## 1 Introduction  
Hybrid structures are increasing in the automotive, aerospace, and naval industries, especially when these vehicles are electric or hybrid, making energy efficiency crucial for cost savings. When it is necessary to join components of different materials, adhesive bonding is the primary method employed [1]. It ensures good mechanical strength, mitigates stress concentrations, and offers better corrosion resistance properties [2]. When these materials are metallic alloys, they need to undergo surface treatments to enhance their corrosion resistance and increase their surface area, developing mechanical anchorage sites. In the case of aluminum alloys, the primary treatment used is anodization, which creates a thin alumina (Al\({}_{2}\)O\({}_{3}\)) oxide layer on the order of micrometers. This improvescorrosion resistance in environments rich in Cl\({}^{-}\) ions and provides a certain degree of affinity with some adhesives [2; 3]. The anodization process has several disadvantages, such as the use of extremely acidic electrolytes, high sensitivity to the chemical composition and surface condition of the substrate, and significant environmental and health risks [4]. Should the by-products from the anodizing procedure be indiscriminately released into the sewage infrastructure, it has the potential to instigate eutrophication, a phenomenon that ought to be meticulously circumvented. It is imperative to implement post-treatment protocols for the resultant effluents to avert this issue, which consequently incurs supplementary expenditures associated with transportation and treatment, and amplifies bureaucratic processes due to regulatory compliance [5; 6; 7]. To mitigate the environmental repercussions associated with the acidic anodization process, an electrochemical methodology predicated on anodization but utilizing elevated voltage levels (ranging from 100 to 700 V) was conceived in the 1970s. This advancement facilitated the implementation of more ecologically sustainable solutions, including those derived from silicates, aluminates, and borates, among various others. Referred to as Plasma Electrolytic Oxidation (PEO) or Micro-Arc Oxidation (MAO), this methodology is esteemed for its advantageous properties, which encompass elevated productivity, the utilization of benign and environmentally responsible alkaline electrolytes, enhanced hardness attributed to localized temperature surges that may attain levels of up to 25,000 K, and improved corrosion resistance resultant from the formation of a compact layer adjacent to the substrate. Furthermore, it affords an exceptional adhesion of the coating to the substrate [2; 8]. Although PEO is a highly innovative and effective process, it consumes a significant amount of energy. To initiate the ionization process of gasses, present in the microbubbles near the substrate, voltages start at 100 V-120 V and reach final potentials around 400 V-450 V. This makes the process economically unfeasible for some companies compared to conventional methods with cheaper post-treatment [9; 10; 11; 12; 13; 14]. In the literature, studies focus on optimizing the physical and chemical characteristics of oxide coatings. [PERSON] et al. [15] investigated the time optimization of the PEO process to stabilize corrosion in aluminum alloys. [PERSON] et al. [16] optimized the PEO process on CP Grade 1 titanium sheets to improve photocatalytic properties. However, it is observed that there are few studies in the literature that aim to optimize surface properties using electrolytic plasma in light alloys, such as aluminum for applications in hybrid structures. Recognizing the need to optimize adhesion between dissimilar materials, this study employs a Central Composite Design (CCD) factorial design to optimize three PEO process parameters: immersion time (X1), duty cycle (X2), and the electrolyte concentration of sodium tetraborate Na\({}_{2}\)B\({}_{4}\)O\({}_{7}\)\(\cdot\)10H\({}_{2}\)O (X3).