Effect Of Microalloying And Grain Boundary Structure On Anisotropy Of Mechanical Properties Of Al-Mg Alloy

Al-Mg-Mn-Sc-Zr alloy not only has the advantages of Al-Mg alloy,but also has higher strength.Al-Mg-Sc-Zr alloy with high Mg content has a broader application prospect in the field of aerospace.However,the anisotropy of mechanical properties of Al-Mg-Mn-Sc-Zr alloy sheet is outstanding,which is disadvantageous to the application of alloy sheets.Therefore,the effect mechanism of Mg content on the anisotropic behavior of Al-Mg alloy sheets was analyzed and discussed.The grain boundary structure of the alloy has been changed by multi-directional forging and annealing treatment.And effect of grain boundary structure on microstructure uniformity and property anisotropy of high Mg content Al-Mg-Mn-Sc-Zr alloy sheet was studied.The results show that:(1)When the content of Mg in Al-Mg alloy increases from 1%to 5%(wt.%),the grain size decreases from 400μm to 280μm,and the stacking fault energy decreases from 96.4m J/m~2 to 32.6 m J/m~2.When the rolling deformation is the same,the shear band density and dislocation density of alloy sheets increase with the increase of Mg content.When the rolling deformation increases,the intragranular shear bands pass through the grain boundary and connect with the adjacent intragranular shear band with the same orientation,and then develops into macroscopic shear bands.The dislocation density of the alloy sheets also increases.In the process of rolling deformation,the other orientations in the alloy sheet gradually turn to Brass and S texture orientation,resulting in the increase of Brass and S texture strength.(2)Due to the influence of shear bands and deformation textures,Al-Mg alloy sheets show obvious anisotropy of mechanical properties.The yield strength and tensile strength of the plate are the highest in 90°direction and the lowest in 45°and 60°direction.The anisotropy of alloy sheets becomes more obvious with the increase of Mg content and rolling deformation.(3)The microstructure of homogenized Al-Mg-Mn-Sc-Zr alloy is mainly equiaxed grains with high angle grain boundaries.The distribution of grain orientation is not uniform,and many grains with Copper,Brass and other orientations are locally continuously distributed.The grains are refined and the grain boundary density increases with annealing treatment of Al-Mg-Mn-Sc-Zr alloy forgings.Currently,the equiaxed grain structure of the high angle grain boundary is transformed into the mixed grain structure with the coexistence of high angle grain boundary and low angle grain boundary.The driving force of recovery and recrystallization increases with the increase of annealing temperature from 300℃to 550℃.The Copper and Brass oriented grains of alloy forgings decrease,the Cube oriented grains increase,and the proportion of recrystallized structure increased to 52.4%.(4)Many shear bands are formed inside Al-Mg-Mn-Sc-Zr alloy sheets in the process of rolling deformation.The strength of Copper,Brass and S texture increases significantly with the increase of rolling deformation.When the rolling deformation is 70%,the maximum strength of rolling deformation texture is 11.3.However,no obvious shear band was observed in the microstructure of the alloy forgings after rolling deformation,and the texture strength decreased obviously.(5)The property of Al-Mg-Mn-Sc-Zr alloy sheets shows significant anisotropy,and the anisotropy becomes more obvious with the increase of deformation.However,the mixed grain structure with high/low angle grain boundary can inhibit the formation of shear band and reduce the texture strength of rolling deformation,which can effectively reduce the anisotropy of mechanical properties of alloy rolled sheets.The IPAYS index and IPAUTS index of the alloy samples annealed at 400℃/1 h are the lowest,and the anisotropy of mechanical properties is the best.