Stress corrosion cracking of superplastically formed 7475 aluminum alloy

Tsai, Tsong-Chang; Chang, Joshua; Chuang, Tung‐Han

doi:10.1007/s11661-997-0168-5

Cited by 10 publications

(9 citation statements)

References 26 publications

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“…The addition of Sc and Zr to high strength Al-Zn-Mg alloys have been found to simultaneously improve the tensile strength and SCC resistance, comparing with the conventional Al-Zn-Mg-(Cu) base alloys. 26,27) …”

Section: Electrochemical Behaviormentioning

confidence: 99%

“…15,17) On the other hand, the larger grain boundary precipitates can trap more atomic hydrogen to nucleate hydrogen bubbles, thereby decreasing the hydrogen concentration at grain boundary below a critical value to prevent intergranular SCC fracture. 26,27) Furthermore, the cathodic grain boundary precipitates grow by depleting solute atoms, broadening the anodic PFZ which contained no strengthen precipitation phase, was soft and weak.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Microstructure on the Mechanical Properties and Stress Corrosion Cracking of an Al-Zn-Mg-Sc-Zr Alloy by Various Temper Treatments

Wang

Hsu

et al. 2007

Mater. Trans.

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The high strength Al-Zn-Mg alloy used in the aerospace industry is strengthened by coherent G.P. zones and semicoherent 0 phase. However, this series of aluminum alloys are susceptible to stress corrosion cracking (SCC), particularly when aged to the peak-aged state of T6 temper. In this study, the effect of microstructure on mechanical properties and stress corrosion cracking of the alloy was investigated for alloys tempered to T6, RRA, Two-Step and T7 conditions by tensile test in air, SCC test and polarization test in a 3.5%NaCl solution. It is shown that the improvement in SCC resistance correlates very well with the size of matrix precipitates and grain boundary precipitates. T7 temper can produce larger sizes of both the matrix precipitates and grain boundary precipitates than that of T6, RRA and Two-step tempers, causing a decrease in the length and density of dislocation lines, which results in the decrease of stress concentration at grain boundary and greatly improving the SCC resistance. The addition of Sc and Zr to high strength Al-Zn-Mg alloys has been found to simultaneously improve the tensile strength and SCC resistance.

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Section: Electrochemical Behaviormentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Microstructure on the Mechanical Properties and Stress Corrosion Cracking of an Al-Zn-Mg-Sc-Zr Alloy by Various Temper Treatments

Wang

Hsu

et al. 2007

Mater. Trans.

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“…Yield strength, toughness and stress-corrosion cracking (SCC) resistance are the three major properties of heat-treatable high strength 7xxx aluminium alloys (Al-Zn-Mg based), when used in upper wing aircraft structures [1,2,3,4,5]. Whilst the SCC resistance is relatively difficult to be quantitatively assessed, the electrical conductivity, however, can be used as a measure of the SCC resistance.…”

Section: Aims and Scopementioning

confidence: 99%

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Starink

2003

Metall Mater Trans A

113

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A physically-based model for the electrical conductivity of peak aged and overaged Al-Zn-Mg-Cu (7xxx series) alloys is presented. The model includes calculations of the η and the S phase solvus (using a regular solution model), taking account of the capillary effect and η coarsening. It takes account of the conductivity of grains (incorporating dissolved alloying elements, undissolved particles and precipitates) and solute depleted areas at the grain boundaries. Data from optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) along with energy dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM) are consistent with the model and its predictions. The model has been successfully used to fit and predict the conductivity data of a set of 7xxx alloys including both Zr containing alloys and Cr containing alloys under various ageing conditions, achieving an accuracy of about 1% in predicting unseen conductivity data from this set of alloys.

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“…It is well documented that AA7xxx in the over-aged temper exhibits better stress corrosion cracking (SCC) resistance than in the peak aged condition [18][19][20][21][22][23][24]. Most SCC testing is done in a solution environment, and it was just shown that humidity has little effect on the sharp IGC fissure kinetics.…”

Section: Temper Effectsmentioning

confidence: 99%

“…It is interesting that the hardness of the as-received AA-7178 was similar to the T6 sample, but the current density during pretreatment was lower than that measured on both the T6 and T7 samples. It has been reported that corrosion resistance is improved in the over-aged condition [18][19][20][21][22][23][24]. Given these conflicting data, the exact temper of the as-received samples is still in question.…”

Section: Temper Effectsmentioning

confidence: 99%

Kinetics of sharp intergranular corrosion fissures in AA7178

Huang

Frankel

2007

Corrosion Science

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During service in structural aircraft applications, AA7178 has been found to develop sharp intergranular corrosion (IGC) fissures, a special form of attack. A new laboratory approach to quantify the kinetics of sharp IGC fissure growth was developed in this work. Sharp IGC fissures, similar to those formed in service, grew in samples that were given an electrochemical pre-treatment and then exposed in a humid environment. The time for the first sharp IGC fissure to penetrate the thin sample was determined by visual observation of the back side of the sample. The depth of the sharp IGC fissure was determined by serial sectioning. The kinetics measured by this approach did not represent the fastest rates, but rather the rates of long sharp IGC fissures. Relative humidity had no measurable effect on fissure kinetics, indicating that there was little connection of the local sharp IGC fissure region with the outside environment. AA7178 in the as-received and T7 conditions exhibited slower sharp IGC fissure rates than in the T6 condition. The sharp IGC fissures were found to be filled with corrosion products, which possibly exert a stress that could play an important role in driving fissure growth. It is suggested that the sharp IGC fissure could be a form of SCC.

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Stress corrosion cracking of superplastically formed 7475 aluminum alloy

Cited by 10 publications

References 26 publications

Effects of Microstructure on the Mechanical Properties and Stress Corrosion Cracking of an Al-Zn-Mg-Sc-Zr Alloy by Various Temper Treatments

Effects of Microstructure on the Mechanical Properties and Stress Corrosion Cracking of an Al-Zn-Mg-Sc-Zr Alloy by Various Temper Treatments

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Kinetics of sharp intergranular corrosion fissures in AA7178

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