Research On Microstructure And Properties Of Mg-xAl-1Sn Alloy

With the rapid development of various industries,the requirements for the comprehensive properties of Mg alloys have also been enhanced.To develop a new non-rare earth Mg alloys with excellent properties.The Mg-x(0,3,6,9)Al-1Sn alloy was fabricated and subjected to solution treated at 415°C,then txtrusion in a speed of 0.1 mm/s at 300°C.The influence of Al content on the microstructure,mechanical properties and corrosion properties of as-solution treated and txtruded alloy was studied,and the influence of current density and Al content on the discharge properties of as-extruded Mg-x(0,3,6,9)Al-1Sn alloy was studied.The research results show that the second phase of the solid solution Mg-xAl-1Sn(x=0,3,6,9 wt.%)alloy is mainly Mg₂Sn and Mg₁₇Al₁₂ phases.And with the increase of Al content,the volume fraction of the precipitates increased significantly.The volume fraction of the second phase of AT91 alloy reached 11.41%,the UTS of the alloy increased from?104 Mpa to?254 Mpa,and the YS increased from?30 Mpa to?112 Mpa,the elongation is about?9%.The main reason is related to solid solution strengthening and precipitation strengthening.In addition,the corrosion rate of Mg-xAl-1Sn alloy are increased with the increase of Al content,and the corrosion pits of Al modified alloy are larger in size and deeper.The galvanic corrosion formed by the Mg₁₇Al₁₂ and Mg₂Sn phases with higher electrode potential and the Mg matrix is the main reason for the rapid corrosion of as-solid solution Mg-xAl-1Sn(x=3,6,9 wt.%)alloy.After subject to extrusion,the results indicated that the dynamic recrystallized(DRXed)grain size of the as-extruded Mg-0Al-1Sn(AT01)alloy was coarse,but the Al modified alloy shows uniform DRXed grain distribution and the grain size decreases accompanied with the increasing of Al content.The average grain size of Mg-9Al-1Sn(AT01)alloy was 2.17?m.Meanwhile,the solid solubility of the Sn element was changed attribute to the addition of the Al element,resulting in the reduction of Sn element dissolved in the matrix,which promotes the precipitation of Mg₂Sn phase,and the volume fraction of the precipitates was increased significantly in the Al modified alloys.The tensile results showed that the ultimate tensile strength(UTS)significantly increased with the increasing Al content.The UTS of AT91 alloy reached to 395.8 Mpa,which was 60.5%higher than that of AT01 alloy.In addition,different corrosion behaviors were shown in the Al modified alloy.On the one hand,a large number of discontinuous Mg₁₇Al₁₂ and strong cathode Mg₂Sn phases were distributed along the grain boundaries,which quickly form galvanic corrosion with the Mg matrix,promoting the dissolution of the Mg matrix.On the other hand,due to the protective film formed in the Al modified alloy was discontinuous and limited,corrosion crosses the grain boundary from one grain to another,accelerating the rapid dissolution of the matrix.Moreover,the decreasing grain size,also accelerates the hydrogen evolution corrosion rate.As the current density increases,the battery voltage of the Mg-xAl-1Sn alloy gradually decreases,and the anode efficiency gradually increases.The increase of Al content increases the battery voltage of Mg-xAl-1Sn alloy at different current densities.AT91 alloy still has a stable battery voltage at relatively high current density.When the current density reaches 20m A·cm^-2,The voltage value of AT91 alloy is still 1.03 V.This is mainly because the refined crystal grains and evenly distributed second phase promote the discharge activity,increase the effective discharge area,and make the generation and dissociation of the discharge products reach a dynamic balance.In addition,a large number of cracks are formed during the discharge process.It has a stable discharge voltage,therefore AT91 alloy is expected to be a candidate for Mg-air batteries.However,the fine grain size with discontinuous precipitates existed in Al modified alloy is beneficial to facilitate the self-peeling of discharge products by forming the micro-cracks on the as-extruded Mg-xAl-1Sn alloy surface during discharge process.The results suggest that the AT91 alloy exhibits a excellent discharge stability at the relatively large current density for long-time.Specifically,the average cell voltage of AT91 anode for Mg-air battery within 5 h at20 m A·cm^-2 was 1.032 V.