The results of positron lifetime and Doppler broadening spectrum of defects in the hydrogen charged non-heat treatable 5xxx Al alloys were presented here. The yield stress of the sample was reduced for about 20MPa after hydrogen was charged. A similar trend was observed in positron lifetime measurement, as the average lifetime tav descended remarkably to almost the level of Al matrix. The change in coincidence Doppler broadening spectroscopy was also significant, exhibited by the characteristic change in coincidence Doppler broadening radio curves of a sample before and after hydrogen was charged. After hydrogen charging, there was an obvious enhancement in the high momentum region compensating disenhancement in the low momentum region. This indicated the existence of hydrogen filling effect. The vacancies around the Mg atoms should be preferential filling sites for hydrogen because Mg has a strong affinity for hydrogen. The formation of an Mg–H bond parallel to a grain boundary was an important factor in weakening the grain boundary cohesion.

Positron Lifetime and Doppler Broadening Study of Defects in Hydrogen Charged Al–Mg Alloys. X.Wang, Y.Zhong, B.Wang, H.Zhang:  Journal of Materials Research, 2009, 24[5], 1791-4