Effect Of Extrusion And Annealing Processes On Microstructure And Properties Of Mg-Al-Ca-Mn-Cu-Ni Soluble Magnesium Alloys

Soluble alloy is a kind of structure-function integrated material with metal properties and rapid dissolution under certain environment.The bridge plug and temporary plug ball made of soluble alloy can avoid the costly and inefficient manual elimination process and eliminate the possibility of pipeline plugging,so it has a broad application prospect in shale oil and gas exploration field.Magnesium alloy has the characteristics of low density,high specific strength/specific stiffness,low electrode potential,easy corrosion,and has the characteristics of both structural and functional materials,making it the first choice for soluble materials.At present,the research on the strengthening and toughening mechanism and corrosion theory of deformed soluble magnesium alloys has not been in-depth,especially the influence of grain size and second equivalence on the material dissolution mechanism has not been able to guide the design and preparation of high-performance soluble magnesium alloys.In this paper,a Mg-0.34Al-0.24Ca-0.3Mn-0.2Cu-0.2Ni soluble magnesium alloy material was prepared by adding a small amount of Cu and Ni on the basis of low-cost and high-speed extruded AXM magnesium alloy.Firstly,the alloy was smelted in Muffle furnace under the protection of CO₂+SF₆ atmosphere.Then the samples of different processes were prepared by an 800 ton extruder and a resistance furnace.The mechanical properties and hardness of the materials were tested by electronic universal testing machine and Brinell hardness tester.The dissolution rate and hydrogen evolution rate in93?,3wt.%KCl solution were measured by immersion weightloss experiment and hydrogen evolution experiment.The electrochemical data,such as open-circuit voltage and Tafel polarization curve,were measured by electrochemical workstation.The microstructure,texture and corrosion morphology of the samples were observed by optical microscope,scanning electron microscope,EBSD and X-ray diffraction.By studying the effects of different extrusion temperatures(300?,350?,400?),extrusion ratio(30,60)and heat treatment(500?hold for 12 h,24 h,48 h)on the microstructure and properties of the materials,the following conclusions are drawn:(1)With the increase of extrusion temperature,the dynamic recrystallization occurs more fully,and the average grain size gradually increases from 1.5?m to 3.1?m.The tensile strength increased from 202.8 MPa to 273.6 MPa;The basal texture strength decreases first and then increases,which leads to the elongation increases first and then decreases.The dissolution rate of the extruding sample at 300?was the highest,which was 20.46mg/h/cm².(2)With the increase of the extrusion ratio,the average grain size and texture strength increase,the tensile strength decreases from 244.5 MPa to 236.5 MPa,and the elongation increases from 22%to 26%.The dissolution rate increased from 15.47mg/h/cm² to 17.76 mg/h/cm².(3)With the increase of annealing time,the average grain grows up gradually and increases to 42?m at 500?48h.The yield strength and tensile strength decreased gradually,and the tensile strength decreased from 287.0 MPa to 186.3MPa.The weight loss and corrosion rate of hydrogen evolution increase with the increase of annealing time.In addition,the weight loss test also shows that the corrosion rate of soluble magnesium alloy increases rapidly with the prolongation of immersion time,and then tends to be stable.The surface of the sample showed uniform electrochemical spalling corrosion characteristics.Although the electrochemical corrosion current value of soluble magnesium alloy at room temperature is similar to that of AZ31,its anode slope is only about one-tenth of that of AZ31,so it can reach the steady-state soluble state faster,and its dissolution rate is more than 40 times that of AZ31.