Study On Microstructures And Properties Of AZ80 Magnesium Alloys With Different Volumes Of Precipitates At Grain Boundaries

Magnesium alloy is the lightest structural metal material in application.It has many advantages,such as low density,high specific strength,good damping performance,excellent electromagnetic shielding and so on.It is widely used in aerospace,automobile and other industries.The plastic formability of magnesium alloys is poor at room temperature,due to its close-packed hexagonal structure and lack of sufficient independent slip systems.There are many problems in magnesium alloys produced by traditional production technologies,such as long process flow,low yield,low mechanical property and formability.So the development of wrought magnesium alloy is limited.Therefore,it is of great significance to study the structure of magnesium alloys in order to improve plasticity and promote the application of magnesium alloys.AZ80 magnesium alloy is of high strength and of low cost,but a large number of ?-Mg₁₇Al₁₂ can reduce its deformation ability greatly.So,It is of great significance to improve the plasticity of AZ80 magnesium alloys by studying the volume of ? at grain boundaries.The effects of Mg₁₇Al₁₂ at grain boundaries on the microstructure and room temperature mechanical properties of rolled AZ80 were investigated by making use of optical microscope,XRD,EBSD,TEM,tensile properties test at room temperature.AZ80 were respectively aged for 0min 30 min,75min,160 min,120min,200 min,240min at 175 ? in order to obtain different volume of ? precipitates at grain boundaries.The volume fraction were 1.5%?5%?8%?14%?25%?36%?46% respectively.The aged AZ80 plates were rolled at 350 ? and then annealed for 1h at 175 ?.Then,the microstructure and mechanical properties of as-rolled and as-annealed samples were measured.Processing the data to get the Schmidt factor?m?of?0001?basal slip,{10 ???0}prismatic slip,{10 ???1} pyramidal slip,{11???2}pyramidal slip and orientation distribution of basal slip by taking advantage of EBSD and channel5.The experimental results showed that the mechanical properties of the as-rolled AZ80 can be improved by Mg₁₇Al₁₂ precipitates at grain boundaries,and texture was also weakened.The mechanical properties of as-rolled AZ80 was decreased with the increase of ? precipitates at grain boundaries.When volume fraction was 36%,the performance of as-rolled AZ80 plate was the best.The tensile strength,yield strength,elongation and texture strength were 363 MPa,285MPa,15.4%,4.954 respectively.The strength of texture was the weakest,which was lower than that of extruded AZ80 by 50.63%.The strength of as-annealed AZ80 increased first and then decreased with the increase of ? precipitates at grain boundaries.The strength and plasticity were enhanced compared with the rolled-state.The tensile strength,yield strength,elongation and the strength of texture as-annealed AZ80 were 377 Mpa,315MPa,16% and 7.2 respectively when volume fraction was 36%.The strength of texture was the lowest.SEM showed that discoid ? were broken and dispersed near the grain boundaries during rolling,and a large number of ? particles were precipitated at twin boundaries.With increase of precipitates at the grain boundaries,grains were refined,and there were a large number of small grains around the precipitates.This was mainly due to the dynamic recrystallization of AZ80 during hot rolling.The fine disperse precipitates distributed at grain boundaries.They accelerated the grain refinement and changed the crystal orientation simultaneously.The precipitates were broken and also produced a large number of defects at the same time.They provided address for the nucleation of new grains.TEM shows the distribution of dislocations and trajectories around the precipitates.Dislocation stopped moving near the ? phases or continued exercising after cutting or bypassing the ? phases.With increases of ? at the grain boundaries,the m value of?0001?basal slip of asrolled AZ80 in TD-RD increased significantly.The m value of {10???0} prismatic slip was lower slightly.The m value of {10???1} pyramidal slip changed a little.It decreased first and then increased overall,but the {11???2} pyramidal slip was the opposite.The m of?0001?basal slip,{10???0} prismatic slip,{10???1} pyramidal slip,{11???2} pyramidal slip of as-annealed AZ80 were not affected by the volume of precipitates at grain boundaries.The m value of?0001?basal slip and {10???1} pyramidal slip system of asannealed AZ80 was decreased.The m value of {10???0}prismatic slip and {11???2} pyramidal slip was increased.