回归再时效处理对喷射成形7055铝合金挤压厚板组织与性能的影响

采用力学性能测试、抗剥落腐蚀性能测试、透射电镜(TEM)观察等方法,研究了回归再时效(RRA)处理对喷射成形7055铝合金挤压厚板微观组织与性能的影响。结果表明:厚板采用到温装炉的方式进行回归加热时,试样升温过程仍较长,提高回归加热温度有利于缩短试样在低温阶段的停留时间。试样经120 ℃×14 h预时效+(185 ℃×130 min、190 ℃×118 min)回归+120 ℃×24 h再时效两种RRA工艺处理后纵向屈服强度分别为649.3 MPa和652.6 MPa,高于T76试样的621.5 MPa;而抗剥落腐蚀性能与T76试样接近,达到EB级。试样经RRA处理后基体沉淀析出相主要为η′相+少量GP区,其尺寸为3~10 nm,晶界析出的η相呈断续分布。提高厚板试样在回归低温阶段的加热速率有利于提高试样再时效后的强度,而提高试样回归温度有利于提高RRA试样的抗剥落腐蚀性能。

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

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.