Jimy Unfried-Silgado

The influence of double continuous cold rolling followed by annealing on the texture evolution and mechanical properties of a commercial low-carbon ferritic steel was investigated. Ultrathin sheets (final thickness 0.22 mm) were produced through a two-stage cold rolling process with intermediate and final annealing at 690 °C for 35 s, followed by light temper rolling at 100 °C for 20 s. Texture evolution was characterized using Electron Backscatter Diffraction (EBSD) with Orientation Imaging Microscopy (OIM), producing pole figures and orientation distribution functions (ODFs). Mechanical properties were evaluated through Vickers microhardness and ultimate tensile strength measurements obtained from three independent locations per sample. Quantitative ODF analysis (φ₂ = 45°) revealed that γ-fiber ({111}//ND) intensity increased after each cold reduction stage and decreased after annealing due to recrystallization. The α-fiber (110/RD) and cube components (001//RD) showed a slight increase after annealing. The final ultrathin sheet exhibited moderate γ-fiber intensity (≈3 M.R.D), low Vickers microhardness (100–150 HV), and tensile strength (400–450 MPa). These results demonstrate controlled evolution of texture and microstructure during double cold rolling and annealing, providing a basis for future studies on forming-related behavior without directly assessing formability.

This study explores the use of banana pseudostem fibers from Córdoba, Colombia, as reinforcement in polymer composites manufactured through vacuum-assisted resin transfer molding (VARTM). The fibers were decorticated, oven-dried at 40 °C, and subjected to mercerization and epoxy coating treatments. Plain-weave fabrics were produced using continuous yarns composed of 10 and 15 fibers, both treated and untreated. Experimental analyses included pull-out tests, thermogravimetric analysis, fourier-transform infrared spectroscopy, winding speed, surface twist angle, and tensile strength tests for yarns, as well as tensile load, adhesion, and permeability tests for fabrics and tensile and flexural strength tests for composites. Treated yarns exhibited a slight increase in diameter and a lower extraction (25%) compared to untreated yarns (33%). Although treated fabrics showed enhanced permeability and improved resin infiltration, untreated fabrics demonstrated superior mechanical performance, with a tensile load of 2.33 kN in comparison to 1.37 kN for treated yarns. The highest tensile strength of 76.56 MPa was achieved in composites reinforced with three layers of untreated fabric, while the best flexural strength of 86.93 MPa was observed in single-layer composites with the same configuration. These results emphasize the potential of untreated banana fiber fabrics as promising reinforcement in structural composite applications.

In the present study, the effects of temperature and rotational and traverse speeds on the mechanical properties of polypropylene joints that are welded by friction stir welding using a non-rotational shoulder and a heat-assisted welding process is investigated. Tensile properties, microhardness measurements, microscopy observations, and thermal analysis are carried out in the present research to evaluate the effect of the welding parameters on the mechanical properties of welded joints. The experiments are conducted and analyzed by means of a central composite design using an analysis of variance (ANOVA). Variations in pre-heating temperature from 60 °C to 80 °C, rotational speed from 800 to 1500 rpm, and traverse speed from 20 mm/min to 100 mm/min are made for observations. A remarkable joint efficiency of 94% is achieved with joints that are free of discontinuities and defects. The fractured surfaces are observed to identify ductile and brittle zones. The crystallinity is measured, and a correlation between crystallinity and joint strength is discussed. The sample with highest efficiency shows 65% crystallinity and a ratio of 37.9% of ductile zone–total fractured area.

The influence of the process parameters, traverse, and rotational speeds of dissimilar friction stir welded joints of AA2024-O and AA6061-O aluminum alloys on the corrosion resistance was evaluated. Potentiodynamic tests using a 3.5% NaCl solution, open circuit potential, and polarization curves showed the corrosion behavior for the different welding parameters. These data were correlated with those obtained by mechanical tests (microhardness, tensile, and fracture analysis) and microstructure analysis by optical and scanning electron microscopy. It was observed that the combined effect of the parameters influenced the variation of corrosion resistance. This was evidenced mainly by the improvement of corrosion resistance at 1200 rpm–65 mm·min⁻¹, which was related to the tendency of grain size and heat input presented. The corrosive attacks on the welded joints presented greater affectations in the presence of base material 1 (AA6061-O) with higher metallic dissolution. Corrosion attacks abovementioned were presented in different forms, such as pitting, localized, and selective, and they were observed by scanning electron microscopy. Finally, in corrosive and mechanical terms, the best performing condition was 1200 rpm and 65 mm·min⁻¹ compared to the low parameter of 840 rpm and 45 mm·min⁻¹.

In this work, the adhesion behavior of chemically treated banana and coir Colombian fibers embedded in polylactic acid (PLA) and unsaturated polyester resin (UPR) matrices was investigated. Both types of fibers were treated with a 5 wt.% sodium hydroxide solution for one hour. The properties of treated and untreated fibers were determined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and tensile tests. To evaluate the adhesion behavior of the fibers in PLA and UPR matrices, pull-out tests were performed, and the percentage of broken fibers was determined. The results showed that alkaline treatment improved the fibers’ physicochemical, mechanical, and thermal properties. In addition, the alkaline treatment was able to improve the adhesion behavior of coir and banana fibers to PLA and UPR matrices. The banana fibers showed a percentage of broken fibers of 100%, while the coir fibers showed a slight increase in IFSS value. This behavior is attributed to the improvement in surface roughness due to the removal of non-cellulosic composites and impurities.

Friction stir welding (FSW) is a solid-state joining process that was developed and patented in 1991 by The Welding Institute [¹ 1 Thomas WM, Nicholas ED, Needham JC, Murch MG, Templesmith P, Dawes CJ. Inventor: Friction stir welding. United Kingdom patent GB2306366A. 1997 May 7. ]. Due to the highlighted manufacturing advances that the FSW process has achieved in recent years, important applications have been developed for welding alloys with good strength-to-weight ratios [² 2 Soori M, Asmael M, Solyall D. Recent development in friction stir welding process: a review. SAE International Journal of Materials and Manufacturing. 2020;14(1):63-80. http://doi.org/10.4271/05-14-01-0006. http://doi.org/10.4271/05-14-01-0006... ]. Several alloys, including aluminum alloys, have difficult weldability using conventional fusion welding processes. However, the FSW process has demonstrated the feasibility of joining these kinds of materials [³ 3 Isa MSM, Moghadasi K, Ariffin S, bin Muhamad MR, Yusof F, Jamaludin MF, et al. Recent research progress in friction stir welding of aluminium and copper dissimilar joint: a review. Journal of Materials Research and Technology. 2021;15:2735-2780. http://doi.org/10.1016/j.jmrt.2021.09.037. http://doi.org/10.1016/j.jmrt.2021.09.03... ]. The FSW process uses a tool consisting of a pin coupled to a shoulder. The tool rotates while it contacts the surface of the joint line of the components to be welded until the two parts of the tool come into simultaneous contact with the parts to be welded. Once the rotation and penetration of the tool are stabilized, it advances longitudinally along the welding line. The mixture and extrusion of plasticized material occurs due to the shoulder and pin friction [⁴ 4 Mishra RS, Ma ZY. Friction stir welding and processing. Materials Science and Engineering R Reports. 2005;50(1-2). http://doi.org/10.1016/j.mser.2005.07.001. http://doi.org/10.1016/j.mser.2005.07.00... ]. Currently, optimization strategies are being implemented in material selection for applications in the aerospace, marine, and automotive industries. New design challenges have led to the use of dissimilar aluminum joints to have better performance by combining properties of two different alloys and saving energy costs due to their good strength-to-weight ratio [⁵ 5 Patel V, Li W, Wang G, Wang F, Vairis A, Niu P. Friction stir welding of dissimilar aluminum alloy combinations: state-of-the-art. Metals. 2019;9(3):270. http://doi.org/10.3390/met9030270. http://doi.org/10.3390/met9030270... ]. However, despite the increasing use of these kinds of joints, several difficulties arise during and after the process, such as cracking, lack of fill, tunneling, or the formation of intermetallic compounds, which can be controlled by choosing suitable variables, such as rotational speed, traverse speed, positioning of the base materials, and tool geometry, among others [⁶ 6 Mastanaiah P, Sharma A, Reddy GM. Dissimilar friction stir welds in AA2219-AA5083 aluminium alloys: effect of process parameters on material inter-mixing, defect formation, and mechanical properties. Transactions of the Indian Institute of Metals. 2016;69(7):1397-1415. http://doi.org/10.1007/s12666-015-0694-6. http://doi.org/10.1007/s12666-015-0694-6... ].

Cashew nutshells from the northern region of Colombia were prepared to assess their potential use as a filler in polymer matrix filaments for 3D printing. After drying and grinding processes, cashew nutshells were characterized using scanning electron microscopy (SEM), attenuated total reflectance Fourier-transform infrared (ATR-FTIR), and thermogravimetric analyses (TGA). Three different filaments were fabricated from polylactic acid pellets and cashew nutshell particles at 0.5, 1.0, and 2.0 weight percentages using a single-screw extruder. Subsequently, single-filament tensile tests were carried out on them. SEM images showed rough and porous particles composed of an arrangement of cellulose microfibrils embedded in a hemicellulose and lignin matrix, the typical microstructure reported for natural fibers. These characteristics observed in the particles are favorable for improving filler–matrix adhesion in polymer matrix composites. In addition, their low density of 0.337 g/cm³ makes them attractive for lightweight applications. ATR-FTIR spectra exhibited specific functional groups attributed to hemicellulose, cellulose, and lignin, as well as a possible transformation to crystalline cellulose during drying treatment. According to TGA analyses, the thermal stability of cashew nutshell particles is around 320 °C. The three polylactic acid–cashew nutshell particle filaments prepared in this work showed higher tensile strength and elongation at break when compared to polylactic acid filament. The characteristics displayed by these cashew nutshell particles make them a promising filler for 3D printing filaments.

XIn this study, the influence of the process parameters, traverse and rotational speeds, of dissimilar friction stir welded joints of AA2024-O and AA6061-O aluminum alloys on the corrosion resistance was evaluated. Potentiodynamic tests using a 3.5% NaCl solution obtained open circuit potential curves and polarization curves showing the corrosion behavior for the different welding parameters. These data were correlated with those obtained by mechanical tests (microhardness, tensile, and fracture analysis) and microstructure analysis by optical microscopy and scanning electron microscopy. It was observed that the combined effect of the parameters influenced the variation of corrosion resistance. This was mainly evidenced by the improvement in corrosion resistance at 1200rpm − 65mm · min−1 which was related to the recrystallization of the grain size and the heat input presented. Corrosive attacks on the welded joints showed greater affectations in the presence of base material 1 (AA6061-O) with greater metallic dissolution. The attacks mentioned above were presented in different forms, such as pitting, localized, and selective, and were observed by scanning electron microscopy. Finally, in corrosive and mechanical terms, the best performing condition was 1200rpm − 65mm · min−1 compared to the low parameter 840rpm − 45mm · min−1 .