Effect Of Aging Treatment On Microstructure And Mechanical Properties Heterogeneity Of A 2519A Aluminum Alloy Thick Plate

2519A aluminum alloy has a wide range of applications in aerospace,weaponry and transportation due to its advantages of low density,high strength,good ductility and good stress corrosion resistance.However,the practice has proved that the 2519A aluminum alloy thick plate for armor is prone to crack in the thickness direction during service,which seriously reduces the service life.In response to this problem,this paper starts with the analysis of the microstructure and mechanical property of the thick plate,effects of aging treatment on the microstructure and mechanical properties of 2519A aluminum alloy thick plate were studied by means of metallographic observation,scanning electron microscope observation,transmission electron microscope observation,hardness test,room temperature tensile and fatigue performance test.The conculsions are listed as follows:(1)There is obvious heterogeneity of microstructure and mechanical properties of the2519A-T87 aluminum alloy plate along the thickness direction.The grains and the second phase of the RD-ND and TD-ND planes are heterogeneously distributed according to the microstructure observation.The grain size of the middle layer and the area fraction of the coarse second phase particles are both higher than that in the surface layer and the surface layer.The volume fraction of the precipitates is higher than that of the middle layer.The coexistence ofθ’and theθprecipitates is observed at the surface layer,and the single type ofθ’precipitates is observed in the middle layer.In terms of mechanical properties,the strength of the alloy in the rolling direction decreases,and the elongation increases from the surface layer to the middle layer.The increase in the elongation of the middle layer is mainly caused by the increase in uniform strain.According to the fracture surface observation,the fractures in the surface layer are dominated by tough dimples,and there are a small number of holes caused by the coarse undissolved phase.From the surface layer to the middle layer,the pore size continues to increase,and the intergranular cracks increase,and the proportion of intergranular fractures increases.(2)The mechanical properties of the 2519A-T87 aluminum alloy thick plate in the thickness direction are significantly lower than the rolling direction.From the point of view of tensile properties,the tensile strength of the thick specimen reduced 20 MPa even compared with that of the middle layer specimen along the rolling direction,with the lowest one in strength,and the elongation after fracture is sharply reduced to 1.5%,The main fracture mode of the thick specimen is transgranular cleavage fracture.According to the fatigue properties,the fatigue life of the thick specimen under high loading stress is significantly lower than that of the rolling specimen.The difference between the fatigue life of the thick specimen and the rolling specimen decreases as the loading stress decreases.When the loading stress is 190MPa,the fatigue life of the two samples is almost equivalent,and they reach 10~7 cycles.(3)After T9I6 treatment,the hetereogenity of the microstructure in the thickness direction is reduced,and the mechanical properties in the thickness direction are significantly improved.From the surface layer to the middle layer,the variation tendency of the T9I6 alloy in grain sizes,coarse second phases and precipitates is equal to the T87 treated alloy.However,compared with the T87 state,the precipitated phase is more fine and diffuse.From the mechanical property point of view,the yield strength,tensile strength and elongation of the T9I6 specimen in the thickness direction are increased by 12.9%,21.7%and 26%compared to the T87 state,respectively.The fracture modes of T9I6 are mixed intergranular and transgranular fracture.The fatigue life of the T9I6 specimen is also significantly higher than that of the T87 sample.