Research On Quenching Residual Stress And Cold Pressing Reduction Of Large-size Magnesium Alloy Ring

In order to achieve the required strength,toughness and anti-fatigue performance requirements of aerospace,the Properties of Mg-Gd-Y-Zr-Ag Magnesium Alloy rings used in small and medium-sized rockets are often modulated by solution quenching and subsequent heat treatment.In the process of quenching,a large residual stress will be introduced,resulting in cracking failure of the ring or large processing deformation in the subsequent processing.Therefore,the research on quenching residual stress and the reduction process is beneficial to the development and application of rare earth magnesium alloy in aerospace field.In this paper,the distribution of quenching residual stress of magnesium alloy ring is studied by means of finite element simulation and experiment.And the effect of cold pressing on the reduction of quenching residual stress of magnesium alloy ring was studied by finite element simulation.The main research contents of this paper are as follows:First,the samples of Mg-Gd-Y-Zr-Ag wrought magnesium alloy were taken from Magnesium alloy component.And the samples were used to test thermal and mechanical properties of the material.It provides a basis for establishing an accurate finite element model of magnesium alloy ring quenching residual stress and its cold-pressing reduction.Second,the thermal-mechanical coupling finite element model of magnesium alloy ring quenching is established.The evolution of the quenching temperature field and the distribution law of quenching residual stress of magnesium alloy ring is analyzed.And the influence of quenching process parameters and ring geometry on the distribution of quenching stress field of ring was studied.The research results show that the quenching residual stress of the ring mainly follows the distribution law of "internal tension and external pressure",the quenching water temperature has a great influence on the quenching residual stress,and the water entry speed has a small effect on the quenching residual stress;The quenching residual stress stress field of the ring can be divided into the end region and the stress stable region.When the height-to-width ratio of the ring section is greater than 4,except for the larger proportion of the stress-stable area of the ring,the magnitude and distribution of the stress in these two areas remain basically unchanged.Third,the finite element model of the quenching residual stress of magnesium alloy rings was experimentally verified,and the residual stress on the surface and inside of the workpiece was characterized by the hole-drilling method and the contour method respectively.The test results were in good agreement with the finite element results,which verifies rationality of finite element model for quenching of Mg-Gd-Y-Zr-Ag wrought magnesium alloys in this paper.Fourth,A finite element model for reducing the residual stress of magnesium alloy ring quenching by overall cold pressing and step-by-step cold pressing is established.The effect of overall cold pressing and step-by-step cold pressing on the quenching residual stress were compared and analyzed.And the effects of feed rate,two-step cold pressing and the size of the overlapping area on quenching residual stress reduction effect of magnesium alloy ring were studied.The research results show that both the overall cold pressing and the step cold pressing can reduce the quenching residual stress.For the step-by-step cold pressing,when the reduction is 1.5% and the overlap area is 25%,the reduction effect is the best.At this time,the stress reduction rates of the overlapping area and the non-overlapping area are 82.1% and 57.9%,respectively.And the two-step cold pressing can effectively reduce the stress concentration in the overlapping area.This paper has 66 figures,10 tables,and 69 references.