Effect of pre-annealing treatment on the microstructure and mechanical properties of extruded Al–Zn–Mg–Cu alloy bars

Abstract

Taking extruded Al–Zn–Mg–Cu alloy (7A04 alloy) bars as the research object, the effect and mechanism of pre-annealing treatments on the microstructure and mechanical properties of the aged alloy bars were investigated. The results show that a pre-annealing treatment at 350°C for 15 h before a T6 treatment substantially reduced the sensitivity of the microstructure and mechanical properties of the extruded 7A04 aluminum alloy specimens toward the extrusion temperature. The average grain sizes of the specimens extruded at 390 and 430°C after T6 treatment were 3.4 and 8.1 μm, respectively, and their elongations to failure were 7.0% and 9.2%, respectively. However, after pre-annealing + T6 treatment, the differences in both the grain sizes and the elongations of the specimens became small, i.e., their average grain sizes were 3.2 and 3.8 μm and their elongations were 12.0% and 13.3%, respectively. For the specimens extruded at the same temperature, pre-annealing treatment obviously improved the plasticity of the alloy, which is attributed to an increase in soft texture or to grain refinement in the specimens as a result of the pre-annealing + T6 treatment.

Keywords

aluminum alloy / hot extrusion / pre-annealing treatment / microstructure / mechanical properties

References

[1] Hou W.R., Zhang Z.H., Xie J.X., Ma Q.M., Gai H.T. Temperature inhomogeneity on cross section of Al alloy hollow profile based on reverse point tracking method. Chin. J. Nonferrous Met., 2015, 25(7): 1798.

[2] Sanabria V., Mueller S., Reimers W. Microstructure evolution of friction boundary layer during extrusion of AA 6060. Procedia Eng., 2014, 81, 586.

[3] Gu W., Li J.Y., Wang Y.D. Effect of grain size and taylor factor on the transverse mechanical properties of 7050 aluminium alloy extrusion profile after over-aging. Acta Metall. Sin., 2016, 52(1): 51.

[4] Kayser T., Klusemann B., Lambers H.G., Maier H.J., Svendsen B. Characterization of grain microstructure development in the aluminum alloy EN AW-6060 during extrusion. Mater. Sci. Eng. A, 2010, 527(24-25): 6568.

[5] Chen J., Liang Z., Dai S., Shao W., Zhang B. Effects of grain shape and texture on the through-thickness yield strength of AA7055 aluminum alloy plate. Rare Met. Mater. Eng., 2008, 37(11): 1966.

[6] Li J.Y., Xie J.X., Song Y., Yin S., Gu W. The Isothermal Extrusion System and Method for Aluminum Magnesium Alloy Based on the Fuzzy Closed-Loop Control of Temperature, 2013

[7] Xie J.X., Li J.Y., Chen Y.L., Liu B. Device and Control System for Realizing Temperature Gradient Distribution of Extrusion Billet, 2011

[8] Tan C., Xu X.J., Jiang W., Sun L.S., Zhang L.X., Fan Y.Z., Zhao J.J. Effect of pre-recovery treatment on microstructure and properties of ultra high strength aluminum alloy extrusion treated by solid solution-T652 treatment. Chin. J. Nonferrous Met., 2015, 25(11): 3019.

[9] Xu X.J., Zhang Y.K., Deng P.A., Wu Y., Zhang Z.Q., Lu Y.D. Effect of pre-recovery-annealing treatment on microstructure and properties of extruded 7085 aluminum alloy. Trans. Mater. Heat Treat., 2014, 35(8): 36.

[10] Zhang X.M., Huang Z.B., Liu S.D., Liu W.H., Zhang C., Du Y. Effects of two-stage solution on microstructures and mechanical properties of 7A55 aluminum alloy. Chin. J. Nonferrous Met., 2006, 16(9): 1527.

[11] Chen K.H., Chao H., Fang H.C., Xiao D.H., Chen S.Y. Effect of step-solution on microstructure and local corrosion properties of Al−Zn−Mg−Cu aluminum alloy. J. Cent. South Univ. Sci. Technol., 2010, 41(5): 1730.

[12] Xu X.F., Zhao Y.G., Wang X.D., Zhang Y.Y., Ning Y.H. Effect of rapid solid-solution induced by electropulsing on the microstructure and mechanical properties in 7075 Al alloy. Mater. Sci. Eng. A, 2016, 654(27): 278.

[13] Bunge H.J. Texture Analysis in Materials Science, 1982, London, Butterworths Press 88.

[14] Lücke K., Pospiech J., Virnich K.H., Jura J. On the problem of the reproduction of the true orientation distribu tion from pole figures. Acta Metall., 1981, 29(1): 167.

[15] Hu G.X., Cai X., Rong Y.H. Fundamentals of Materials Science, 2010, Shanghai, Shanghai Jiao Tong University Press 97.

[16] Ma K.K., Wen H.M., Hu T., Topping T.D., Isheim D., Seidman D.N., Lavernia E.J., Schoenung J.M. Mechanical behavior and strengthening mechanisms in ultrafine grain precipitation-strengthened aluminum alloy. Acta Mater., 2014, 62(5): 41.

[17] Starink M.J., Wang S.C. A model for the yield strength of overaged Al−Zn−Mg−Cu alloys. Acta Mater., 2003, 51(17): 5131.

[18] Hmmphrey F.J., Hatherly M. Recrystallization and Related Annealing Phenomena, 2nd Ed., 2004, London, Pergamon Press 86.

[19] Terlinde G., Luetjering G. Influence of grain size and age-hardening on dislocation pile-ups and tensile fracture for a Ti−Al alloy. Metall. Trans. A, 1982, 13(7): 1283.