NaCl溶液中恒载荷作用对7020铝合金板材显微组织和拉伸性能的影响 Effect of Constant Load in NaCl Solution on Microstructure and Tensile Properties of 7020 Aluminum Alloy Sheet

通过室温拉伸测试、光学显微镜、扫描电镜和透射电镜等方法研究了3.5%NaCl溶液中恒载荷)应力值200, 250, 300 MPa)作用对7020铝合金板材显微组织和拉伸性能的影响。结果表明：NaCl溶液中恒载荷作用后，板材的拉伸性能下降。随着加载应力值增加，板材的抗拉强度和伸长率不断下降，而屈服强度先下降后略有所上升。恒载荷作用后，板材表面出现了腐蚀坑和沿晶腐蚀缺陷，腐蚀深度随加载应力增加呈上升趋势；拉伸时这些缺陷处易产生应力集中，增加了裂纹源数量，降低了拉伸性能。300 MPa加载时稍增加板材中的位错密度，减小了NaCl溶液中恒载荷作用后屈服强度的下降程度。 The effect of constant load (200, 250, 300 MPa) in 3.5% NaCl solution on microstructure and tensile properties of 7020 aluminum alloy sheet was investigated by ambient temperature tensile test, optical microscopy, scanning electron microscopy and transmission electron microscopy. It is shown that tensile properties of the sheets decrease after constant load in NaCl solution. With the increase of load, ultimate strength and elongation tend to decrease, while proof yield strength decreases first and then increases slightly. After constant load in NaCl solution, there are a number of corrosion pits and intergranular faults; the corrosion depth tends to increase with the increase of load. During tensile test, stress concentration occurs at these sites, and therefore the number of crack sources is increased; consequently tensile properties are decreased. A load stress of 300 MPa increases slightly dislocation density in the sheet and therefore decreases the decrement of yield strength after constant load in NaCl solution.