| 7050 aluminum alloy has high strength,high toughness,corrosion resistance,high hardenability and other performance advantages.It has important application value and broad application prospects in the fields of avi ation,aerospace,defense industry and transportation.Studies have shown that the 7000 series aluminum alloy with fibrous grain structure and low angle grain boundaries has better strength,fracture toughness and corrosion resistance.Therefore,how to ob tain high volume fraction low angle grain boundaries and incomplete recrystallization deformation structure is the key to improving the overall performance of the alloy.The results of thermal simulation of 7000 series aluminum alloy show that increasing t he strain rate can effectively inhibit the recrystallization of the alloy and obta in the fibrous grain structure.Aging heat treatment is the main method to improve the toughness and corrosion resistance of 7000 series alloys,but the influence of low angle grain boundaries on the aging behavior and properties of alloys is still unknown.The paper selects 7050 aluminum alloy as the research object,adopts high strain rate rolling（HSRR）to prepare alloy plates,and regulates the grain structure characteristics of the plates;uses solution treatment,single-stage aging,double-stage aging and regression re-aging to control the alloy characteristics of the second phase（type,distribution and volume fraction）,explore the recrystallization law and dynamic precipitation behavior of the alloy during HSRR,the effect of the high strain rate rolling structure on the solid solution and aging behavior of the alloy,and the subgrains and precipitation affect the mechanical properties and corrosion resistance of the alloy.The main research content and conclusions of the paper are as follows:（1）The effects of rolling temperature（370℃,400℃,430℃,460℃）and strain rate(10s-1,20s-1)on the dynamic recrystallization behavior of 7050 aluminum alloy and the dynamic precipitation behavior of precipitates are c larified.It is found that HSRR can obtain low angle grain boundaries with high volume fraction,which increases with the increase of strain rate,but decreases with the increase of rolling temperature.When the rolling process parameter is 370℃/20s-1,the low angle grain boundary ratio is as high as 95.64%.（2）A high-density fine second phase is dynamically precipitated during HSRR,with a size between 25 and 30 nm.The size of the precipitates decreases with the increase of strain rate.After the nano-scale dynamic precipitates is solid-solution treated at 470℃/0.5h,an ideal solid solution effect can be obtained.The morphology of the crystal grains after short-term solution treatment is still fibrous,but a large number of subgrains are formed.（3）After the extruded slab is rolled at 400℃/20s-1high strain rate and short-time solution treatment,it is subjected to peak aging at 120℃/24h（T6 state）,and the alloy has a tensile strength of 622MPa and yield strength.It reaches 540MPa,and the elongation after fracture reaches 20.57%.The main strengthening mechanism of the alloy is precipitation strengthening and subgrain strengthening.（4）After high strain rate rolled plates are treated with T76（120℃/6h+163℃/12h）and T74（120℃/6h+163℃/24h）aging treatments,the corrosion resistance of the alloy has been significantly improved.The exfoliation corrosion ratings of T76 and T74 are EB and EA,respectively,and the ratings of intergranular corrosion are 3 and 2,respectively;the strength of the alloy decreases slightly,the tensile strength of T76and T74 are 597 MPa and 576 MPa,respectively,and the yield strength is 537 MPa and 515 MPa,respectively.The elongation also has a certain decrease,the elongation after break of T76 and T74 are 15.54%and 13.66%,respectively.（5）The optimal regression and re-aging process parameters are optimized,which is 120℃/24h+190℃/0.5h+120℃/24h.The mechanical properties of the sample are higher than that of the two-stage aging,and the tensile strength i s 614MPa,yield strength of 561MPa,elongation after fracture 16.11%,corrosion resistance has also been improved,the exfoliation corrosion rating is EB,and the intergranular corrosion rating is 3.The characteristics of the intragranular precipitates after the regression and reaging treatment are similar to T6,and the characteristics of the grain boundary precipitates are similar to T76.Therefore,the sheet after the regression and reaging treatment has mechanical properties equivalent to T6 state and corrosion resistance equivalent to T76 state. |
