Effect Of Zr On Cracking Of 7020 Aluminum Alloy Casting And Rolling Plate And Its Homogenization Treatment

7020 aluminum alloy with moderate strength,excellent thermal deformation and stress corrosion resistance and good welding performance,widely used in aircraft,ships,rail trains and other means of transport.Increasing the strength of the 7020 aluminum alloy and reducing cracks in the casting process are the future directions of the 7020 series aluminum alloy.Meanwhile,the advantages of the short roll process and high efficiency and energy saving of the twin roll casting process will also become a potential preparation.In this paper,a two-roll casting process successfully prepared a thickness of 2mm Zr content of 7020 aluminum alloy cast-rolled plate,by changing the content of trace elements Zr to reduce the cracks in the casting process.At the same time,the thickness of 2mm 0.53%Zr 7020 aluminum alloy cast-rolled plate was homogenized and aging treatment to further improve the cast-rolled sheet of the performance indicators.Through the above research shows that:?1?Addition of alloying element Zr can effectively improve microstructure and grain refinement of the as-cast 7070 alloy.When the Zr content reaches 0.33%,the grain is the best and the tensile strength and elongation of the alloy are the best.Tensile strength increased by 12%with 0.13%Zr,elongation increased by 108%.?2?With the increase of Zr content,the number of cracks in castings decreases first and then increases.Because the alloying element Zr in the 7020 alloy in addition to part of the solid solution in the Al matrix,the remaining in the form of Al₃Zr play a role in heterogeneous nucleation.Grain refinement of alloyed rolling grain structure,so that when the Zr content reaches a certain value,the pinning in the grain boundary,played to ease the grain boundary dislocation accumulation caused by stress concentration,delay the generation and expansion of cracks,Thereby increasing the mechanical properties of the material and reducing the cracks.When the Zr content continues to increase,some coarse and coarse phases will be collected.These phases do not play the role of grain refinement,but rather become potential causes of crack formation.?3?The second phase in the grain boundary of 7020 aluminum alloy is mainly composed of MgZn2 and Al3 Zr phases.The Al element is uniformly distributed in most of the matrix.The Zn elements mainly concentrate on the grain boundaries with some uneven distribution;Mg elements are mainly distributed on the grain boundaries,and there is a tendency of aggregation.In 7020 aluminum alloy cast-rolled plate with0.53%Zr content,the distribution of the main alloying elements has some nonuniformity,in which the Zr element is at the grain boundary Poly is the most obvious.?4?In the RRA heat treatment,the regression temperature has a great influence on the precipitation of the phase.The best regression re-treatment process is 120?×24h+160?×2h+120?×24h,the tensile strength of the material can reach250 MPa,The hardness was 181 HV,the conductivity was 36.6%IACS and the elongation was 11.12%.?5?In the homogenization temperature of 440?/8h+340?/8h+470?/8h,the aging temperature of 120?×24h+160?×2h+120?×24h,the best mechanical properties of sheet metal,sheet plasticity and Conductivity is also the best,because after the aging treatment,the regression temperature of 160?,the precipitation of the second phase particles up to and dispersion,while the rare residual phase reduces the stress concentration in the sample,the sample of Best mechanical properties.