Effects of retrogression and re-aging treatment on microstructure and properties of extruded thick plate of spray formed 7055 aluminum alloy

doi:10.13251/j.issn.0254-6051.2020.10.026

Abstract

Abstract: Effects of retrogression and re-aging(RRA) treatment on the microstructure and properties of extruded thick plate of spray formed 7055 aluminum alloy were studied by means of mechanical properties test, exfoliation corrosiontest and transmission electron microscopy (TEM) observation. The results show that although when adopting the retrogression temperature of thick plates as the plate loading temperature, the specimon heating process still needs to take a long time, and increasing the retrogression temperature is beneficial to shortening the staying time of specimens in the low temperature stage. After RRA treatment with pre-aging at 120 ℃ for 14 h, retrogression at 185 ℃ for 130 min and at 190 ℃ for 118 min, re-aging at 120 ℃ for 24 h, the longitudinal yield strengths of the specimens are 649.3 MPa and 652.6 MPa respectively, which are higher than 621.5 MPa of the T76 specimens, and the exfoliation corrosion resistance is close to that of the T76 specimen and reaches the EB level. After RRA treatment, the precipitated phase in the matrix is mainly η′ phase with a small amount of GP zone, the size of which is 3-10 nm, and the precipitates at grain boundary distribute intermittently. Increasing the heating rate of the thick plate specimen in the low temperature stage of retrogression process is beneficial to increasing the strength of the specimen after re-aging, and increasing the retrogression temperature seems to be beneficial to improving the exfoliation corrosion resistance of the RRA specimen.

Key words: 7055 aluminum alloy, thick plate, retrogression and re-aging (RAA), microstructure, mechanical properties, exfoliation corrosion

CLC Number:

TG146.2

Tang Zhihao, Ye Qingfeng, Zhou Jiandang, Fan Xi, Zhang Hao, Feng Di. Effects of retrogression and re-aging treatment on microstructure and properties of extruded thick plate of spray formed 7055 aluminum alloy[J]. Heat Treatment of Metals, 2020, 45(10): 129-134.

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