The Effects of Test Temperature, Temper, and Alloyed Copper on the Hydrogen-Controlled Crack Growth Rate of an Al-Zn-Mg-(Cu) Alloy

Technical Report · Sun Sep 17 04:00:00 EDT 2000

DOI:https://doi.org/10.2172/821950· OSTI ID:821950

Young, Jr, G A; Scully, J R

The hydrogen embrittlement controlled stage II 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 and 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 (from underaged to overaged) produced slower stage II crack growth rates. The stage II crack growth rate of each alloy 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 fracture path was predominantly 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 effect of copper additions on stage II crack growth rate in humid air. In the 2.19 wt.% copper alloy, the significant decrease ({approx} 10 times at 25 C) in stage II crack growth rate upon overaging is attributed to an increase in the apparent activation energy for crack growth. IN the 0.06 wt.% copper alloy, overaging did not increase the activation energy for crack growth but did lower the pre-exponential factor, {nu}{sub 0}, resulting in a modest ({approx} 2.5 times at 25 C) decrease in crack growth rate. These results indicate that alloyed copper and thermal aging affect the kinetic factors that govern stage II crack growth rate. Overaged, copper bearing alloys are not intrinsically immune to hydrogen environment assisted cracking but are more resistant due to an increased apparent activation energy for stage II crack growth.

• Research Organization: Lockheed Martin Corporation, Schenectady, NY 12301 (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC12-00SN39357
• OSTI ID: 821950
• Report Number(s): LM-00K082
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
36 MATERIALS SCIENCE
42 ENGINEERING
ACTIVATION ENERGY
AGING
AIR
ALLOYS
BEARINGS
COPPER
COPPER ADDITIONS
COPPER ALLOYS
CRACK PROPAGATION
FRACTURES
HUMIDITY
HYDROGEN
HYDROGEN EMBRITTLEMENT
KINETICS
TEMPERATURE DEPENDENCE