【作者】 吴蓉；

【导师】 张瑞丰；

【作者基本信息】 中南大学 ， 材料学， 2023， 硕士

【摘要】 铝锂合金在航空航天领域得到广泛应用,但容易发生腐蚀,Mg合金化和时效处理都会对合金中析出相的分布和种类产生影响。为了给铝锂合金成分和热处理制度优化提供参考,提高合金的耐腐蚀性而进行本研究。本文以不同Mg含量的铝锂合金为研究对象,采用晶间腐蚀、剥落腐蚀、电化学测试、应力腐蚀等性能检测方法,通过金相显微镜、透射电镜、扫描电镜、背散射电子衍射、差示扫描量热等微观组织表征手段,研究了Mg合金化和时效制度对铝锂合金腐蚀行为和微观组织的影响,得到以下结论:（1）合金中Mg含量对时效析出行为有重要影响,适量Mg的加入（0.7Mg）使T₁相的析出明显加速,而过量Mg（1.1Mg）的加入抑制其析出。铝锂合金腐蚀模式的转变是由Mg含量的变化导致的晶内和晶界析出相的变化引起的。首先,连续的晶界析出相和较少的晶内析出相导致了晶间腐蚀。其次,连续的晶界析出相和较多的晶内析出相导致坑蚀（以晶粒腐蚀为特征）产生。最后,晶界中不连续的析出相和晶粒中较多的析出相产生轻微的点蚀。三种Mg含量合金随着时效时间延长表现出相似的腐蚀模式转变:时效早期为局部晶间腐蚀,长时间时效发生点蚀。（2）时效处理制度对铝锂合金的析出行为也有影响,T8态Al-Cu-Li-0.4Mg合金相比T6态拥有更多位错等优先形核位点,有利于T₁相在晶粒内部均匀形成,抑制了晶界无析出带的形成,合金的抗腐蚀能力得到提高。（3）加载方向对Al-Cu-Li-0.4Mg合金应力腐蚀裂纹扩展有显著影响,RD样品的裂纹扩展速率高于TD样品,归因于晶界对裂纹扩展的阻碍效应和施密特因子高低对裂纹扩展难易程度的影响。同时,T8样品的裂纹扩展速率明显低于T6样品,归因于T8态样品中析出相更均匀细小,且不存在无析出带,阻碍了裂纹的扩展。施加电位控制后的Al-Cu-Li-0.4Mg合金应力腐蚀敏感性增加。图65幅,表8个,参考文献119篇更多还原

【Abstract】 Aluminum-lithium alloys are widely used in the aerospace field,but they are prone to corrosion.Both Mg alloying and aging treatments affect the distribution and types of precipitated phases in the alloys.Therefore,in order to provide a reference for the optimization of the composition and heat treatment of aluminum-lithium alloys,and to maintain corrosion resistance,the effect of Mg alloying and aging process on the corrosion behavior and microstructure of aluminum-lithium alloys was investigated by using experimental methods such as intergranular corrosion,exfoliation corrosion,electrochemical testing,stress corrosion,and microstructure characterization by means of metallographic microscopy,transmission electron microscopy,scanning electron microscopy,backscattered electron diffraction,and differential scanning calorimetry,and the conclusions are as follows:（1）The variation of Mg content in the alloy has an important effect on the aging precipitation phase,and the addition of moderate amount of Mg（0.7 Mg）accelerates the precipitation of T₁ phase,while the addition of excessive amount of Mg（1.1 Mg）inhibits the precipitation process.The transformation in the corrosion mode of Al-Li alloy caused by the Mg content is caused by the change of grain boundary and precipitation phases in grain boundary.First,the continuous precipitation phase in grain boundary and the less intracrystalline precipitation phase led to intergranular corrosion.Second,continuous precipitation phase in grain boundary and more intracrystalline precipitation phase led to pit corrosion characterized by grain corrosion.Finally,discontinuous precipitation phases in the grain boundaries and more precipitation phases in the grains produce shallow pitting.As the aging time increases,the corrosion patterns of the three Mg content alloys show a similar pattern:localized intergranular corrosion at the early aging stage,and pitting corrosion occurs with prolonged aging.（2）The aging treatment also has an effect on the precipitation behavior of the Al-Li alloy.The pre-deformed T8 state Al-Cu-Li-0.4Mg alloy has more preferential nucleation sites such as dislocations compared with the T6 state,which is conducive to the uniform formation of the T₁ phase inside the grain and inhibits the formation of precipitation-free zones at grain boundaries,and the corrosion resistance of the alloy is improved.（3）The loading direction has a significant effect on the stress corrosion crack extension of Al-Cu-Li-0.4Mg alloy,and the crack extension rate of RD samples is higher than that of TD samples,which is attributed to the hindering effect of grain boundaries on crack extension and the influence of the high and low Schmidt factor on the ease of crack extension.Meanwhile,the crack extension rate of T8 sample is significantly lower than that of T6 sample,which is attributed to the fact that the precipitation phase is more uniform and smaller in the T8 sample,and there is no precipitation-free zone,which brings obstruction to the crack extension.The stress corrosion susceptibility of the Al-Cu-Li-0.4Mg alloy increased after the application of potential control.更多还原