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设计一种新型Al-Cu-Li-Mg-Ag合金,研究热处理制度对新合金拉伸性能及裂纹扩展性能的影响,利用光学显微镜、透射电镜和扫描电镜等手段研究合金微观组织及断口形貌。结果表明:该新型铝锂合金经过540℃固溶1 h,(12%+RT/120 h+145℃/20 h)双级时效热处理后获得良好的综合性能:抗拉强度σ_b=443 MPa,屈服强度σ_(0.2)=397 MPa,延伸率δ=16.5%,裂纹扩展速率da/dn≈1.34×10~(-3) mm/cycle(△K=30 MPa·m~(1/2))。双级时效态下析出大量细小均匀的T_1相,在保证合金强度的同时,提高合金的抗疲劳裂纹扩展性能。T_8态下析出相对粗大的T_1相,θ′相和极少量的S′相,合金强度达到项目要求,抗疲劳裂纹扩展性能较差。T_3态下析出相数量少,合金强度不满足项目指标。
A new type of Al-Cu-Li-Mg-Ag alloy was designed to study the effect of heat treatment on the tensile properties and crack propagation properties of the new alloys. The microstructure and fracture morphology of the alloy were studied by optical microscope, transmission electron microscope and scanning electron microscope . The results show that the new Al-Li alloy has good comprehensive properties after two-stage aging treatment at 540 ℃ for 1 h and (12% + RT / 120 h + 145 ℃ / 20 h): tensile strength σ_b = 443 MPa, The yield strength σ_ (0.2) = 397 MPa, the elongation δ = 16.5% and the crack propagation rate da / dn≈1.34 × 10 -3 mm / cycle (△ K = 30 MPa · m 1/2) . A large number of small and even T_1 phases are precipitated under the two-stage aging, which improves the fatigue crack growth resistance of the alloy while ensuring the strength of the alloy. T_8 state precipitates relatively coarse T_1 phase, θ ’phase and a very small amount of S’ phase, the alloy strength to meet the project requirements, poor fatigue crack growth resistance. In the T_3 state, the amount of precipitated phase is small and the strength of the alloy does not satisfy the project index.