| Magnesium alloys are currently the lightest metal structural materials,and have the advantages of high specific stiffness,high specific strength,good electromagnetic shielding and shock absorption properties,and are widely used in aviation,aerospace,automotive and other fields.Among them,the Mg-Al system is the most widely used.AZ80 magnesium alloy has been widely used in the automotive wheel industry due to its good strength and corrosion resistance.It is of great significance to strengthen the research on its performance.By compressing AZ80 magnesium alloy at room temperature with small strain and multiple passes,a large strain can be accumulated,so as to generate a fine twin crystal structure and achieve the purpose of fine grain strengthening.In this paper,as-cast AZ80 is selected as the research object,the as-cast samples are first subjected to homogenization treatment at 415?×16h,and then subjected to multi-directional compression at room temperature,each compression in X,Y,and Z directions is recorded as a pass,the compression sequence of each pass is fixed,the strain of one pass is 0.11,a total of four passes of compression deformation are carried out,and the cumulative deformation amount is 0.44.Microscopic analysis samples were cut from the core,the center of the outer surface,and the corners of the samples,and the samples were analyzed by EBSD,XRD,and SEM.Then,the deformed samples were aged at 175°C and 200°C,respectively,to observe the changes of the precipitates at different aging temperatures,and to test the hardness and tensile properties of the deformed and aged states to compare the changes in mechanical properties.Compared with the corners and the core of the outer surface,the core of the deformed sample has the most uniform deformation,the largest number of twins,and the best grain refinement effect,which can clearly reflect the structural changes caused by the deformation of this pass.With the increase of deformation passes,the volume fraction of the twin structure in the core of the sample increases from 0 to 54.6%,and the average grain size decreases from270 ?m in the uniform state to 52 ?m in four passes.During the multidirectional compression deformation at room temperature,the twins increase,the grain refinement is obvious,and the twin boundaries per unit volume increase,which hinders the sliding of dislocations and improves the mechanical properties of the alloy.The hardness value gradually increases with the deformation pass,from 63 HB in the uniform state to 102 HB in four passes,and the tensile properties have the same trend of change.However,the plasticity showed a pass-by-pass decrease,from 10.2% to 1.3% in the homogeneous state.Under the peak aging treatment,the precipitates are all precipitated in the twin crystals in the form of dots and in the form of lamellae on the matrix,but with the prolongation of the aging treatment time,the size of the precipitates will grow to different degrees.Aging treatment at 175°C has the greatest increase in hardness.After 24 hours of aging treatment,the peak age of four passes reaches 116.5HB,but the time required to reach the peak age is longer than that at 200°C.The strength after peak aging at 200°C is slightly higher than the peak aging strength at 175°C,and the difference between the strengths at the two aging temperatures is small.The strength of the sample after aging treatment is lower than that of the deformed shape,the plasticity has not been significantly improved after aging treatment. |
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