回归温度对7055铝合金挤压棒材力学性能和抗腐蚀性能的影响

Effect of retrogression temperature on mechanical properties and corrosion resistance of 7055 aluminum alloy extruded bars

通过导电率、力学性能测试、局部腐蚀性能测试和慢应变速率拉伸应力腐蚀性能测试,结合金相显微镜(OM)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等微观组织表征方法,研究了回归温度对7055铝合金挤压棒材力学性能和抗腐蚀性能的影响。结果表明:当回归温度为180℃时,可获得与T73处理相当的抗应力腐蚀性能,合金抗拉强度和屈服强度显著提升,分别由T73处理的579.5 MPa和540.7 MPa提高至692.5 MPa和674.6 MPa,应力腐蚀敏感指数(I_(SSRT))为2.5%。当回归温度提高至200℃时,可获得与T73处理相当的力学性能和抗应力腐蚀性能,合金抗晶间腐蚀和剥落腐蚀性能有了较大改善,最大腐蚀深度分别减小到24.8μm和36.2μm。回归温度由180℃提高至200℃、220℃,晶界析出相(GBPs)的尺寸从10.5 nm增大至24.6 nm、39.6 nm,基体沉淀相(MPs)的尺寸从7.9 nm增大至13.5 nm、18.6 nm,Cu含量分别从2.1%升高至3.2%和3.4%(摩尔分数),无沉淀析出带(PFZs)的宽度分别从33.4 nm增大至60.7 nm和108.2 nm。确定了力学性能与腐蚀性能协同的回归温度,探明了合金力学性能以及抗腐蚀性能变化主要是由晶界析出相和基体沉淀相尺寸以及无沉淀析出带宽度的增大以及GBPs成分偏析而导致的机理。

The effects of retrogression temperature on the mechanical properties and corrosion resistance of 7055 aluminum alloy extruded bars were investigated by the electrical conductivity,mechanical properties,localized corrosion tests and tensile stress corrosion tests at slow strain rate,combined with microstructure characterization methods including optical microscope(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that,when the retrogression temperature is at 180℃,the stress corrosion cracks resistance of the alloys is comparable to that of the T73 treatment.The tensile strength and yield strength of the alloys are significantly increased from 579.5 MPa and 540.7 MPa to 692.5 MPa and 674.6 MPa,respectively.The slow strain rate tensile tests index(ISSRT)is 2.5%.When the retrogression temperature increases to 200℃,the mechanical properties and stress corrosion cracks resistance of the alloys are comparable to those of T73 treatment.The intergranular corrosion resistance and exfoliation corrosion resistance of the alloys are greatly improved,and the maximum corrosion depths reduce to 24.8μm and 36.2μm,respectively.The retrogression temperatures increase from 180℃to 200℃and 220℃,the sizes of grain boundary precipitates(GBPs)and matrix precipitates(MPs)increase from 10.5 nm to 24.6 nm and 39.6 nm,7.9 nm to 13.5 nm and 18.6 nm,respectively,Cu content increases from 2.1%to 3.2%and 3.4%,the widths of precipitate free zones(PFZs)increase from 33.4 nm to 60.7 nm and 108.2 nm.The regression temperature of mechanical properties and corrosion properties is determined,and the mechanism of the changes of mechanical properties and corrosion properties of the alloy are mainly caused by the increases of GBPs,MPs size and PFZs width,as well as the segregation of GBPs components.