固溶处理温度对峰值时效7050铝合金晶间腐蚀敏感性的影响

Effect of solution-treating temperature on intergranular corrosion of peak-aged 7050 Al alloy

采用光学显微镜、X射线衍射、扫描电镜、透射电镜、浸泡试验等方法,研究固溶处理(465~490℃, 1 h)对峰值时效(120℃, 24 h)7050铝合金晶间腐蚀的影响规律。浸泡结果表明:随着固溶处理温度提高,峰值时效合金晶间腐蚀敏感性先逐渐降低后又升高,其中,经(485℃, 1 h)固溶处理的峰值时效合金的晶间腐蚀抗力显著提高。微观组织分析和晶界偏聚建模表明:适当提高固溶处理温度,不仅促进S-Al2CuMg2相溶解,还增大Cu在晶界偏聚浓度,从而提高峰值时效合金晶界η-Mg(Zn,Cu)2相中的Cu含量。据此初步提出:晶界η-Mg(Zn,Cu)2相中Cu含量的增加使其腐蚀电位正移,从而缩小了与无析出区的腐蚀电位差,使得二者形成微电偶的倾向性下降,由此造成峰值时效合金晶间腐蚀敏感性相应逐渐降低、甚至消除。至于更高温度固溶处理的峰值时效合金再次发生晶间腐蚀,这与合金发生过烧、形成S-Al2CuMg2相有关。

The effects of solution-treating temperatures(465-490 ℃, 1 h) on the intergranular corrosion of 7050 Al alloy peak-aged at 120 ℃ for 24 h were investigated by optical microscope, X ray diffraction, scanning electron microscope, transmission electron microscope and accelerated corrosion test. The immersion test indicates that the intergranular corrosion(IGC) susceptibility of the alloy decreases first, and then increases with the solution-treating temperatures increasing. Especially, the IGC resistance can be enhanced significantly for the peak-aged sample solution-treated at 485 ℃. Furthermore, the microstructural observations and grain boundary segregation modeling show that the increase of the solution-treating temperatures leads to the accelerated dissolution of S-Al2CuMg2 and increases Cu segregation at grain boundaries, and then increases the Cu content of the grain boundary η-Mg(Zn,Cu)2 precipitating in the peak-aged alloy. Based on the above results, it can be proposed preliminarily that the positive shift of the corrosion potential of the corrosion potential of the grain boundary η-Mg(Zn,Cu)2 precipitates due to the increased Cu content shortens the potential difference with the precipitation free zones, which will decrease the tendency to form the grain boundary microcouplings and then reduce, even remove the IGC susceptibility of the alloy. By comparison, the increased IGC susceptibility of the alloy solution-treated at higher temperatures is related to the S-Al2CuMg2 phase in the eutectics as a result of over-burning.