The Preparation Of Gradient Porous Mg-Zn Alloy And Its Surface Modification Research

Gradient porous Mg-Zn alloys were prepared by powder metallurgy method using Mg powder, Zn powder and NH4HCO3 as initial materials. The effects of the distribution of NH4HCO3, particle size of Mg powder, pressing pressure, sintering temperature, the content of Zn element on porosity, sintering shrinkage, compressive strength, microhardness are investgated. The compressive behavior of gradient porous Mg-Zn alloys was simulated by ANSYS software. The microstructure of pore wall of gradient porous Mg-Zn alloys with different Zn content was observed and the phase composition was analyzed. The corrosion resistance of gradient porous Mg-Zn alloys adding Zn element was measured. The gradient porous Mg-Zn alloys were micro-arc oxidated in the Na2SiO3 electrolyte. The effects of distribution of NH4HCO3, oxidation current density, oxidation time, content of Zn element on voltages, morphology and thickness of the oxidation coating were studied. The phase composition of the oxidation coating was analyzed and corrosion resistance of the gradient porous Mg-Zn alloys samples was measured.The results show that with the increase of NH4HCO3 in the inner layer, the porosities of sintered products increase and their sintering shrinkages decrease. With the increase of the particle size of Mg powder, pressing pressure, sintering temperature, and the content of Zn element, the porosities of sintered products decrease, but the sintering shrinkages increase. With the increase of Zn content, the compressive strength of sintered products first increase and then decrease. The gradient porous Mg-Zn alloys with 3wt% Zn, NH4HCO3 distribution of 20wt%-10wt%-20wt%, pressing pressure of 80 MPa are sintered at 600℃, the lateral compressive strength and Young’s modulous of sintered products are 30.8MPa and 1.14 GPa, the longitudinal compressive strength and Young’s modulous of sintered products are 41.2MPa and 1.71 GPa. The deformation characteristic and shear stress field of gradient porous Mg-Zn alloys at lateral and longitudinal compression are simulated and analyzed by ANSYS software. SEM analysis show when Zn element is added in the Mg matrix, the pore cells have fine grain size and high sintered density. XRD and EDS analysis show the gradient porous Mg-Zn alloy of 3wt% Zn is composed of α-Mg phase. When the content of Zn is 4wt%, the alloys are composed of α-Mg and MgZn2 phases. The corrosion resistance show the gradient porous Mg-Zn alloys have better corrosion resistance than the Mg matrix. With the increase of NH4HCO3 in the inner layer, the V1, V2, V3 all increase. With the increase of oxidation current density, the V1, V2, V3 and thickness of the oxidation coating all increase. With the increase of oxidation time, the V1, V2, V3 and thickness of the oxidation coating all increase. With the increase of Zn content, the V1, V2, V3 first decrease and then increase a little, but the thickness of the oxidation coating first decrease and then increase. After oxidated at the current density of 9.5A/dm2 for 2min, the oxidation coating quality of gradient porous Mg-Zn alloys of 3wt% Zn is best. The thickness of oxidation coating with uniform pores is 47.5μm. XRD and EDS analysis show that there are MgO and Mg2SiO4 phases in the oxidation coating. Corrosion resistance measurement show the weight loss, amount of hydrogen evolution and change of pH value of gradient porous Mg-Zn alloy after micro-arc oxidation is the least of the three kinds of samples. After micro-arc oxidation, the corrosion resistance of gradient porous Mg-Zn alloy is improved. When Zn element of 3wt% is added in Mg matrix, the corrosion resistance of gradient porous Mg-Zn alloy is best.