The identification of hydrogen trapping states in an Al-Li-Cu-Zr alloy using thermal desorption spectroscopy

Thermal desorption spectroscopy (TDS) was utilized to identify several metallurgical states in an Al-2Li - 2Cu-0.1Zr (wt pet) alloy, which trap absorbed hydrogen. Six distinct metallurgical desorption states for hydrogen were observed for tempers:varying from the T3 to peakaged condition. Lower energy thermal desorption states were correlated: with interstitial sites, lithium in solid solution, and delta' (Al3Li) precipitates. These states have trap-binding energies less than or equal to 25.2 kJ/mol. Under the charging conditions utilized, approximately 4 pet of the:total (e.g., trapped and lattice) hydrogen content was associated with interstitial sites, consistent with the view that the intrinsic lattice solubility of hydrogen in aluminum is very low. in contrast, dislocations, gain boundaries, and T-1 (Al2CuLi) particles were found to be higher energy-trap states with trap-binding energies greater than or equal to 31.7 kJ/mol. Approximately 78 pet of all absorbed hydrogen occupied these states.; Moreover, greater than 13 pet of the available trap sites at grain boundaries were occupied. Such: a high hydrogen coverage at grain-boundary sites supports the notion that hydrogen contributes to grain-boundary environmental cracking in Al-Li-Cu-Zr alloys. Also, it points out the error in assuming that hydrogen cannot play a major role in cracking of Al-based alloys due to the low lattice solubility.