晶粒组织对7020-T5铝合金型材强度和抗腐蚀性能的影响

Effect of grain structures on strength and corrosion resistance of 7020-T5 aluminum alloy profiles

通过室温拉伸试验、剥落腐蚀试验、慢应变速率拉伸试验和四点弯曲试验,并结合金相观察、电子背散射衍射(EBSD)和透射电镜(TEM)等微观组织分析技术,研究晶粒组织对7020-T5铝合金型材的强度、抗剥落腐蚀性能以及抗应力腐蚀性能的影响。研究结果表明:完全再结晶型材的室温拉伸强度较低,其抗剥落腐蚀性能达到N级,但型材的抗应力腐蚀性能严重恶化,应力腐蚀敏感指数I_(SSRT)为9.55%,四点弯曲试验中应力腐蚀裂纹沿着再结晶晶粒向内快速扩展,24 h即发生应力腐蚀断裂。表层粗晶和内部再结晶晶粒降低材料的力学性能,使应力腐蚀裂纹在型材表面深度方向上的扩展速率加快。晶粒细小、不含表层粗晶、再结晶分数低的均匀变形组织有利于获得更高的综合性能,具有该种晶粒组织的7020-T5铝合金型材的抗拉强度和屈服强度分别达到366.6 MPa和314.2 MPa,断后伸长率达到15.7%,抗剥落腐蚀性能达到PB级,应力腐蚀敏感指数I_(SSRT)为2.38%,四点弯曲应力腐蚀试验中表面产生腐蚀裂纹和发生应力腐蚀断裂的时间分别为580 h和1736 h,抗应力腐蚀性能优异。

The effect of grain structures on the strength and corrosion resistance 7020-T5 alloy profiles was studied through tensile test,exfoliation corrosion test(EXCO),slow strain rate tensile test(SSRT)and four-point bending test,combined with microstructure analysis such as optical microscope(OM),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The results show that the tensile strength of the fully recrystallized profile is remarkably low,and the EXCO resistance reaches N grade,but its stress corrosion resistance is seriously deteriorated,the stress corrosion cracking sensitivity index I_(SSRT)is 9.55%,and the stress corrosion crack propagates rapidly along the recrystallized grains in the four-point bending test,and fracture occurs within 24 h.Coarse grain layers on the surface and internal recrystallized grains decrease the mechanical properties,and accelerate the propagation rate of stress corrosion cracks in the depth direction.Uniform deformed microstructures with small grains,and no surface coarse grain layers and low recrystallization fraction favor to obtain higher comprehensive properties.The tensile strength and yield strength of 7020-T5 alloy profile with this grain structure reaches 366.6 MPa and 314.2 MPa,respectively,the elongation after fracture reaches 15.7%,the EXCO resistance reaches PB level,the I_(SSRT)is 2.38%,the time of the corrosion crack appeared on surface and fractured by stress corrosion cracking(SCC)in the four-point bending stress corrosion test are 580 h and 1736 h,respectively,showing excellent stress corrosion resistance.