2099铝锂合金晶间腐蚀行为与时效制度的相关性

Correlation Between Intergranular Corrosion Behavior and Aging Treatment of 2099 Al-Li Alloy

系统研究了2099铝锂合金晶间腐蚀行为与时效制度(T6态150和175℃时效、T8态150℃时效)的相关性,建立了2099铝锂合金腐蚀-时效进程状态图。结果表明,时效过程按腐蚀类型变化可以分为4个阶段。时效早期发生孔蚀或局部晶间腐蚀,欠时效阶段发生全面晶间腐蚀,近峰时效阶段转变为局部晶间腐蚀,过时效阶段以孔蚀为主。欠时效时,细小的晶界析出相连续分布,晶间腐蚀敏感性较高。过时效阶段晶界析出相粗化,并呈不连续分布,抗晶间腐蚀能力提高。时效温度提高,晶界析出相粗化,析出相间距增加,而时效前预变形能够促进析出相均匀弥散形核,抑制晶界无沉淀带形成,因而导致晶间腐蚀欠时效阶段和近峰失效阶段的时效时间范围缩短或消失,提高了抗晶间腐蚀能力。

The correlation between the intergranular corrosion （IGC） behavior and the aging temper （including T6 aging at 150 and 175 ℃, T8 aging at 150 ℃） of 2099 Al-Li alloy was investigated. Then a diagram was established to describe the relation of IGC with the aging procedure. According to the aging resulted corrosion morphology of the alloy, the aging process might be divided into four stages： i.e. stage Ⅰ is the initial aging stage, stage Ⅱ the under-aging stage, stage Ⅲ the near-optimal aging stage and stage Ⅳ the over-aging stage. The aged alloy showed different modes corrosion after aged by different stages： i.e. pitting corrosion or local intergranular corrosion （LIGC） for stage Ⅰ; general intergranular corrosion （GIGC） for stage Ⅱ; LIGC for stage Ⅲ; and pitting corrosion without IGC for stage Ⅳ. In the under-aged alloy, a great number of very fine precipitates preferentially deposited along grain boundaries, which seem like a continuous chain, hence resulting in the highest susceptibility to IGC for the alloy. In the over-aged alloy, the precipitates were coarsened and the inter-precipitate spacing became larger, so that the susceptibility to IGC may be suppressed. In general, with the rising of aging temperature, the grain boundary precipitates grew coarse and the spacing between the precipitates became larger, while a proper pre-deformation of the alloy might facilitate the uniform nucleation of precipitates and suppress the formation of precipitate-free zone （PFZ） along grain boundary. These two factors shortened or even eliminated the Stage Ⅱ and Stage Ⅲ, therewith increasing the resistance to IGC of the alloy.