非等温回归再时效对7050铝合金组织与力学性能的影响

Effect of Non-isothermal Retrogression and Re-ageing Treatments on the Microstructure and Mechanical Properties of 7050 Alloy

采用扫描电镜(SEM)、透射电镜(TEM)、硬度测试和拉伸测试研究了非等温回归再时效对7050合金组织和力学性能的影响。非等温回归处理的加热速率为5℃/min,回归终了温度包括160℃、190℃、220℃、260℃和300℃。结果表明:经120℃/24 h+RT 5℃/min 190℃+120℃/24 h的非等温回归再时效处理后,合金的力学性能最佳,其抗拉强度约为588 MPa,屈服强度约为558 MPa,延伸率约为23%,硬度值约为199HV。预时效态合金晶界平衡相η呈不连续分布,其尺寸约为49~70 nm,晶内析出相η′的平均尺寸约为5~6 nm;在190℃的非等温回归处理过程中,预时效态合金中的析出相发生了部分回溶,相的平均尺寸变小,其晶界相和晶内相的尺寸分别约为5~10 nm和3~6 nm,回归态合金晶界呈多列平行且无沉淀析出带(PFZ)不明显;再时效态合金的晶界相尺寸最大,约为91~108 nm,晶内相弥散,尺寸约为4~10 nm,无沉淀析出带变得明显,其宽度约为41 nm。

The effects of“non-isothermal retrogression and re-ageing”treatments on the microstructure and mechanical properties of a 7050 alloy were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),hardness test and tensile test.During the non-isothermal retrogression process with a heating rate of 5℃/min,five terminal temperatures of 160℃,190℃,220℃,260℃and 300℃were selected.The results show that after the non-isothermal retrogression and re-ageing treatment of 120℃/24 h+RT 5℃/min 190℃+120℃/24 h,the alloy presents the best mechanical properties with the ultimate tensile strength of 588 MPa,yield tensile strength of 558 MPa and ductility of 23%,respectively;the hardness is 199HV.In the pre-aged alloy,the equilbriumηphases along the grain boundaries are discontinuously located with an average size of 49—70 nm,and theη′phases in the grains have an average size of 5—6 nm.During the retrogression with the continuous temperature increasing to 190℃,the pre-precipitated phases are partly dissolved and the sizes are smaller:the grain boundaryηphases have an average size of 5—10 nm,and the phases within the grains have an average size of 3—6 nm.The retrogression alloy has multiple and parallel grain boundaries with unobvious PFZ.The re-aged alloy has the biggest phases in an average size of 91—108 nm along grain boundaries and diffuse phases inside grains in an average size of 4—10 nm,and its PFZ becomes clear with a width of 41 nm.