On Preparation And Properties Of Soluble Magnesium Alloys For Fracturing Ball

Using biodegradable materials to prepare underground temporary plugging tools,not only can reduce the risk of oil production,improve mining efficiency,but also reduce the pollution of oil resources,and is the development trend of underground temporary plugging tools.One of the main components of the temporary plugging tool is the soluble fracturing ball.Magnesium alloys are ideal materials for preparing soluble fracturing balls due to their good mechanical,processing properties and easy dissolution in electrolyte solutions.The research object of this thesis is soluble magnesium alloy.Soluble magnesium alloys were prepared by casting,hot extrusion and subsequent heat treatment.The influence of the types and contents of alloying elements on its mechanical properties and solubility properties was detected by OM,SEM,XRD and electrochemical workstation with mechanical performance test,corrosion weight loss test and electrochemical test.Based on the change of dissolution rate and corrosion film thickness during the dissolution of soluble magnesium alloy,alloy dissolution models were established.The detailed research content and results are as follows:（1）Soluble Mg-Cu-Ni-Zn alloy was prepared by casting and subsequent heat treatment.The microstructure,mechanical properties and solubility of soluble Mg-Cu-Ni-Zn alloy was investigated with the increase of Cu and Ni element content.With the increase of Cu and Ni element content,the second phase Mg₂Cu and Mg₂Ni were continuously distributed in a grid shape and their content also increased.The tensile strength,compressive strength and dissolution rate of the alloy increase at the beginning and then decrease with the increase of Cu and Ni content.When the content of Cu and Ni elements is 4%,the tensile yield strength of the soluble Mg-Cu-Ni-Zn alloy is 95MPa,the tensile strength is 201 MPa,the elongation is 5.7%,and the compressive strength of Mg-Cu-Ni-Zn is 235 MPa at 80°C.The dissolution rate of the materials in3%KCl solution of 30°C is 22.3 mg/（cm²×h）,which meets requirement of soluble fracturing balls for serving-in a range of 30°C to 80°C.（2）Soluble Mg-Y-Zn-Cu-Ni alloy was prepared by casting and subsequent heat treatment.The microstructure,mechanical properties and solubility of the soluble Mg-Y-Zn-Cu-Ni alloy was investigated with increase of Y element content.The second phase in the alloy was LPSO phase which was distributed in block,strip and lamellar shapes.Its content and volume increase with the increase of Y element content.The tensile strength and compressive strength of the soluble Mg-Y-Zn-Cu-Ni alloy increase with the increase of Y content,and the dissolution rate increases at the beginning and then decreases with the increase of Y element content.When the content of Y is 2%,the tensile yield strength of the soluble Mg-Y-Zn-Cu-Ni alloy is 127 MPa,the tensile strength is 215 MPa,the elongation is 6.1%,the compressive strength at 80°C is 329MPa,and the compressive strength at 130°C is 231 MPa.The dissolution rate in 3%KCl solution at 80°C is 23.6 mg/（cm²×h）,which meets requirement of the soluble fractured ball in the service temperature of 80°C to 130°C.（3）By comparing the morphology and thickness of the surface and the thickness of the corrosion film between the soluble Mg-Cu-Ni-Zn alloy and the soluble Mg-Y-Zn-Cu-Ni alloy,the dissolution model of the soluble magnesium alloy was established based on the formation principle of the corrosion film of the magnesium alloy.The type and content of alloying elements will affect the morphology and thickness of the corrosion film on the magnesium alloy surface.At 80℃,after 2 h of dissolution in the3 mass%KCl solution,the surface corrosion film of the soluble Mg-Cu-Ni-Zn alloy is porous,and the film thickness is about 60μm.The corrosion film on the surface of the soluble Mg-Y-Zn-Cu-Ni alloy is relatively dense,and its thickness is about 120μm.