Effect Of Cryogenic Treatment On Precipitation Hardening And Corrosion Resistance Of 7050 Aluminum Alloy

The effect of cryogenic treatment on precipitation hardening and corrosion resistance of T6 and T74 state 7050 aluminum alloy were mainly studied in this paper.Mechanical properties test,potentiodynamic polarization test,intergranular corrosion test and SSRT test were made to T6 state and T74 state 7050 aluminum alloy.The intragranular precipitation phase and the vicinity of the grain boundary of 7050 aluminum alloy under different heat treatment conditions were observed by TEM.EDS line scanning was performed on the grain boundary and its vicinity.Semi-quantitative study The distribution of the phase and the nearby elements.Through the mechanical property test,it is found that the yield strength of 7050 aluminum alloy after cryogenic treatment is about 35 Mpa higher than that of 479 Mpa without cryogenic treatment,and the tensile strength is about 38 Mpa higher than 538 Mpa at peak age of 120°C;After cryogenic treatment,the yield strength of 7050 aluminum alloy is about 12 Mpa higher than that of 560 Mpa without cryogenic treatment,and the tensile strength is about 10 Mpa higher than 596Mpa;and the strength of T74 7050 aluminum alloy did not increase significantly.The TEM was used to observe the precipitation phase of the 7050 aluminum alloy and the DSC curve analysis.It was found that the cryogenic treatment had a pre-aging effect.The T6 state 7050 aluminum alloy with enhanced strength after cryogenic treatment had more precipitated phases.It was found by electrochemical tests that the cryogenic treatment had no significant effect on the polarization behavior of 7050 aluminum alloy.However,it was found by electrochemical impedance test that the electrochemical impedance of 7050 aluminum alloy after cryogenic treatment was significantly improved,it shows that the corrosion resistance of 7050 aluminum alloy can be effectively improved by cryogenic treatment.Immersion test of 7050 aluminum alloy was using intergranular corrosion solution formulation by intergranular corrosion test standard,analysis of the development of intergranular corrosion of 7050 aluminum alloy in T6 and T74 after different periods ofsoaking.The surface corrosion morphology was observed by scanning electron microscopy(SEM)after clearing surface corrosion products.The section of the sample was observed,and the degree of intergranular corrosion was evaluated by the depth of corrosion in the section.It is found that the cryogenic treatment has little effect on the initial morphology of intergranular corrosion of 7050 aluminum alloy by short-time immersion.The surface morphology and cross-section morphology of the sample were observed after immersed 0~12h in intergranular corrosion solution,and the following results were obtained: in the T6 and T74 states,the number of pitting pits on the surface of the 7050 aluminum alloy that has been cryogenically treated is less than that of the non-cryogenic treatment,and the expansion rate is relatively slow;In the cross section,the depth of intergranular corrosion of the 7050 aluminum alloy subjected to cryogenic treatment is shallow relative to 7050 aluminum alloy without cryogenic treatment.Therefore,the cryogenic treatment technology has improved the intergranular corrosion resistance of 7050 aluminum alloy.