Effect of ageing on the Al-Zn-Mg aluminium alloys properties

Aluminium alloys are nowadays used in a lot of industries. Indeed, they are light, they have good mechanical properties and can be easily be formed. They are besides weldable for some of them and can be compatible with hydrogen. That is why a lot of studies have been carried out to determine their capacity to be able to be used for hydrogen storage tanks, alone or combined with composite materials. Here is presented the studies results obtained after ageing of hydrogen tanks carried out from an Al-Mg-Zn alloy. The starting material is in the state T652, obtained by forging after the foundry and then a treatment of dissolution, following by a deformation of a few percent before being submitted to a staged heat treatment. Pieces are then carried out by machining. They are then welded by electrons beam and are then submitted to a new heat treatment of dissolution followed by a staged thermal treatment which led them to the T6 state. The results described here will concern the initial characterizations of the pieces, and the characterizations after different period of ageing times. Hydraulic failure tests are presented. These results are compared to hardness and metallurgical parameters characterizations in order to draw conclusions on the evolution of the material. (O.M.)