Research On Microstructure And Mechanical Properties Of Mg-Al-Sn Alloy By Asymmetric Severe Shear Extrusion

As one of the lightest metal structural materials,magnesium alloys also have the characteristics of high specific strength/specific stiffness,good thermal conductivity,excellent electromagnetic shielding performance and environmental friendliness while achieving light weight.It has broad application prospects in automobile manufacturing,communication electronics,aerospace and other industrial fields.However,due to the close-packed hexagonal structure of magnesium alloys,there are few independent slip systems that can be activated at room temperature,resulting in poor plastic deformation processing ability,which greatly limits the wide application of deformed magnesium alloys.Based on the existing asymmetric extrusion technology,this study proposes a new asymmetric severe shear extrusion deformation(asymmetric extrusion + severe shear deformation)method.This method uses slab casting,which can achieve greater shear extrusion than traditional round bars.By adjusting the position of the outlet channel of the die to optimize the asymmetric extrusion coefficient,a magnesium alloy sheet with fine structure and excellent performance can be obtained,thereby realizing the low-cost and short-process preparation of high-strength and tough magnesium alloy.Taking AT41 magnesium alloy as the research object,adding different contents of Ca element,the effect of Ca element on the asymmetric extrusion microstructure,texture and mechanical properties was studied.At the same time,the microstructure,grain orientation and mechanical properties of three kinds of extruded sheets with different asymmetric coefficients are mainly studied,and the deformation mechanism of structure and texture is deeply analyzed.The main research contents and results are as follows:(1)Taking AZ31 magnesium alloy as an example,the deformation mechanism of asymmetric severe shear extrusion was revealed through the DEFORM-3D finite element simulation software.The effects of different asymmetric coefficients on the metal flow regularity and the distribution regularity of effective stress,strain and velocity fields during asymmetric severe shear extrusion deformation of magnesium alloys are mainly studied.The asymmetrical severe shear extrusion deformation causes the effective stress,effective strain and flow velocity field of the metal in the cavity to be asymmetrically distributed due to the deviation of the die outlet channel from the center line,which can increase the effective strain and flow velocity,while improving the metal mobility.The rightward shift of the outlet channel of the asymmetric extrusion cavity causes the metal flow velocity and effective strain on the right side of the extruded sheet to be greater than that on the left side.The results show that the AC-1.5 sheet has the severest effective strain and the most uniform distribution.(2)By adding different contents of Ca to AT41 magnesium alloy,the effects of different contents of Ca on the microstructure and properties of as-cast and asymmetric severe shear extrusion were studied.After adding different contents of Ca,different second phase types appeared due to the change of Sn/Ca.With the increase of Ca content,the number of second phases increases,the as-cast microstructure is refined to a certain extent,the yield strength does not change significantly,and the elongation decreases.However,after asymmetric severe shear extrusion,the second phase is obviously refined and distributed along the ED direction,and the grains are refined by the PSN mechanism.The yield strength of ATX4104 magnesium alloy reaches 198 Mpa and the elongation reaches 21%.The comprehensive mechanical properties are best.(3)The effects of extrusion with different asymmetric coefficients on the microstructure,microstructure evolution and mechanical properties of ATX4104 magnesium alloy sheets were systematically analyzed,and the microstructure evolution regularity and forming mechanism of the extrusion process were explored.Compared with symmetric extrusion,the metal is subjected to additional shearing action during asymmetric severe shear extrusion deformation,which can significantly refine the grain size of ATX4104 magnesium alloy and weaken the texture.The ATX4104 magnesium alloy sheet with asymmetric coefficient AC=1.5 has the smallest microstructure(8.6 ?m)and the weakest texture(Max: 5.25).Under the combined effect of grain size and texture,AC-1.5 magnesium alloy sheet exhibits the best mechanical properties(175.9 Mpa,19%)and formability.There are microstructure and texture gradients in the width direction of the sheet after asymmetric severe shear extrusion deformation,and the mechanical properties are also quite different.Among them,the average grain size on the right side of the extruded sheet is the smallest,the texture is the weakest,and the yield strength and elongation are higher.