Solid Solution And Aging Process And Properties Of 7B52 Laminated Aluminium Alloy

To cope with the needs of modern battlefield environment,tanks and other armoured vehicles are gradually developing in the direction of light weight,and at the same time,armour materials are required to have high elasticity,high strength and high toughness,aluminium alloy laminated composites have better ballistic resistance than a single homogeneous alloy at the same mass,so they are widely used as protective materials for special vehicles.The 7B52 laminated aluminium alloy studied in this project is a hot-rolled composite of 7A52 and 7A62 aluminium alloys,which has a detrimental effect on the mechanical properties of the material due to the presence of equilibrium or eutectic phases in the hot-rolled 7xxx series aluminium alloy.However,as the strength increases,the sensitivity of the alloy to stress corrosion also increases,so a reasonable ageing process is essential to improve the overall performance of the material.In this paper,the effects of single-stage solution,single-stage ageing,double-stage ageing and regression re-ageing processes on the mechanical properties and electrical conductivity of the material are compared,and the changes in the properties of 7B52 laminated aluminium alloy and its component layer alloys under different solution and ageing treatment regimes are investigated by means of metallographic observation(OM),scanning electron microscopy(SEM)and energy spectrum analysis(EDS).The results of the paper show that: the 7B52 laminated aluminium alloy and its component layers were subjected to different solid solution and ageing treatment regimes.The results of the paper show that:With the increase of the solid solution temperature and the extension of the holding time,the strength of the solid solution state and the aging state of the 7B52 laminated aluminum alloy and the hardness of the group element layer alloy show a trend of change of first increasing and then decreasing,and the elongation gradually decreases,which is because the increase of the solid solution temperature or the extension of the holding time can improve the supersaturation of the matrix,when the solid solution temperature reaches470? and the holding time is 90 min,the matrix is fully solid solution and The mechanical properties of the material is the best,but when the solid solution treatment temperature and time exceed the appropriate range will make the alloy organization of the grain coarsening,recrystallization fraction increases,resulting in the mechanical properties of the alloy reduced,so the choice of solid solution process:(470 ± 5 ?)×90min after water quenching.After solid solution treatment,the coarse insoluble phase present in the tissue is Fe/Mn insoluble phase,which may lead to the reduction of material plasticity and should control the content of Fe and Mn.During the single-stage aging process,the strength of 7B52 laminated aluminium alloy showed a trend of first increasing and then decreasing with the increase of temperature and the extension of holding time,and the elongation showed a monotonically decreasing trend.The yield strength,tensile strength and elongation of 7B52 laminated aluminium alloy were557.4MPa,600 MPa and 11.1% respectively under the peak ageing process of 120?×24h.The strength of the 7B52 laminated aluminium alloy and the hardness of the component layer alloy are strengthened,but the conductivity of the component layer alloy is lower,mainly because the grain boundary precipitation phase is arranged in a continuous manner,which is easy to form anode channels and the material has poor stress corrosion resistance.Under the two-stage ageing process system,the secondary ageing temperature has the greatest influence on strength,hardness and conductivity,and the secondary ageing time is the greatest factor affecting the elongation of the laminated aluminium alloy.For the 7B52 laminated aluminium alloy,the optimal dual aging process is 105?×4h + 160°C×7h.Under this process system,the tensile strength and elongation are 576.1 MPa and 8.3% respectively;the hardness of the 7A52 and 7A62 alloys are 141.2 HV and 196.2 HV respectively,and the conductivity is 34.13% IACS and 32.62% IACS respectively.Under this two-stage ageing regime,the grain boundary precipitation phases in the group layer alloys are larger in size and intermittently arranged,and this grain boundary precipitation phase morphology is conducive to the improvement of the alloy's stress corrosion resistance,so the conductivity of each group layer is significantly increased compared to the peak ageing.The regression and re-aging system with better overall performance of 7B52 laminated aluminium alloy was peak aging + 180°C×10 min regression treatment + peak aging.Under this process,the intracrystalline precipitation phases of the 7A52 and 7A62 alloys are mainly diffuse and small G.P.zones and phases,which have a significant strengthening effect on the alloys;the grain boundary precipitation phases are large and discontinuously distributed,which help to reduce the susceptibility of the alloys to stress corrosion.The tensile fracture of the 7A52 layer alloy after the T6(peak aging),double-stage aging and RRA(regression and re-aging)aging processes were all tough fossil type through crystal fracture,and the RRA process resulted in a larger diameter and depth of the tough fossil at the fracture,so the elongation was better.7A62 layer alloy under the three aging processes,the tensile fracture was a mixture of along-crystal fracture and through-crystal fracture.EDS analysis of the coarse second phase particles at the bottom revealed that these coarse phases are Fe/Mn phases,which are likely to cause stress concentration during deformation,so the addition of Fe and Mn should be controlled within a reasonable range.