Study On Ca And Ce/La Synergetic Strengthening Mechanism In Mg Alloy And Properties Of Its Protective Coating

Alloying is an effective way to improve mechanical properties of Mg alloys,since the mechanical properties of Mg alloys are sensitive to the grain size,texture and distribution of precipitates.The addition of proper alloying elements in Mg alloys could reduce the grain size,and modify the structure and morphology of secondary phase,orientation of precipitates,and then improve the mechanical properties.In the present study,we invesgated the effect of Ca-Ce/La synergistic addition on the microstructure,texture and tensile properties of Mg-Zn alloy.The results shows,compared with the sole Ca or Ce/La element,the Ca-Ce/La synergistic microalloying represents a more excellent strengthening effect in extruded Mg-Zn alloy,which is mainly attributed to the grain refinement during the extrusion process.Ca-Ce/La synergistic addition leads to the formation of many spherical secondary phase particles,which restricts the grain growth during the extrusion process,thus the tensile stress is improved.Besides,Ca-Ce/La addition results in the refinement of the secondary phases and precipitates,promoting the pinning effect for dynamic recrystallized grain growth and dispersion strengthening effect,which also contributes to the increased yield stress.Furthermore,Ca-Ce/La combined addition leads to the more uniform distributions of fine secondary phases,which can improve the ductility and promote the particle stimulated nucleation effect,resulting in a weak basal texture in extruded Mg-Zn alloy.The poor corrosion and wear resistances hinder the industrial applications of magnesium and its alloys.In this paper,a new graphene oxide(GO)coating,having great adhesion with Mg substrate,is fabricated on the surface of extruded Mg-Zn-Ca alloy,via the silane coupling agent.GO coating has fully covered the Mg substrate by an APTES intermediate layer via amidation reaction,and finally formed an overlapped structure with outstanding bonding strength by interlocked effects.The APTES and GOs,GOs and Mg substrate are bonded via Mg-O-Si and-C?O-NH-,respectively,representing strong adhesion stress,which make the coating difficult to peel off.APTES/GO coating,due to its stable chemical bond,can efficiently block the penetration of chloride ion to the surface of Mg substrate.Electrochemical measurements indicate that the anti-corrosion performance can be remarkably improved by silane/GO coating,because the stable covalent bonds within the coating effectively restrict the penetration of electrolyte into the Mg surface,representing an excellent corrosion barrier effect.The GO coating dramatically promotes the wear resistance,due to the superior bonding between the Mg substrate and GO sheets with high hardness and good lubricant effect.