Study On Microstructure,properties And Intergranular Corrosion Characteristics Of 7075 Aluminium Alloy Under Multi-Directional Forging And Aging

7xxx series aluminium alloys has high specific strength,ductility,toughness,and good processability,which make it widely used in the fields of rail transportation,military equipment,aerospace,etc.However,it is difficult to keep the strength,ductility and corrosion resistance of 7xxx series aluminium alloys simultaneously by conventional process at a high level.Therefore,it is necessary to improve the corrosion resistance via optimizing the internal microstructure by means of plastic working and heat treatment,without decreasing the strength and elongation.This paper takes the 7075 aluminium alloy as the research object,and processed by means of solid solution and aging treatment,multi-directional forging（MAF）and aging treatment.The mechanical properties and intergranular corrosion resistance of the materials were tested,and the microstructures were observed by means of metallographic microscopy,scanning electron microscopy,transmission electron microscopy,X-ray diffraction,etc.Finally,the effect of the microstructure on its mechanical properties and corrosion resistance was discussed.The main research results are as follows:（1）MAF results in a high density of dislocations(7.4×10¹⁴/m²),which greatly accelerates the nucleation and growth of precipitated phases.Thus,the G.P.zone almost transform into precipitated phases and dispersion evenly distributed in the matrix during subsequent aging,leading to more precipitated phases in the MAF and aging alloy compared to the solid solution and aging treated alloy.（2）Without compromising the ductility much,the comprehensive mechanical properties of the MAF and aging alloy are significantly improved.Its strength increased by 16.1%to about 606 MPa,the ductility decreased by only 2.9%to about16.6%,and the product of strength and elongation was about10.08 GPa%.The strengthening mechanism is due to increasing dislocation density,grain refinement and precipitating.The improvement of ductility is due to reducing residual stress and dispersing precipitates within fine grains.（3）The mechanical properties and corrosion resistance of7075 aluminium alloy are enhanced after MAF and aging,and the improvement of corrosion resistance is due to the coarse and discontinuously distributed grain boundary precipitates,which effectively prevents the spread of pitting corrosion along grain boundaries.The maximum corrosion depth is 21μm,and the corrosion grade is improved by two-stage compared to the solid solution and aging alloy（maximum corrosion depth is 150μm）.