Preparation And Surface Modification Research Of Porous Mg-Ag Matrix Alloy

Porous Mg-Ag and Mg-Ag-Zn alloys were fabricated by powder metallurgy method choosing Mg,Ag,Zn powder and NH₄HCO₃ as raw materials.The effects of the NH₄HCO₃contents,pressing pressure,sintering temperature,the content of Ag element on porosity,compressive strength,microhardness are investgated.The microstructure of pore wall of porous Mg-Ag and Mg-Ag-Zn alloys with different Ag content was observed and the phase constitution was analyzed.The corrosion resistance of two kinds of Mg alloys was measured.In the Na₂SiO₃ electrolyte,the porous Mg-Ag and Mg-Ag-Zn alloys were modified by plasma electrolytic oxidation.The influences of current,time,contents of Ag element on oxidation voltages,film morphology and film thickness of porous Mg-Ag matrix alloys were studied.The phase constitution and corrosion resistance of the oxidated films on the porous Mg-Ag and Mg-Zn-Ag alloys samples was analyzed and tested.The results show that the porosities of sintered products increase by increase NH₄HCO₃content.With the increase of pressing pressure or sintering temperature,the porosities of sintered products reduce,but the compressive strengths improve.With the increase of Ag content,the porosities of sintered productes become lower,but the compressive strength and microhardness first improve and then reduce.The porous Mg-3Ag alloys with NH₄HCO₃ of14%,pressing pressure of 60 MPa are sintered at 600?,the porosity,compressive strength and microhardness are 19.4%,34.7 MPa and 47.6 HV.The porous Mg-2Ag-1Zn alloy by NH₄HCO₃ of 14%,pressing pressure of 60 MPa are sintered at 600?,the porosity,compressive strength and microhardness are 19.1%,34.2 MPa and 46.9 HV.SEM analysis show when Ag element or Ag and Zn mixed elements are added in the Mg matrix,the pore cells have finer crystallite dimension and high sintering density.Porous Mg-3Ag and Mg-2Ag-1Zn have similiar compact degree in pore cell.XRD and EDS analysis show the composition of porous Mg-3Ag and Mg-2Ag-1Zn alloy is?-Mg phase.Porous Mg-4Ag and Mg-3Ag-1Zn alloys are composed of?-Mg and Mg₄Ag phases.The corrosion resistance show the porous Mg-Ag alloys have better corrosion resistance than the porous Mg.The corrosion rate of porous Mg-3Ag is lowest and the corrosion surface has little corrosion products.However,the surface of porous Mg alloy has a lot of corrosion product.Porous Mg-2Ag-1Zn has similiar corrosion rate and corrosion surface,which shows two kinds of alloys have similiar and better corrosion resistance.With the increase of Ag content in 0⁴ wt%domain,the V₁,V₂,V₃ and the oxidated layer thickness first improve and then reduce.After oxidated with 3 A for 2 min,the oxidation coating quality of porous Mg-3Ag and Mg-2Ag-1Zn alloys is optimal.The layer thickness with homogeneous pores is 41.5?m and 42.3?m.XRD and EDS analysis show that the oxidated layer are composed of MgO and Mg₂SiO₄ phases.Corrosion resistance measurement show the samples without micro-arc oxidation always have obvious weight loss.But wights of porous Mg-3Ag and Mg-2Ag-1Zn alloy after micro-arc oxidation first increase and then decrease,which show that the corrosion resistance of porous Mg-3Ag and Mg-2Ag-1Zn alloy are improved.