| Magnesium alloys were widely used in aviation,aerospace,military and civil fields due to their excellent physical and mechanical properties.At present,there are many reports on the study of serve plastic deformation technologies of wrought magnesium alloys,but most of the serve plastic deformation technologies have some problems such as low production efficiency,high cost,complex process and can not realize continuous production.This paper presents a new technology named rod-plate direct extrusion and bending shearing composite continuous forming(DEBS),which is composed of forward extrusion and multiple bending shear.The research material is commercial cast magnesium alloy AZ31,the process has been studied in many aspects by using the theory of plastic mechanics calculation,finite element numerical simulation and experiment methods,including theoretical calculation of the extrusion load,strain and strain rate,design of the die cavity and process parameters optimization,DEBS magnesium plate mechanical properties and microstructure detection and analysis and so on.The results obtained are as follows:(1)Theoretical analysis of DEBS composite forming process.We calculated the extrusion load,the strain,strain rate and deformation rate factor(Z parameters)of DEBS process by combining upper bound method with the finite element numerical simulation,introducing the complicated shape coefficient.The reliability of the calculation results was verified by experimental study,which can provide a theoretical guidance for the design of the die cavity and the reasonable selection of the extrusion equipment.(2)The design of DEBS die cavity.The average of extrusion load Favg and velocity field relative standard deviation VRSDV,strain ?avg and strain relative standard deviation ?RSDV were taken as the quantitative evaluation indexes,by using the finite element numerical simulation software DEFORM-3D to simulate the extrusion process of DEBS and abtained the effects of the structural parameters on the forming results.The results show that we can get magnesium alloy plate(cross section: 25 mm * 3 mm)of good quality througth the DEBS composite extrusion process when the taper angle ?,bending angle of extrusion channel ? and ?,transition radiu of extrusion channel R1,sizing length L5 is 120o,150o,110o,6 mm and 12 mm respectively.(3)Optimization of DEBS process parameters.Selecting the DEBS die has been designed as the basis for research,by using the finite element numerical simulation software to simulate the extrusion process of DEBS under different process conditions,and studied the effects of the process parameters on the forming results.The results show that the quality ofthe plate can be ensured when the extrusion temperature T,extrusion speed V is 370 ? and 2mm·s-1respectively.(4)Experimental verification and analysis.The DEBS extrusion test was successfully carried out under the guidance of the numerical simulation results,and the mechanical properties and microstructure of DEBS magnesium plate were tested and analyzed.The results show that the microstructure and mechanical properties of magnesium alloy can be significantly improved by DEBS composite process.When the extrusion temperature T and extrusion speed V is 370 ? and 2 mm·s-1 respectively,after once forming the average grain size of the original cast can be refined from 240 ?m to 6 ?m,while the tensile strength and yield strength can reach to 300 MPa and 220 MPa respectively,room temperature elongation rate can reach 25.7%,which also verified the rationality results of DEBS process parameter optimization analysis.The comparison between the measured values and the numerical simulation shows that the relative error is less than 10%,which can meet the requirements of engineering calculation and verify the reliability results of the numerical simulation. |
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