Mechanism Of Heat Treatment Regulating Microstructures And Properties Of 7B05 Alloy Profiles

7B05 alloy profiles have been widely applied in bearing components of high-speed trains in China.However,there is still a gap between the synergistic effect of strength,toughness and corrosion resistance for the industrial alloy profiles and similar materials in the world.Combined with the research tasks of the National Key Research and Development Program of China,the mechanism of the homogenization of ingot,solid solution/quenching and aging heat treatment on the microstructure and properties of 7B05 alloy profiles during the preparation process are investigated in the dissertation.The principle of regulating microstructure and properties of this alloy profiles by heat treatment is expounded,and the prototype of innovative homogenization and aging treatment is proposed.The noble conclusions are as follows:（1）Combined with phase diagram calculation and experiments,the dissolution/precipitation behavior of the second phases during the homogenization process for the industrial 7B05 alloy ingots are studied.The results show that the Mg Zn₂ phases gradually dissolve in the temperature range of 350℃～420℃,which provides the heteronucleation location for Al₃Zr phases at the Mg Zn₂/matrix interface,and promotes the precipitation of Al₃Zr particles near Zr poor grain boundaries.（2）The three-stage homogenization prototype is established with the Mg Zn₂ dissolution/precipitation temperatures,the Al₃Zr phases initial temperatures and the non-equilibrium eutectic dissolution temperature as the reference values.Compared with single-stage homogenization,the ratios of high angle grain boundary decrease from 43.1%to 26.5%,and the ratios of recrystallized structure decrease from 44.7%to 25.3%in the7B05 alloy profiles.Intergranular corrosion（IGC）depth of peak-aged7B05 alloy profiles decreased from 85μm to 53μm,and the exfoliation corrosion（EXCO）grade increases from ED to EC.（3）The effect of off-line solid solution/quenching and on-line quenching on deformation substructures,residual crystalline phases and subsequent aging precipitation behavior of 7B05 alloy profiles is revealed:Deformation substructures retained in on-line quenching of the studied profiles can compensate for the off-line solid solution/quenching to improve the contribution of quenching supersaturated solid solution to strength,and inhibit the broadening of PFZs,which is beneficial to the synergistic improvement of strength and toughness.（4）The regulation mechanism of natural aging and natural aging-artificial aging on microstructure and properties of on-line quenching 7B05 alloy profiles are expounded.The coordination of strength,toughness and corrosion resistance of the PFZs for 7B05 alloy profiles is revealed:Under experimental conditions,the toughness and corrosion resistance of 7B05 alloy profiles is increasing with PFZs width in 80～140nm,while the width of PFZs is more than 139nm both have a downward trend.Increasing the width of PFZs,the decreasing trend of corrosion resistance is weaker than toughness.If the width of PFZs continues to increase,the downward trend of corrosion resistance will be weaker than that of toughness.（5）For 7B05 alloy profiles,multi-stage aging heat treatment technology prototype is established,which combines low temperature（90°C）and secondary high temperature（150°C）after high temperature（185°C）regression treatments.The size and density of intragranular and grain boundary precipitations are controlled,the width of PFZs is reduced,and the comprehensive properties of profiles are improved.Under this condition,tensile strength,yield strength,elongation,impact toughness for the 7B05 aluminum alloy profiles are 373MPa,324MPa,16.4%,41J/cm²,respectively.IGC grade is 2,EXCO grade is PB.E_corr,R_p,I_SSRTunder EXCO conditions for the 7B05 alloy profiles are-873.3m V,1199Ω/cm²,7.0%,respectively.