The Study Of The Microstructure And Mechanical Properties Of Hollow Ingots Of 7A04 Aluminum Alloy

The 7A04 aluminum alloy hollow-ingot(outer diameter of 380 mm, inner diameter of 60 mm) was manufactured by a continuous casting route. The main test methods included metallographic microscope, vicker hardness tester, scanning electron microscopy and the mechanical tester. The samples were cut from the hollow ingot of as-cast, homogenous annealing and hot rolling states respectively, the microstructure and mechanical properties of the samples in different positions and the changes in the different layers were studied.Experimental results show some differences in the microstructure and mechanical properties between horizontal and vertical directions of the continuous casting large cross-section of hollow ingot. The grains and mechanical properties in the inner and outer layers are finer than that in the middle layer. After homogeniously annealed at 460 ℃ and helded for 24 h, a large number of reticular T-phase(Al2Mg3Zn3) in the grain boundaries are fully dissolved into the matrix, and a large number of acicular and spherical phases were precipitated in the matrix. The homogenous annealing can help reduce the differences and improve the comprehensive mechanical properties of hollow ingot casting. The experiments also suggest that the properties of 7A04 aluminum alloy can be effectively improved by proper rolling process and heat treatment. The experiments prove that after a T6 treatment, the tensile strength of the outermost layers can be reached to 550 MPa and enhanced by nearly 1.4 times when compared with that(231MPa) in homogenizing annealing state.