Experimental Research On Mechanical Properties And Corrosion Behavior Of Dissolvable Mg-xAl-yZn-0.2Ni-0.1Mn Alloy

With the development of science and technology,the society’s demand for materials has become increasingly diversified,and structural/functional integrated materials with two or even multiple functions have gradually emerged.As a structure/function integrated material,dissolvable magnesium alloy has certain mechanical properties and at the same time converts the shortcoming of low corrosion resistance into the advantage of rapid and environment-friendly dissolution.It has broad application prospects in the marine and petroleum industry.However,the mechanical properties of the existing dissolvable magnesium alloys are not well matched with the corrosion rate,and the problems of low strength,insufficient plasticity,low corrosion rate and severe local corrosion have hindered the further application and promotion of dissolvable magnesium alloys.In this paper,on the basis of Mg-Al-Zn alloy,Ni and Mn elements are added to prepare Mg-x Al-y Zn-0.2Ni-0.1Mn alloy.Through composition adjustment,homogenization annealing and extrusion deformation,a novel dissolvable magnesium alloy with excellent mechanical properties,high corrosion rate and relatively uniform corrosion is obtained and its microstructure,mechanical properties and corrosion behavior in different states are studied.The study shows that the as-cast structure of the Mg-8Al-1Zn-0.2Ni-0.1Mn alloy is relatively coarse,the second phaseβ-Mg₁₇Al₁₂ is in a network shape and is continuously distributed at the grain boundaries.The as-cast Mg-8Al-1Zn-0.2Ni-0.1Mn alloy has poor mechanical properties,with low hardness and yield strength,which are 42.8 HV and 95 MPa,respectively,and the tensile strength and elongation are 172 MPa and 3.5%separately.With revealing serious local corrosion,the as-cast alloy corrosion rate is as slow as only 3.2 mg/（cm²·h）.After homogenization at 415℃×20 h,the second phase has almost dissolved and the uniformity of structure and composition improved.The mechanical properties are ameliorated,the hardness is increased to 53.3HV,the tensile strength is increased to 235 MPa,and the elongation is increases to 8.1%.The alloy corrosion rate increases,the self-corrosion potential moves negatively,the self-corrosion current increases,the film resistance and the charge transfer resistance decrease,and the corrosion weight loss rate increases.When corroded in a 1%KCl solution at 25℃for 24 h,the average corrosion weight loss rate of the homogenized alloy reaches 4.0 mg/（cm²·h）,which is 25%higher than that of the as-cast alloy.After hot extrusion deformation at 350℃,the Mg-8Al-1Zn-0.2Ni-0.1Mn alloy undergoes complete dynamic recrystallization,and the average grain size is about 24.4μm.During the extrusion process,the second phase precipitates out of the matrix,the quantity increases,their distribution is more diffuse with a reduced average size.Compared with the homogenized alloy,the mechanical properties of the as-extruded alloy are improved,and the hardness,yield strength and tensile strength are increased by 43%,146%and 46%respectively,reaching 76.1 HV,236MPa and 343 MPa,and the elongation increased by 30%,reaching 10.5%.The self-corrosion potential of the alloy becomes positive,the self-corrosion current density decreases,the capacitive impedance arc diameter in electrochemical impedance spectroscopy increases,and the corrosion rate decreases slightly.When corrosion in 1%KCl solution at 25℃for 24h,the corrosion weight loss rate of the alloy is 3.7 mg/（cm²·h）.The decrease of Al content makes the as-extruded Mg-x Al-1Zn-0.2Ni-0.1Mn alloy grain refinement,a new square plate-shaped second phase Al₈Mn₅ phase is formed in the alloy,and the distribution is more uniform.After the Al content is reduced,the hardness of the alloy decreases to 60.7 HV,the tensile strength decreases to 333 MPa,and the yield strength decreases to 218 MPa,but the plasticity increases,and the elongation increases to 21.3%;the self-corrosion potential of the alloy moves negatively,and the self-corrosion current density increases,the capacitive reactance arc diameter in electrochemical impedance spectroscopy decreases,and the corrosion rate of the alloy increases.When corrosion in 1%KCl solution at 25℃for 24 h,the average corrosion weight loss rate is 3.9 mg/（cm²·h）.With the reduction of Zn content,the inhomogeneity of the oxide film on the surface of the as-extruded Mg-8Al-y Zn-0.2Ni-0.1Mn alloy results in an obvious preferential corrosion area on the alloy surface,and the corrosion product Mg（OH）₂ accumulates on the surface of the alloy to form new corrosion products film,which inhibits corrosion.The hardness of the as-extruded Mg-8Al-0.5Zn-0.2Ni-0.1Mn alloy is 65.6 HV,the tensile strength is 319 MPa,the yield strength is 228 MPa,and the elongation is15.5%.When the Zn content decreases,the self-corrosion potential of the alloy moves positively,the self-corrosion current density decreases,and the corrosion rate decreases.The whole article contains 46 figures,26 tables,and 120 references are cited...