双级时效对含Sc的Al-Zn-Mg-Zr合金组织与性能的影响

Effect of two-step ageing treatment on microstructure and properties of Al-Zn-Mg-Zr alloy containing Sc

通过慢应变速率拉伸实验(SSR_T)、晶间腐蚀试验、剥落腐蚀实验、室温力学性能测试、电导率测试、维氏硬度测量和透射电子显微分析等手段对2.5 mm厚Al-5.4Zn-2.0Mg-0.25Sc-0.1Zr合金板材在双级时效下的抗应力腐蚀性能(SCC)、抗晶间腐蚀性能(IGC)、抗剥落腐蚀性能(EC)、力学性能、电学性能、显微组织结构及其演变规律进行研究。研究结果表明:合金较适宜的双级时效工艺为120℃/6 h+140℃/20 h,在此工艺条件下合金的抗拉强度R_m、屈服强度R_p、伸长率A和电导率γ分别为553 MPa,534 MPa,12.0%和22.3 MS/m,双级时效后合金晶内为弥散分布的亚稳定强化相η′-MgZn_2,晶界出现粗大不连续分布的平衡相η-MgZn_2,还伴有明显宽化的无沉淀析出带。与单级峰值时效(120℃/24 h)相比,合金晶间腐蚀倾向减小,具有良好的抗剥落腐蚀性能,剥蚀等级为中等剥落腐蚀(EB)级,具有良好的抗应力腐蚀性能。

The stress corrosion cracking resistance, intergranular corrosion resistance, exfoliation corrosion resistance, mechanical properties, electrical conductivity and microstructure of A1-Zn-Mg-Zr alloy containing Sc after two-step ageing treatment were investigated by means of slow strain rate tention（SSRT）, intergranular corrosion, EC experiments, room temperature tensile test, hardness and electric conductivity measurement, and transmission electron microscopy. The results show that the ultimate tensile strength, yield strength, elongation and electrical conductivity of the alloy are 553 MPa, 534 MPa, 12.0% and 22.3 MS/m, respectively after duplex aging （120℃ /6 h＋140 ℃/20 h）. After the two-step ageing treatment, crystal dispersed within the metastable strengthening phases η＇-MgZn2, and grain boundaries are not continuous equilibrium phases η-MgZn2, accompanied by a certain width PFZ, which reduces the tendency of intergranular corrosion and contributes to an evident improvement in the exfoliation corrosion resistant and stress corrosion cracking resistant, compared with single step aging treatment. The level of exfoliation corrosion is moderate exfoliation corrosion （EB）.