The effects of test temperature, temper, and alloyed copper on the hydrogen-controlled crack growth rate of an Al-Zn-Mg-(Cu) alloy

Abstract

The hydrogen embrittlement controlled stage I1 crack growth rate of AA 7050 (6.09 wt.% Zn, 2.14 wt.% Mg, 2.19 wt.% Cu) was investigated as a function of temper arid alloyed copper level in a humid air environment at various temperatures. Three tempers representing the underaged, peak aged, and overaged conditions were tested in 90% relative humidity (RH) air at temperatures between 25 and 90 "C. At all test temperatures, an increased degree of aging @om underaged to overaged) produced slower stage II crack growth rates. The stage n crack growth rate of each alIoy and temper displayed Arrhenius-type temperature dependence with activation energies between 58 and 99 kJ/mol. For both the normal copper and low copper alloys, the fiacture path was predominately intergranular at all test temperatures (25-90 "C) in each temper investigated.Comparison of the stage II crack growth rates for normal (2.19 wt.%) and low (0.06 wt.%) copper alloys in the peak aged and overaged tempers showed the beneficial effixt of copper additions on stage II crack growth rate in humid air. In the 2.19 wt.% copper alloy, the significant decrease (-10 times at 25 "C) in stage I1 crack growth rate upon overaging is attributed to an increase in the apparent activation energy for crack growth. Ir: the 0.06 wt.% copper alloy, overaging did not increase the activation energy for crack growth but did lower the pre-exponential factor, vo, resulting in a modest (-2.5 times at 25 "C) decrease in crack growth rate. These resuits indicate that alloyed copper and thermal aging affect the kinetic factors that govern stage II crack growth rate. Overaged, copper bearing alloys are not intrinsicaIly immune to hydrogen environment assisted cracking but are more resistant due to an increased apparent activation energy for stage IT crack growth. BACKGROUND

Spatial determination of diffusible hydrogen concentrations proximate to pits in a Fe–Cr–Ni–Mo steel using the Scanning Kelvin Probe

“…Tritium autoradiography, nuclear reaction analysis, scanning electrochemical microscopy, microprinting, and rescaled pits using thermal desorption spectroscopy (TDS) were applied for spatial H detection. [9][10][11][12][13][14][15][16][17] Permeation was employed for temporal resolution of H during atmospheric exposure. [18] The Scanning Kelvin Probe (SKP), SKP force microscope (SKPFM), and SKP combined with TDS and secondary ion mass spectrometry are promising new methods for spatial H detection with lateral and depth profiling (utilizing cross-sections of samples).…”

Nanostructured thin films for hydrogen-permeation barrier

“…The presence of hydrogen in many metallic materials, such as carbon steel, [1][2][3][4][5] stainless steel, [6][7][8][9] and aluminum alloys, [10][11][12] is widely known to negatively affect the mechanical characteristics. In particular, steel composed primarily of ferrite or martensite structures with higher strength is known to have high hydrogen diffusibility and strong tendency to suffer from hydrogen embrittlement.…”

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