Plasma Electrolytic Oxidation (PEO) as a Promising Technology for the Development of High-Performance Coatings on Cast Al-Si Alloys: A Review

Abstract

Cast Al-Si alloys, recognized for their excellent mechanical properties, constitute one of the most widely employed non-ferrous substrates in several sectors, and are particularly relevant in the transport industry. Nevertheless, these alloys also display inherent limitations that significantly restrict their use in several applications. Among these limitations, their low hardness, low wear resistance, or limited anti-corrosion properties, which are often not enough when the component is subjected to more severe environments, are particularly relevant. In this context, surface modification and the development of coatings are essential for the application of cast Al-Si alloys. This review focuses on the development of coatings to overcome the complexities associated with improving the performance of cast Al-Si alloys. Against this background, plasma electrolytic oxidation (PEO), an advanced electrochemical treatment that has revolutionized the surface modification of several metallic alloys in recent years, emerges as a promising approach. Despite the growing recognition of PEO technology, the achievement of high-performance coatings on cast Al-Si is still a challenge nowadays, for which reason this review aims to provide an overview of the PEO treatment applied to these alloys. In particular, the impact of the electrolyte chemical composition on the properties of the coatings obtained on different alloys exposed to harsh environments has been analyzed and discussed. By addressing the existing gaps and challenges, this paper contributes to a better understanding of the intricacies associated with the development of robust PEO coatings on cast Al-Si alloys.

Possibility of Phase Transformation of Al2O3 by a Laser: A Review

“…The PEO process is performed at high voltage (up to 700 V), resulting in the formation of electrical micro-discharges caused by the localized dielectric breakdown of the growing oxide coating, which determines the structure, morphology, and phase composition of the coating. The PEO process involves three simultaneous operations: electrochemical reactions, plasma-chemical reactions, and thermo-chemical reactions [60]. PEO coatings typically exhibit a morphological structure characterized by three distinct layers [60,61].…”

“…The PEO process involves three simultaneous operations: electrochemical reactions, plasma-chemical reactions, and thermo-chemical reactions [60]. PEO coatings typically exhibit a morphological structure characterized by three distinct layers [60,61]. The outer layer, constituting approximately 5% to 30% of the coating thickness, often displays defects such as cracks and pores.…”