| The service environment of aircraft alloy material is very complicated, especially in coastal areas, due to the humid air, and a great deal of corrosive industrial gas emissions, aircraft components will be subjected to various forms of corrosions, in which exfoliation corrosion, intergranular corrosion and stress corrosion are very common. And many catastrophic accidents are caused by corrosion damage. Therefore, alloy materials for aircraft should not only have high strength, but also should have good fatigue performance and corrosion resistance. The effects of Zr on microstructure and properties of Al-Cu-Mg-Ag alloy were investigated by microstructure observation, hardness test, tensile test at room temperature, fatigue performance test and corrosion resistance test through optical microscope, scanning electron microscope, hardness tester and universal material testing machine. The following conclusions are obtained:(1) With the increase of Zr, the grain size of the alloy becomes smaller and smaller, and the grain boundary gradually becomes finer. The smallest size of the grain is the alloy which contained 0.3wt.%Zr, its grain size is about 50μm, reduced by 40μm compared with the alloy which contained no zirconium, but the grain size is uneven when compared with the alloy that contained 0.2wt.%Zr. But the addition of Zr has little influence on the second phase composition, the suitable homogenizing heat treatment is 500℃×24h, and the solution heat treatment is 515℃×2h.(2) The peak hardness is improved and the platform area in age hardening curves disappear after the addition of zirconium. But the hardness of the alloy reached its maximun value almost in the same time. The peak hardness of the alloy which contained 0.2wt.%Zr is 173.3MHV.(3) The room temperature strength is improved and the elongation remains above 10 percent after the addition of zirconium. The tensile strength and yield strength of the alloy that contained 0.2wt.%Zr were 503.4MPa and 475.6MPa, which is the highest, increased by 30MPa and 35.3MPa respectively compared with the alloy with no zirconium. But the strength of the alloy decreased when the addition of zirconium increased from 0.2% to 0.3%.(4) The fatigue resistance is improved after the addition of zirconium. The fatigue limit of the alloy which contained 0.2wt.%Zr is 191.0MPa, and the fatigue limit of the alloy which contained no zirconium is 191.0MPa. The fatigue fracture of the alloys is divided into the fracture source zone, crack propagation zone, and instantaneous fracture zone, in which the area of the crack propagation zone is the largest. The size of the instantaneous fracture zone of the alloy contained 0.2wt.%Zr is smaller than the alloy contained no zirconium under the same stress condition.(5) The corrosion resistance is improved after the addition of zirconium. With the increase of zirconium, the continuity of the alloy in the intergranular corrosion forms turns into the discontinuous corrosion and the maximum depth of intergranular corrosion become smaller and smaller. The maximum corrosion depth of the alloy contained 0.3wt.%Zr and 0.2wt.%Zr were 25.48μm and 30.41μm, decreased by 211.36μm and 206.43μm respectively compared with the alloy that contained no zirconium. The time to the exfoliation corrosion grade EA of the alloy contained 0.3wt.%Zr and 0.2wt.%Zr was 12 hours, lagged 6 hours compared with the alloy that contained no zirconium.(6) With the increase of Zr, the self-corrosion potential of the alloy becomes higher and higher, the self-corrosion current density becomes smaller and the capacitance arc radius become bigger, which comes to the same conclusion with the intergranular corrosion test and spalling corrosion test. The self-corrosion potential of the alloy contained 0.2wt.%Zr and 0.3% was about-0.61V, improved by 6.2 percent compared with the alloy contained no zirconium.(7) The comprehensive performance of the alloy was enhanced after the addition of zirconium, and the alloy contained 0.2wt.%Zr has the best comprehensive performance. |
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