Study On The Effect Of Cold Compression Process For Residual Stress Of 7050 Aluminum Alloy Forgings

For the large-scale 7XXX aluminum alloy forgings,usually through the solution heat treatment process to improve it is strength,toughness,corrosion resistance,fatigue and other comprehensive mechanical properties.However,quenching process in the process will introduce a large quenching residual stress,which not only affect the static strength,stress corrosion and fatigue resistance of the material,but also affect the size and shape stability of the subsequent machining of the component.Therefore,how to control and reduce the large-scale aluminum alloy component's quenching residual stress is 7XXX aluminum alloy research and application of a hot spot in nowadays.In order to reduce the residual stress of superfine 7050 aluminum alloy forging,the distribution law of quenching residual stress in forging is studied systematically by means of numerical simulation and process experiment,and to explore the effect and mechanism of the residual stress about the quenched forging.This provides a reference for the production and the reduction of residual stresses of large-scale 7050 aluminum alloy forgings.The main conclusions are drawn as the following:(1)The temperature field and stress field of 7050 aluminum alloy samples were simulated by Deform-3D numerical simulation software,the value and distribution of quenching residual stress were studied and the influence of quenching immerse method on residual stress was studied.Except that,in order to verify the reliability of the finite element simulation analysis,the quenching residual stress of the samples' surface was measured by X-ray diffraction.The results show that there are obvious residual stresses in the quenched specimen,and its distribution is "compressive stress in external and tensile stress in internal".The range of residual stresses ?x,?y and ?z in the length,width and thickness direction are-162 MPa?196MPa,-195MPa?160MPa and-189MPa?56.4MPa,respectively.The quenching immerse method has a great influence on the size and distribution of residual stress.The temperature gradient and the quenching residual stress are the highest when the quenching immerse method with flat,and the temperature gradient and the residual stress are the lowest when the quenching immerse method with vertical.(2)The influence of the segmented cold-pressing method,the piecewise cold-pressing process parameters and the cold-pressing die indenter structure on the quenching residual stress of the 7050 aluminum alloy was studied by the the combination of numerical simulation and experimental study.The results show that the effect of symmetrical fractional cold pressing on the quenching residual stress is better than that of asymmetric section,and the residual stress distribution is more uniform;In the range of 25%?75%feet rate,the residual stress reduction effect decreases with the increase of feed rate.In the range of 0.5%-4%press amount,the effect of residual stress reduction is increast at first and then decreases,and the best reduction effect is 3%;When the radius of the die is R0?R10,the residual stress reduction effect increases with the radius of the die increases.The optimum cold pressing process of the given forging is determined,which the press amount is 3%,the feet rate is 25%and the radius of the die is R10.(3)The numerical simulation method was used to study the temperature field and stress field's evolution of 3200mm × 1200mm×400mm large-scale 7050 aluminum alloy forging during the quench.The value and distribution about the residual stress on the surface of the forging before and after the segmented cold-pressing are compared and analyzed,and the effect of the residual stress on the residual stress is evaluated,and the effect of the residual stress reduction about the segmented cold-pressing process was evaluated.The results show that the surface of the forging can be reduced to quenching medium temperature after 370s,while the core need approximately 800s to reduce the quenching medium temperature;In the process of quenching,the residual stress distribution is changed from the "tensile stress in external and compressive stress in internal" of the initial quenching to the "compressive stress in external and tensile stress in internal" at the end of quenching.The residual normal stress values in the length and width directions are as high as-418MPa?324MPa and-409MPa?341MPa.After the segmented cold-pressing,the residual stress decreases significantly,the above stress values are reduced to-119MP?120MPa and-129MPa?150MPa,the overall degree of reduction about 70.3%to 97.4%.The simulated value of residual stress before cold pressing is 20MPa?50MPa lower than the measured value,and the residual value of residual stress after cold pressure is less than 20MPa.