Corrosion inhibitors have traditionally been utilised to protect copper alloy sculptures from corrosion despite the recognised environmental and human health risks. Knowing the associated toxicity, ongoing extensive research seeks alternative substances for corrosion reduction, giving rise to the emergence of green inhibitors. In this pursuit, plant extract inhibitors have gained attention, particularly in the heritage field. This review discusses recent advancements in synthesising sustainable and eco-friendly products designed to preserve metallic heritage from corrosion. We discuss the key findings on plant extracts used for corrosion control in metal alloys, taking into account the extraction methods to ensure the comprehensive coverage of relevant details. The use of plant extracts as corrosion inhibitors for metallic materials in cultural heritage (CH) is a highly promising and valuable research area. This review highlights recent advancements in the field, providing utility for conservators, conservation scientists, and restorers in identifying the most effective, eco-friendly, and safe compounds for material application.

Advanced high-strength steels (AHSSs) are designed for meeting strict requirements, especially in the automotive industry, as a means to directly influence the reduction in the carbon footprint. As rotary friction welding (RFW) has many important advantages over other welding technologies, it plays an important role in the automotive sector. On the above basis, in this work, combinations of the first (complex phase (CP)), second (TWIP (TW)), and third (quenched and partitioned (Q&P)) generations of similar and dissimilar high-alloyed advanced steels have been joined by the RFW process. Having a specific microstructure, rods of CP/CP, Q&P/Q&P, CP/TW, and Q&P/TW steels were welded by employing a homemade adaptation machine under fixed parameters. Microstructural characterization has allowed us to corroborate the metallic bonding of all the tested advanced steels and to identify the different zones formed after welding. Results indicate that the welding zone widens in the center of the workpiece, and under the current friction action, the intermixing region shows the redistribution of solute elements, mostly in the dissimilarly welded steels. Furthermore, because of their complex chemistry and the different mechanical properties of the used steels, dissimilarly welded steels present the most noticeable differences in hardness. The TWIP steel has the lower hardness values, whilst the CP and Q&P steels have the higher ones. As a direct effect of the viscoplastic behavior of the steels established by the thermomechanical processing, interlayers and oxidation products were identified, as well as some typical RFW defects. The electrochemical response of the welded steels has shown that the compositional and microstructural condition mostly affect the corrosion trend. This means that the dissimilarly welded steels are more susceptible to corrosion, especially at the TWIP–steel interface, which is attributed to the energy that is stored in the distorted microstructure of each steel plate as a consequence of the thermomechanical processing during RFW.

The objective of this research work is to obtain the hot ductility behavior, and the structural, microstructural and mechanical characteristics of one of the latest generation of AHSS steels, a complex phase (CP) steel microalloyed with boron (0.006 wt.%), processed by hot and cold rolling operations and heat-treated using two different quenching and partitioning (Q&P) treatments, a one-step partitioning (quenching to 420 °C) and the other a two-step partitioning (quenching to 420 °C and reheated to 600 °C). The results show that boron has a marked effect on the solidification process of the CP steel, refining the austenitic grain size. Due to its refinement, the boron-containing steel had better ductility throughout the temperature range examined (700–900 °C), i.e., the hot ductility trough. Thus, the minimum percentage of reduction in area (%RA) value occurring at 800 °C was 43% for the boron-free steel, compared with 58% for the boron-containing steel. Hence, cracking would not be a problem when straightening the strand on continuous casting. The benefit of boron addition on the room temperature properties was found to be very marked for the higher temperature two-step partitioning treatment, giving a yield stress of 1200 MPa, a UTS (ultimate tensile strength) of 1590 MPa and a total elongation above 11%. The final Q&P microstructure, in both one- and two-step partitioning conditions, consisted of retained austenite (RA-γ), martensite and ferrite islands in a bainitic matrix. Furthermore, the boron treated steel on quenching produced a greater amount of RA-γ, which accounted for its better room temperature ductility and produced a martensitic matrix rather than a bainitic one, giving it greater strength. The addition of boron improved the corrosion resistance of this type of third generation AHSS steel.

The bronze patina is aesthetically pleasing and enhances the corrosion resistance of the metallic object. This corrosion product layer can develop naturally, through aging or artificially. However, artificial methods require substances that are hazardous to human health and the environment. In this study, a sustainable approach to patina development, based on the anodic polarization of a 85.5Cu-4.2Pb-4.5Sn-5.7Zn copper alloy immersed in 0.1 M NaCl + 0.01 M NaHCO₃ were characterized using polarization curves, chronoamperometry, electrochemical impedance spectroscopy, electrochemical noise measurements, X-ray diffraction, and scanning electron microscopy. The results indicate that the anodic potential modifies the current density as well as the diffusion coefficient of oxygen associated with a thicker corrosion product layer. Electrochemical Impedance spectroscopy and electrochemical noise show that the porous behaviour and corrosion resistance increases as the potential becomes more anodic due to the formation of a protective layer. This behaviour corresponded with the results acquired by chronoamperometry. The surface characterization shows that the potential applied changes the surface morphology and composition of the corrosion products, being identified the crystalline phases of nantokite and atacamite although Cu, Cl, O, Zn, and Pb elements were also detected.

Lead-free solders are promising candidates for the replacement of Sn–Pb solders due to their environmental friendly, good thermal properties and wettability which render them suitable for this application. In this study, a set of lead-free solders Sn-6.5 wt. and Sn-6.5 wt% Zn-0.5 wt% X (X = Ag, Al, Cu) were studied by metallography, mechanical and electrochemical techniques. The results show that the addition of the alloying elements Ag, Al and Cu modifies the amount of the eutectic phase and promotes the formation of intermetallic compounds (IMCs). The corrosion resistance of the samples also modified, showing that the formation of IMCs can have detrimental effects with higher current densities in saline media, as determined for the Ag and Al alloyed solders. The corrosion resistance is higher for the unalloyed and the Sn-6.5 wt%Zn-0.5 wt% Cu alloy. However, the addition of Cu not only stabilizes the corrosion products thus increasing the protective properties of the alloy, but also modifies the mechanical behaviour of the lead-free solders and so enhancing the UTS values and ductility. Furthermore, the surface morphology is influenced by the alloying elements showing a smooth surface (Sn-Zn, Cu) or a highly corroded appearance with round aggregates (Ag and Al). These new lead-free solders have a lower melting point with higher ductility than the commercial SAC 305. Therefore, these alternatives have high potential in applications in mechanical engineering.

The growth of patinas on artistic or archeological copper alloys is a determining stage to reproduce similar surface conditions such as corrosion protection of cultural heritage materials. In this work, the kinetic growth and protective properties of the corrosion products layer of a quaternary copper alloy have been characterized using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy‐EDS, atomic force microscopy, X‐ray diffraction, and Raman spectroscopy. The results of LSV show that the patina formation is a mixed process consisting of dissolution and direct film formation. EIS results show that the kinetic formation modifies the characteristics of the corrosion layer allowing a Warburg‐like diffusive mechanism or the response of a porous oxide layer without diffusive phenomena. The roughness and thickness of the patina enhance with the decrease in the scan rate. The patina is mainly composed of copper and tin corrosion products.