THE ROLE OF THE T1 PHASE IN THE PREEXPOSURE AND HYDROGEN EMBRITTLEMENT OF AL-LI-CU ALLOYS

A series of slow strain rate tests were conducted on longitudinal specimens of two Al-Li binary and two Al-Li-Cu alloys, to determine the possibility of embrittlement by hydrogen and to investigate the role of the T1 phase in the embrittlement process. The binary Al-Li alloys were not embrittled. The copper-containing alloys were susceptible to hydrogen embrittlement that can be induced by pre-exposing in NaCl solution or simultaneous cathodic charging and straining. It was shown that the T1 phase facilitates hydrogen entry into the copper-containing alloys and is responsible for their susceptibility. The hydrogen embrittlement susceptibility of the different microstructures of the two Al-Li-Cu alloys was found to correlate very well with the amount of T1 present and the slip behavior. The fracture mode was mainly transgranular. Some secondary intergranular cracking was also present and its extent related to the amount and distribution of hydrogen present.