Study On Mechanical Properties And Microstructure Of Mg-3Al-1Sn-1Zn Magnesium Alloy Under Pulse Current

Magnesium alloy is the lightest engineering alloy,and have good application prospects in the fields of vehicle transportation,medical equipment,national defense industry and communications electronics.However,the engineering application of magnesium alloys are limited by some defects such as poor plasticity at room temperature and high processing costs.Studies have shown that the application of pulse current during the forming process of magnesium alloy can effectively reduce its flow stress and improve its formability.Compared with the warm forming,this method is more efficient and energy-saving,which greatly reduces the processing cost.This makes it possible for Electroplastic assisted processing to replace traditional thermal processing.At present,there are still lack of research on the influence of pulse current on the microstructure and its mechanism.The theoretical basis for the application of pulse current to engineering practice is relatively weak.The above factors hinder the application and development of electroplastic processing technology.In view of the above problems,this paper explores the mechanical properties and microstructure of Mg-3Al-1Sn-1Zn(ATZ311)magnesium alloy based on the pulse current-assisted uniaxial tensile test,and reveals the influence of pulse current on mechanical properties and microstructure;and establish the connection between mechanical properties and microstructure,further reveal the microscopic mechanism of plastic change under pulse current;At the same time,by studying the dynamic recrystallization behavior of pre-existing ATZ311 magnesium alloy under pulse current,The twin-induced dynamic recrystallization under pulse current is revealed.The main conclusions reached are:(1)When electrically-assisted tensile test,the tensile strength and elongation of ATZ311 magnesium alloy specimens are inconsistent with the change of peak current density:the tensile strength shows a gradual decrease trend,from?264 MPa at 0 A/mm~2to?52 MPa at 50 A/mm~2;the elongation first increases and then decreases.When the peak current density is 30 A/mm~2,the elongation is the largest(??36%).(2)Pulse current will affect the microstructure of ATZ311 magnesium alloy:When the peak current density is 20 A/mm~2,since no obvious dynamic recrystallization occurs,the grains are relatively coarse and the texture strength is relatively large;When the peak current density is 30 and 40 A/mm~2,significant dynamic recrystallization occurs,and the grains are refined to?15?m and?20?m,respectively,and the texture is also weakened to 10.3 and 5.2 respectively;When the peak current density is 50 A/mm~2,the input energy is higher,which promotes the growth of DRX grains.The average grain size increases to?53?m,and the texture strength is also increased to 16.6.(3)Under different peak current densities,the deformation mechanism and dynamic recrystallization mechanism of ATZ311 magnesium alloy are different.Deformation mechanism:slip and twin at low peak current density(20 A/mm~2);when the peak current density increases to 30 A/mm~2,at the early stage of deformation(?<16%),it is mainly slip and twin,and in the later period,it changes to slip;when the peak current density continues to increase(40 A/mm~2,50 A/mm~2),slip is dominant.Dynamic recrystallization mechanism:When the peak current density is 30 A/mm~2,continuous dynamic recrystallization is dominant;when the peak current density is 40,50 A/mm~2,continuous dynamic recrystallization and discontinuous dynamic recrystallization occur simultaneously.(4)The plasticity change of ATZ311 magnesium alloy under pulse current is determined by many factors.After the peak current density reaches a certain value(?30 A/mm~2),the non-basal surface slip of ATZ311 magnesium alloy is activated,and dynamic recrystallization occurs at the same time,thereby promoting plastic deformation.However,when a pulse current with a larger peak current density(40A/mm~2,50 A/mm~2)is applied,the sample will enter the uneven deformation stage earlier,and the deformation will be limited to the necking area;in addition,the temperature at later stretch is higher,this will cause the deterioration of the structure(grain growth),and even partial melting.These two points lead to a decrease in elongation when compared to 30 A/mm~2 at high peak current density.(5)The microstructure of the pre-existing ATZ311 magnesium alloy has similar changes in electrically-assisted tensile test and high temperature tensile test,the recrystallization fraction gradually increases,and the twin fraction gradually decreases;obvious DRX grains are observed at the double twins and contraction twins,but not at the tension twins.In addition,dynamic recrystallization occurs in electrically-assisted tensile test at 5%strain,but not occur at this strain in high-temperature tensile test.It is speculated that this is caused by the pure electroplastic effect in the pulse current.