Effect Of Multidirectional Forging On Microstructure And Properties Of AZ40 Alloy

With the exploitation and exhaustion of conventional oil-gas resources,Unconventional oil and gas resources such as shale oil and gas will become an important alternative to oil and gas energy in the future.Horizontal Well Staged Fracturing Technology is a mature technology for the exploitation of this type of oil and gas resources at home and abroad.Bridge plug is an important part of this technology,among which the new soluble bridge plug has become a research hotspot due to its advantages of self-dissolving and increasing working efficiency.Except the expansion tube is made of soluble rubber,the rest of the new soluble bridge plug is made of magnesium alloy.Soluble rubber material not only dissolves slowly,easily causes secondary blockage,but also tends to rebound and fail during the operation of the bridge plug.Using magnesium alloy instead of soluble rubber material can not only achieve the synchronous degradation of the bridge plug,but also avoid the consequence of the rebound of soluble rubber and the failure of the bridge plug.However,due to its strong substrate texture,the extruded magnesium alloy exhibits significant anisotropy.Therefore,improving the radial plasticity of magnesium alloy has become the key to the application of magnesium alloy in expand tube.In this paper,the extruded AZ40 alloy was used as the experimental material.After multi-directional forging,the extruded alloy after different times of forging were studied through OM,EBSD,SEM and room temperature mechanical properties test,especially the evolution process of texture.In addition,the development law of magnesium alloy was summarized,and the key mechanism was explored to provide experimental data and theoretical basis for improving the radial plasticity of magnesium alloyThe flow stress of the alloy were obtained by thermal simulation experiments,showing obvious dynamic recrystallization characteristics.The modified constitutive equation based on the Arrhenius model was obtained from the decrease of peak stress with deformation temperature and the change of strain rate,and the accuracy of the constitutive equation was verified.Through the construction of hot working diagram and microstructure analysis,the optimal forging process is obtained as T=300?(573K),?=0.1 s-1?Different times of multi-direction forging experiments were carried out on extruded AZ40 alloy.After forging,the samples were analyzed by metallography and EBSD,and it was found that the extruded alloy had obvious streamline structure along the ED direction,and had strong basal texture.After two times of forging,the alloy underwent dynamic recrystallization,grain size refined,small angle grain boundary increased,texture deflected,strength decreased and base plane texture weakened.After four times of forging,the large angle grain boundaries of the alloy increase,and the grains continue to rotate under the action of external forces,forming {1010} and {2110} texture.After six times of forging,the grain size tends to grow,the grain size was more uniform,the grain orientation was more random,and the texture was diffused.The grain rotation mechanism was studied by the evolution of texture during forging process.Through the test of the mechanical properties of the alloy,it is found that the mechanical properties of the extruded alloy have significant anisotropy.Especially,the difference between yield strength and elongation is obvious.With the progress of multi-direction forging,the yield strength of the alloy decreases obviously compared with the extruded state,the elongation increases,and the anisotropy of mechanical properties weakens.After four times of forging,the elongation of each surface of the alloy reaches the maximum value,which coincides with the evolution of texture.By observing the microstructure and morphology of the fracture,it can be concluded that the tensile fracture of the alloy is ductile fracture,with dimples and tearing edges distributed at the fracture.The number of dimples in tensile fracture after 4 times of forging is the largest and the dimples are deeper,which is consistent with the results of mechanical properties of the alloy.