## 1 Introduction  
In assembly technology, established joining technologies are screwing, riveting, welding or soldering. Adhesive bonding is replacing these more and more due to its many advantages, such as the possibility of joining hybrid joints, a reduction in weight and cost, and an even distribution of stress within the materials to be joined [1; 2]. Furthermore, an adhesive bonding process is adaptable and tolerance compensating. Complex geometries can be bonded without great effort, and both small surfaces and large components can be securely joined with a well-designed process. The adhesive layer can also have additional functional properties. For example, it can have a vibration-damping, corrosion-inhibiting or electrically or thermally conductive or insulating effect [3; 4; 5]. The challenge with bonded joints is that bonding is a complex process that depends on many parameters and have to be designed optimally for each process. In addition to choosing an adhesive suitable for the substrate, parameters such as the adhesive gap, the contact pressure, the surrounding atmosphere and, above all, suitable pretreatment of the substrate surfaces are decisive for the strength of a bond [3; 6; 7; 8; 9; 10]. For industrial applications, aluminum is a widely used material that is frequently bonded. Areas of application include the automotive or aerospace industries, where high demands are placed on the bonded joint [11; 12; 13; 14]. After the manufacturing process, the aluminum surface is covered by a complex layer, which consists of impurities such as residual lubricants and residues from the manufacturing process [11]. Since this layer forms a weak boundary layer that reduces the cohesive strength of the bond, the surface must be cleaned before bonding. Due to the high oxygen affinity of aluminum, an oxide layer (Al\({}_{2}\)O\({}_{3}\)) about 1-2 nm thick forms in the air within a few nanoseconds, on the surface of which hydrated oxides and hydroxides are present, which act as bonding partners for the adhesive [15]. In practice, the surface of the aluminum is pretreated for successful bonding. A variety of pretreatment methods is used for this purpose [10; 16; 17; 18]. Mostof them are complex multi-stage processes. The most common method is a sequence of mechanical abrasion, vapor degreasing and alkaline cleaning. However, since the adhesion and durability of bonded joints with mechanically treated and alkaline cleaned substrates are not optimal, and the structure and properties of the aluminum oxide layer are critical to the effects on adhesion, a targeted build-up of a synthetic aluminum oxide layer is critical to the quality of the bonded joint [17]. The most common chemical treatments for building a suitable aluminum oxide layer are based on chromium-sulfuric acid etching, in which the substrate is immersed in a solution of sulfuric acid and potassium dichromate [19]. Since these are costly, time-consuming and environmentally harmful processes, the question of a possible alternative arises [20]. The approach investigated in this work refers to the complete bonding of aluminum substrates without an intervening oxide layer and without the use of environmentally harmful chemicals [21]. The effect of different oxide layer thicknesses has been previously considered both in theory and in practice [16; 22], but what causes complete removal of the oxide layer has not been investigated due to the large effort required to create an oxygen-free atmosphere. In this study, an oxygen-free atmosphere is created by the rather new method of doping an inert gas atmosphere with silane. Deoxidation, in this case by mechanical grinding, in a technically oxygen-free environment, prevents the reformation of the oxide layer and allows the bonding of pure aluminum. Thus, if the bond between the substrate and the adhesive layer is successful, the strength-limiting factor of a native aluminum oxide layer is quickly and easily eliminated.