Research On Stress Corrosion Cracking Property Evaluation And Corrosion Resistance Mechanism By Calculation Assistant For 7N01 Aluminum Alloy

This study focuses on the stress corrosion cracking(SCC)problem of 7N01 high-strength aluminum alloy.The convolutional neural network,first-principles calculation and finite element modeling are combined with experimental measurements such as microstructure observation,electrochemical testing,mechanical properties measurements and thermal simulation to establish the internal correlation model between the microstructure,mechanical behavior and corrosion resistance performance of 7N01 aluminum alloy profiles.Further,the effect of the recrystallized layer on the SCC of 7N01 aluminum alloy in the Clsolution with different concentrations is studied.The influence of element migration on the micro-galvanic effect at the compound/Al matrix interface is quantitatively calculated.The extrusion process parameters to improve the corrosion resistance of 7N01 aluminum alloy are explored.The aim of this paper is to provide theoretical basis and data support for the safety service of 7N01 highstrength aluminum alloy profiles.The main results of this study are as follows:(1)The differences in mechanical behavior and corrosion resistance of different parts on the surface of large-size 7N01 aluminum alloy profiles are identified.4800 sets of "metallographic image-hardness(HV)-corrosion potential(Ecorr)" data sets are collected through experiments and a convolutional neural network model for predicting substrate hardness and corrosion potential through microstructure images is established.The prediction accuracy of the model for hardness and corrosion potential on 3840 datasets reaches 91%and 87%,respectively,and on 960 testing sets,the prediction accuracy reaches 90%and 82%.On the new dataset,the mean average errors between the predicted values and the experimental values of hardness and corrosion potential is 1.8 HV and 7.0 mV,thus,the model has great generalization ability.(2)The quantity,distribution and evolution of precipitates at grain boundaries along the thickness direction of 7N01 aluminum alloy profile are analyzed.The diffusion of Cu in the recrystallization zone results in transformation of MgZn2 phase into MgZn(Cu)phase.DFT calculation shows that the work function differences of MgZn2 phase/Al matrix and MgZn(Cu)phase/Al matrix on(100)plane are 0.151 eV and 0.073 eV,respectively.The CI is easier to adsorb on MgZn2(111)plane.The experimental results show that the discontinuous distribution of MgZn(Cu)phase(about 60 nm)at the grain boundary reduces the SCC susceptibility.(3)The micro electrochemical mechanism of SCC initiation of 7N01 aluminum alloy is studied.The average Volta potential difference between αAlFeMnSi phase and A1 matrix decrease from 648.370 mV to 432.383 mV,when the content of A1 increase by 1.44%and the content of Fe and Si decrease by 0.97%and 0.30%,respectively.The calculation results show that the average work function difference between α-AlFeMnSi phase and A1 matrix decreased from 0.232 eV to 0.065 eV with the reduction of Fe,Mn and Si elements content of αAlFeMnSi phase.When the temperature is higher than 550℃,the Mn element inα-AlFeMnSi phase diffuses into the matrix,which weaken the micro-galvanic corrosion effect of α-AlFeMnSi phase/Al matrix,and reduce the SCC susceptibility.(4)The plastic deformation constitutive model and dynamic recrystallization model of 7N01 aluminum alloy are established,and the extrusion simulation of the profile is carried out with Deform-3D software.The suitable extrusion conditions for recrystallized layer formation on the surface of the profile are proposed:the billet temperature is 500℃-525℃,and the extrusion speed is 7 mm/s-10 mm/s.Subsequent verification experiments show that recrystallization occurs on the surface of the 7N01 aluminum alloy extrusion under the suitable extrusion parameters,which is consistent with the simulation results and the corrosion resistance of the sample is improved after extrusion.