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The purpose of this paper is to study how cryogenic CO₂ cooling during the welding process affects corrosion behaviour of friction stir welding (FSW) AA7010‐T7651.

Friction stir welded AA7010‐T7651 was produced with a rotation speed of 288 rpm and a travel speed of 58 mm/min. The liquid CO₂ was sprayed onto the weld centre line immediately after the toolpiece. The microstructures of welds in different regions were observed using Field Emission Gun Scanning Electron Microscope (FEG‐SEM). The effect on the corrosion susceptibility was investigated using a gel visualisation test and potentiodynamic polarisation measurements using a micro‐electrochemical technique.

The main corrosion region for both FSWs AA7010‐T7651 produced with and without cryogenic CO₂ cooling is in the HAZ region, which exhibited intergranular attack. Cryogenic cooling does not show any influence on anodic reactivity of the weld region (both nugget and HAZ) compared to uncooled weld metal. However, the width of the reactive HAZ is reduced after cooling, as compared to the uncooled weld. The cooled welds show higher cathodic reactivity in the nugget region than does the nugget region of uncooled welds.

There has been no previous work to investigate the effect of cryogenic CO₂ cooling on the corrosion behaviour of FSW AA7010‐T7651. The paper relates the microstructures of both uncooled and cooled welds to their anodic and cathodic reactivities using a micro‐electrochemical technique.

The purpose of this paper is to understand the effect of pressurized steam on surface changes, structures of intermetallic particles and corrosion behavior of AA1050 aluminium.

Industrially pure aluminium (AA1050, 99.5 per cent) surfaces were exposed to pressurized steam produced from a commercial pressure cooker at the maximum temperature of 116oC for 10 min. Surface morphology was observed using SEM‐EDX and FIB‐SEM. Phase identification and compositional depth profiling were investigated using XRD and GDOES, respectively. Potentiodynamic polarization measurements were used to study corrosion behavior.

A 590 nm boehmite oxide layer was generated on AA1050 associated with partially dissolved and/or fallen off Fe‐containing intermetallic particles after exposure to pressurized steam. A significant reduction (25 times) in anodic and cathodic reactivities was observed due to the formation of the compact oxide layer.

This paper reveals a detailed investigation of how pressurized steam can affect the corrosion behaviour of AA1050 aluminium and the structure of Fe‐containing intermetallic particles.

The purpose of this investigation is to understand the structure of trapped intermetallics particles and localized composition changes in the anodized anodic oxide film on AA1050 aluminium substrates.

The morphology and composition of Fe‐containing intermetallic particles incorporated into the anodic oxide films on industrially pure aluminium (AA1050, 99.5 per cent) has been investigated. AA1050 aluminium was anodized in a 100 ml/l sulphuric acid bath with an applied voltage of 14 V at 20°C ±2°C for 10 or 120 min. The anodic film subsequently was analyzed using focused ion beam‐scanning electron microscopy (FIB‐SEM), SEM, and EDX.

The intermetallic particles in the substrate material consisted of Fe or both Fe and Si with two different structures: irregular and round shaped. FIB‐SEM cross‐sectioned images revealed that the irregular‐shaped particles were embedded in the anodic oxide film as a thin strip structure and located near the top surface of the film, whereas the round‐shaped particles were trapped in the film with a spherical structure, but partially dissolved and were located throughout the thickness of the anodic film. The Fe/Si ratio of the intermetallic particles decreased after anodizing.

This paper shows that dual beam FIB‐SEM seems to be an easy, less time consuming and useful method to characterize the cross‐sectioned intermetallic particles incorporated in anodic film on aluminium.

Friction stir welding (FSW) and underwater friction stir welding (UWFSW) of aluminium alloy 2024-T351 was carried out, with a chosen set of parameters, namely, rotational speed of 450 rpm, 560 rpm and 710 rpm, welding speed of 25 mm/min, 40 mm/min and 63 mm/min and tool tilt angle of 0º, 1° and 2º. This study aims to understand the correlation between temperatures and weld parameters, finite element simulation was carried out using Abaqus®.

Comparative analysis of the mechanical properties of the samples welded with FSW and UWFSW was carried out and correlated with that of the microstructures. Microhardness survey was also conducted across the weldments to support the findings.

Samples welded with higher rotational speed and low traverse speed favoured good quality, defect-free welds with enhanced material flow. Underwater welded samples resulted in improved mechanical properties than that of the samples welded with conventional FSW. Higher cooling rates resulted in finer grains in all UWFSW samples than that of conventional FSW samples, which, in turn, also reflected in the microhardness survey done across the weldments. Among the chosen window of the parameter, samples welded with 710 rpm, 25 mm/min and 2° had shown improvement in mechanical properties.

This work was carried out in a milling machine, which limits the rotational speed which could be used. Optimistically, this limitation also paves way for using the commonly available milling to be used for FSW.

This original research study shall open opportunities to enable FSW and UWFSW to be done on similar/dissimilar joints of varying composition. Additionally, this research study throws enough light on the age – hardenable aluminium alloy being welded in a commonly available milling machine.

This paper aims to overcome the corrosion in AA7075 by incorporating the dual-reinforcements like Al2O3 and SiC through friction stir processing (FSP). In recent days, an automotive monocoque structure undergoes corrosion because of changes in environmental conditions.

Surface hybrid composites (SHCs) of AA7075 with different weight ratios of Al₂O₃ and SiC were fabricated at a rotating speed of 1000 rpm, traveling speed of 56 mm/min and tool tilt angle of 2º with two passes. Surface regions were observed using optical microscopy, and the potentiodynamic corrosion test was performed under a 3.5 per cent NaCl environment at room temperature. Then, the surface morphology analysis of corroded samples and their structural properties were also investigated through scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron dispersive spectroscopy (EDS).

Through FSP, an improved interface between the reinforced particles and the AA7075 base matrix was observed because of the severe plastic deformation. Potentiodynamic polarization tests confirmed that the AA7075 matrix with a higher concentration of Al₂O₃ and a lower concentration of SiC (Al₂O₃ – 75 per cent and SiC – 25 per cent) possesses a lower corrosion rate than other specimens. This result is because of the combined effect of stable passive film formation and the resistance produced by hard SiC particles. In addition, the formation of a stronger interface between the reinforcements and the base matrix impedes the NaCl solution attack. The SEM micrograph depicts the film crystallinity variations with an increase in Al₂O₃ content. Debonding between the layers was observed on increasing the SiC content in the base matrix. XRD shows the peaks of reinforcing elements that influence the corrosion behavior. These observations suggest that the AA7075 reinforced with a higher concentration of Al₂O₃ and a lower concentration of SiC through FSP affords a suitable solution for automotive monocoque applications.

The corrosion rate has been identified for AA7075 SHCs with various concentrations of Al₂O₃ and SiC and has been compared with that of the base metal and the friction stir processed specimen without reinforcement.

The aim of this work was to investigate how Andrographis paniculata (Burm.f.) Wall.ex Nees extract affected the corrosion of low-carbon (C) steel in 0.1M HCl.

The Andrographis paniculata (Burm.f.) Wall.ex Nees was extracted into distilled water at 70°C for 1 h. The corrosion inhibition efficiency of the extract was determined in 0.1M HCl using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. The effects of extract concentrations and of temperature were investigated.

The Andrographis paniculata (Burm.f.) Wall.ex Nees extract could inhibit the corrosion process of low-C steel in 0.1M HCl. With the extract concentration of 1 g/l, an inhibition efficiency of 96.3 per cent was obtained. The extract acted as an anodic inhibitor. The adsorption process of the extract was physisorption and it followed the Langmuir adsorption isotherm.

This paper revealed that Andrographis paniculata (Burm.f.) Wall.ex Nees cultivated in Thailand, which was extracted using a simple and environmentally friendly method, could act as a very good green corrosion inhibitor for low-C steel in 0.1M HCl solution.