Intergranular corrosion of high-purity aluminum in hydrochloric acid. I -, Effects of heat treatment, iron content, and acid composition / M. Metzger and J. Intrater.
The intergranular corrosion of high-purity aluminum in hydrochloric acid was studied as a function of iron content, heat treatment, and acid composition under conditions where the rate of intergranular penetration was of the order of 1 millimeter per week. The behavior of specimens quenched to retai...
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| Format: | Government Document Book |
| Language: | English |
| Published: |
Washington, D.C. :
National Advisory Committee for Aeronautics,
1954.
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| Series: | Technical note (United States. National Advisory Committee for Aeronautics) ;
3281. |
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| Summary: | The intergranular corrosion of high-purity aluminum in hydrochloric acid was studied as a function of iron content, heat treatment, and acid composition under conditions where the rate of intergranular penetration was of the order of 1 millimeter per week. The behavior of specimens quenched to retain a single-phase structure indicated the rate of attack on the high-angle grain boundaries to be influenced by the segregation in these boundaries of iron and possibly other impurity atoms. Under the conditions studied, this segregation reduces the rate of attack; this led to the conclusion that the boundaries are inherently anodic. When the heat treatment was such that precipitation of a second phase could have occurred, the corrosion behavior could not be correlated with the small amount of second phase actually observed on microscopic examination, and it was postulated that pre-precipitation concentration gradients iin the metal can have a strong influence on corrosion. Intergranular attack is rapid when there is a continual evolution of hydrogen gas from the intergranular crevice. Rapid attack can be obtained at low acid strengths by increasing the copper or iron content of the acid. This favors the strong attack on the low-angle grain and subgrain boundaries observed after certain heat treatments. Metallic impurities in the acid can also be responsible for preferential corrosion of the grain bodies observed in portions of some specimens with relatively inactive boundaries. When both the strength and the metallic-impurity content of the acid are low, a protective film forms over the surface and intergranular attack is very slow. |
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| Item Description: | "February 1955" NACA TN Number 3281. |
| Physical Description: | 38 pages : illustrations ; 27 cm. |
| Bibliography: | Includes bibliographic references. |