Effect of the Microstructures Adjacent to the Grain Boundaries on the Mechanical Properties and Hydrogen Embrittlement Susceptibilities of Al-Cu Alloys.

To investigate the effect of the microstructure adjacent to the grain boundaries on the mechanical properties and hydrogen embrittlement susceptibilities in the Al-Cu base 2219 alloy, alloy specimens were solution-treated and then aged at 100°C, 130°C, and the usual aging temperature of 190°C, to control the alloy microstructure in the vicinity of grain boundaries. The slow strain rate technique was conducted on the specimens in humid air and dry nitrogen gas environments to evaluate the effect of environmental hydrogen on them. Transmission electron microscopy was used to measure the grain boundary precipitate size and precipitate-free zone width of the specimens. Thermal desorption analysis was conducted on the gauge sections of the fractured specimens to evaluate the trapping sites and amount of hydrogen desorbed. The specimens aged below 190°C had finer grain boundary precipitates than those aged at 190°C. The test environment did not affect the specimen strength under any of the aging conditions 100°C, 130°C, and 190°C. Some samples had intergranular fractures on their entire fracture surfaces, irrespective of the test environment. The thermal desorption analysis results showed no significant difference between the hydrogen emission spectrum and the amount of hydrogen released within each temperature range. Thus, hydrogen embrittlement does not occur in the 2219 alloy, irrespective of the characteristics of its microstructure adjacent to the grain boundaries. [ABSTRACT FROM AUTHOR]