Due to the need to develop methods that optimize the surface properties of lightweight alloys such as aluminum, titanium, and magnesium and align with contemporary requirements of the 21st century, such as enhanced environmental and sanitary efficiency, the plasma electrolytic oxidation (PEO) process stands out as a comprehensive solution. This process can develop oxide coatings on the mentioned alloys, which exhibit superior physical and chemical properties compared with conventional methods. Since 2010, research in this area has been conducted with real-world applications. Recent studies have adopted experimental design approaches to optimize parameters to reduce operational costs and make the technology more accessible. The present study conducted a comparative analysis between treatments performed by conventional methods and by plasma processes, highlighting the most promising results.

Review A Comprehensive Review of Additive Manufacturing Technologies for Composite Materials Gabriela Galib 1, Francisco J. G. Silva 1,2,*, André F. V. Pedroso 1,3, Raul D. S. G. Campilho 1,2, Rafael Lucas 1,4 and Rita Sales-Contini 1,5 1 CIDEM, ISEP, Polytechnic of Porto, Rua Dr. António Bernardino de Almeida, 4249-015 Porto, Portugal 2 LAETA-INEGI, Associate Laboratory for Energy, Transports and Aerospace, Rua Dr. Roberto Frias 400, 4200-465 Porto, Portugal 3 Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Rua Dr Roberto Frias, 400, 4200-465 Porto, Portugal 4 School of Engineering and Sciences, São Paulo State University, Guaratinguetá 12516-410, São Paulo, Brazil 5 Aeronautical Structures Laboratory, Technological College of São José dos Campos Prof. Jessen Vidal (FATEC), São José dos Campos 12247-014, São Paulo, Brazil * Correspondence: fgs@isep.ipp.pt; Tel.: +351-22-83-40-500 Received: 15 October 2024; Revised: 6 February 2025; Accepted: 10 March 2025; Published: 17 March 2025 Additive manufacturing (AM) is a term used to describe technologies that utilize 3D model data to create physical objects by depositing materials in the form of powder, wire and/or resin. One of the applications of AM is in manufacturing composites, where two or more materials are combined to form a helpful engineering material. This review article covers the most common AM technologies used in composite manufacturing, including Laminated Object Manufacturing (LOM), Fused Deposition Modelling (FDM), Stereolithography (SLA), Selective Laser Sintering (SLS), and Direct Energy Deposition (DED). The work intends to provide a structured set of information for beginners or practitioners, helping to acquire the essential knowledge in this field in just a document, and this represents its main novelty, as no other articles have been found to provide a deep but synthetic set of information about this subject. The article describes each process’s main characteristics, advantages, and disadvantages and provides a brief SWOT analysis, offering examples of their use. In summary, AM of composite materials has the potential to transform 3D printing from a prototyping method into a robust manufacturing technique. However, there is no universally superior AM technique, and the most appropriate method must be selected for each application.

The Plasma Electrolytic Oxidation (PEO) process was investigated to enhance the adhesion of AA2024-O aluminum alloy with a polyetherimide (PEI) matrix composite, using oxy-fuel welding (OFW). A Central Composite Design (CCD) statistical model was used to optimize three independent parameters in PEO: immersion time (s), duty cycle (%), and electrolyte concentration (Na₂B₄O₇·10H₂O), aiming to achieve a maximum value of shear strength of the hybrid joint (in MPa). The hybrid joint without PEO treatment presented a resistance of 2.2 MPa while the best condition presented a resistance of 9.5 MPa, resulting in a value 4× higher than the untreated material, due to the characteristics of the coating, which presented a more hydrophilic surface, allowing better mechanical interlocking with the polymer matrix and resulting in mixed-mode failure (adhesive, cohesive, and light fiber). In addition to improving adhesion, the PEO treatment provided better corrosion resistance to the alloy, forming an inert aluminum oxide (Al₂O₃) coating, with an improvement of approximately 99.84% compared to the untreated alloy. The statistical design covers about 77.15% of the total variability of the PEO + welding process, with independent factors influencing around 48.4% of the variability.

In this study, the AA1100 aluminum alloy underwent the plasma electrolytic oxidation (PEO) process to enhance its adhesion to a thermoplastic composite of polyetherimide (PEI) reinforced with glass fiber, following ASTM D1002:10 standards. A 2³ factorial design was employed, varying three parameters in the oxidation process: immersion time, applied electric potential, and electrolyte concentration (Na₂B₄O₇). The joining of aluminum and thermoplastic composite samples was achieved through oxy-fuel welding (OFW), using oxygen and acetylene gases. For the characterization of the joined samples, a universal tensile testing machine was utilized with a displacement speed of 1.5 mm/min. The analysis of the oxide coating involved scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). Through variance analysis, it was determined that the statistical model encompasses approximately 80% of the variability in the adhesion process between materials. An improvement of up to 104% in adhesion between the materials was observed with the process, indicating an effective bond due to the presence of the thermoplastic matrix in the treated aluminum sample. This improvement is attributed to the morphology of the oxide coating, resembling corals, with micro-pores and recesses that facilitated mechanical anchoring.