Al–Zn–Mg–Cu alloys in T6 temper are susceptible to hydrogen embrittlement via intergranular cracking. This study investigates the effects of laser surface heating and re-aging on the hydrogen embrittlement sensitivity of 7075 aluminum alloy using slow strain rate tensile tests in humid air (HA) and dry nitrogen gas (DNG). Scanning a laser over the surface of a T6-tempered specimen reduced its hardness, while subsequent re-aging restored it to the level of the original T6 temper. Scanning transmission electron microscopy observations adjacent to grain boundaries revealed that the width of precipitate free zone and the size and number density of grain interior precipitates were similar regardless of treatment. However, grain boundary precipitates were coarser in the laser-treated and re-aged specimen. The elongation of the T6-tempered specimen was lower in HA than in DNG, owing to hydrogen-induced intergranular cracking. Meanwhile the laser-treated and re-aged specimen exhibited comparable strength and elongation to those of T6-tempered specimen in DNG and enhanced resistance to hydrogen embrittlement in HA. These results suggested that laser surface heating and re-aging treatment suppressed hydrogen embrittlement by promoting coarsening of grain boundary precipitates in the near-surface region.
Manaka et al. (Thu,) studied this question.