Tests under constant loading in a 0.6 M chloride medium carried out for a 7046 aluminium alloy in the T4 state showed hydrogen trapping at the grain boundaries leading to intergranular (IG) fracture. Assuming that hydrogen trapping at the hardening precipitates could be beneficial for the in-service behaviour, the efficiency of these precipitates as hydrogen trapping sites was studied using scanning Kelvin probe force microscopy (SKPFM). T4 samples were aged at 150 °C for 5, 20 and 48 hours allowing hardening precipitate growth. Apparent hydrogen diffusion coefficients decreasing from 2.10-10 cm².s-1 for the T4 state to 5.10-11 cm².s-1 for the overaged state were measured by using SKPFM for samples after hydrogen charging in sulfuric acid. This was attributed to hydrogen trapping at the hardening precipitates slowing down its diffusion. Analyses of the fracture surfaces of the samples revealed that the extent of the brittle hydrogen-affected surface decreased when the duration time of the ageing treatment increased with a transition from IG fracture mode to quasi-cleavage. The effect of pre-strain on apparent hydrogen diffusion coefficients was also studied to focus on the hydrogen / dislocations interactions. Finally, the results allowed to identify an optimized microstructure to enhance hydrogen embrittlement resistance and highlighted the specific role of hydrogen trapping on hardening precipitates.