesium bimetallic layered composites were studied.The specific conclusions are as follows:（1）The interface of the prepared zinc-magnesium bimetallic layered composite has no defects such as cracks or voids,and the interface produces a good metallurgical bond.The average thickness of the interfacial diffusion layer of the composite extruded at 543 K temperature was 3.1μm,and the average thickness of the interfacial diffusion layer of the composite extruded at 563 K temperature was 3.8μm.From the scanning photos of the interface,it can be seen that the interface diffusion layer is divided into two layers,and after analysis,it can be seen that the diffusion layer is mainly composed of Mg Zn₂and Mg₂Zn₁₁,the part near the magnesium alloy is hard and brittle Mg Zn₂phase,and the part near the zinc alloy is the Mg₂Zn₁₁phase.After diffusion heat treatment,the thickness of the interfacial bonding layer increases.（2）The average hardness of the outer zinc alloy part of the zinc-magnesium bimetallic layered composite is 70.81 HV,and the average hardness of the core magnesium alloy part is 65.70 HV.The hardness of the Mg Zn₂phase of the interfacial diffusion layer is 275.70 HV-289.20 HV,and the hardness of the Mg₂Zn₁₁phase is278.26 HV-289.79 HV.After diffusion heat treatment,the average hardness of zinc alloy part and magnesium alloy part decreased to 68.68 HV and 57.79 HV,respectively.The compression yield strength of the composites extruded at 543 K and563 K reached the highest values before diffusion heat treatment,which were 208.38MPa and 184.58 MPa,respectively,and the yield strength values had little relationship with the thickness of the zinc alloy layer.The ultimate compressive strength of both was also the highest before diffusion heat treatment,493.61 MPa and473.10 MPa,respectively,and the ultimate compressive strength decreased with the increase of zinc alloy layer thickness.With the extension of diffusion heat treatment time,the yield strength and ultimate compressive strength of the composite decreased and the plasticity increased.（3）The interfacial shear strength of the composites extruded at 543 K and 563 K temperatures was the highest before diffusion heat treatment,which was 109.34 MPa and 128.55 MPa,respectively.With the extension of diffusion heat treatment time,the interfacial shear strength decreases.（4）The interfacial bonding strength of the composites extruded at 543 K and 563K was the highest before diffusion heat treatment,at 109.34 MPa and 128.55 MPa,respectively.With the extension of diffusion heat treatment time,the interfacial bonding strength decreases.（5）By comparing the antibacterial experimental results of composite materials,Zn-1Cu alloy and magnesium alloy with corrosion-resistant coating,it can be seen that the composite material and Zn-1Cu alloy have similar antibacterial properties and show good antibacterial properties against both bacteria,while the antibacterial effect of magnesium alloy with coating is not obvious.