## 1 Introduction  
In the era of development of environmentally friendly energy or automotive industry, in which the increase of the share of hydrogen as fuel is planned, it is important to recognize the influence of this gas on the properties of construction materials such as aluminum alloys. The influence of hydrogen on metals was observed more than half a century ago (1960s) [1]. Hydrogen absorption in metals causes their \"hydrogen embtitlement\" [2; 3; 4], as well as changes in their electrochemical properties [5; 6; 7]. Hydrogen embtitlement causes a reduction in mechanical properties, while a change in electrochemical properties causes a reduction in the corrosive properties of metal alloys [5]. Lowering both types of properties result in shortening the operational reliability time [8; 9], which may affect both the safety of users and the shorter service life of metal alloy constructions [10; 11; 12]. The knowledge of the influence of hydrogen on structural alloys may allow us to increase the safety of use, but also to extend the service life of devices, which in turn contributes to environmental protection, as it postpones the need to manufacture new parts [13]. For this reason, research on the influence of hydrogen on various types of metal alloys is very important. The most widely used construction materials are still metal alloys [14; 15; 16; 17]. Due to the appropriate mechanical parameters and relatively low-price, steels are mainly used [18; 19]. However, aluminum alloys, which are increasingly used in the aviation, space industry, automotive [19; 20; 21], shipbuilding and many other industries [22; 23], including space industries [24], also occupy a permanent place. Aluminum alloys are used not only as a material for the body structure of a vehicle, but also as a material for suspensions, inlet manifolds, gearbox housings, engine blocks, cylinders heads, but also pneumatic and liquid lines [25]. Some aluminum structural elements may be exposed to hydrogen ingress [26; 27; 28]. Such a situation occurs in the case of aluminum hydrogen pipes, aluminum hydrogen powered combustion engines or fuel cells (where the structural parts are made of aluminum alloys) [29; 30]. In fact, in most of these cases, the hydrogenation of aluminum alloys occurs in contact with gaseous hydrogen (often under pressure). However, in the first place, the authors wanted to continue research on the influence of hydrogen on the previously studied types of alloys. Earlier studies included measurements of the effect of hydrogen on corrosive properties of aluminum alloys [7] during electrolytic hydrogenation, and therefore the next step is to perform measurements on the mechanical strength of the same type of alloys during the same type of hydrogenation. Generally, aluminum alloys are corrosion resistant materials. However, the highly corrosion-resistant aluminum alloys do not have high resistance to the stress corrosion crack (SCC) propagation and may deteriorate under operating conditions due to fracture and corrosion fatigue [31]. Hydrogen is stored in the spaces inside the metal in molecular form (H\({}_{2}\)), which increases the pressure of hydrogen in the volume of the metal. This pressure causes internal stresses and blisters, which significantly reduces the mechanical resistance of the metal [32]. Moreover, the real metal crystal lattice is characterized by many crystallographic defects [33]. Due to the defects of the crystal lattice and the uneven stress distribution, the absorbed hydrogen is also unevenly distributed [32; 33]. Unevenly absorbed hydrogen causes distortions of the crystal lattice, which in turn affects the formation of local internal stresses. Such uneven distribution of the absorbed hydrogen also causes uneven distribution where tensile stresses occur, which consequently lowers the mechanical properties of metal alloys. Thus, such a situation also adversely affects the properties of structures made of aluminum alloys.