This study’s novelty lies in providing first-time insights into the isolated role of Friction Stir Processing (FSP) travel speed on microstructure evolution and mechanical performance (micro-hardness, tensile properties, impact energy, and wear behavior) specifically in hypoeutectic as-cast Al-5 wt.% Si alloys, addressing a critical unaddressed gap in previous works (typically on near-eutectic compositions of Si > 6.5 wt.%). FSP, a solid-state technique, is highly effective for enhancing the properties of cast materials. The FSP was conducted at a fixed rotational speed of 1330 rpm and various travel speeds (26, 33, 42, and 52 mm/min). The FSP improves the mechanical properties of as-cast Al-5Si alloy by refining its grain structure. This leads to higher hardness, ultimate tensile strength (UTS), yield strength (YS), and strain at fracture and toughness compared to the as-cast condition. The specimen processed at 26 mm/min achieved the highest values of YS, UTS, toughness, and wear resistance. The fracture surfaces of the tensile and impact test specimens were examined using scanning electron microscopy (SEM) and discussed. Results indicated that the fracture surfaces revealed a transition from predominantly brittle fracture in the as-cast alloy to ductile fracture at 26 mm/min, changing to a mixed fracture mode at 52 mm/min. These findings underscore the critical importance of optimizing FSP travel speed to significantly tailor and enhance the mechanical performance of as-cast hypoeutectic Al-5Si alloys for industrial applications.

This study explores Friction Stir Spot Welding (FSSW), a well-established solid-state joining technique, for high-strength aluminum alloys like AA2024-T4, which present significant challenges for conventional welding techniques. This research focuses on the impact of relatively low rotational speeds, specifically within a range of 700 to 1300 rpm, on the mechanical and microstructural properties of the welded joints. By employing a short dwell time of 3 s, this study aims to enhance productivity in the automotive and aerospace industries. The experimental work evaluated the joints’ thermal cycles, macrostructure, microstructure, hardness and load-carrying capacity. Results indicated a linear relationship between rotational speed and heat input. Although all welds exhibited a significant grain size reduction in the stir zone (SZ) compared to the base material (29.7 ± 6.1 μm), the SZ grain size increased with rotational speed, ranging from 4.7 ± 1.4 to 8.3 ± 1.3 μm. This study identified 900 rpm as the optimal parameter, achieving the highest load-carrying capacity (7.35 ± 0.4 kN) and a high SZ hardness (99 ± 1.5 HV). These findings confirm that joint strength is a balance between grain refinement and thermal softening. The presence of precipitates and the fractography of the tensile–shear tested specimens were also investigated and discussed.

The growing volume of plastic waste produced has made the need for efficient identification and quantification strategies to detect and identify harmful contaminants, particularly heavy-metals, in industrial plastic-waste streams more urgent than ever. Traditional chemical digestion methods (acid digestion, ICP-MS, or AAS) provide accurate quantification and are time-consuming, costly, and not high-throughput-sorting. Laser-induced breakdown spectroscopy (LIBS) offers several advantages, including rapid real-time analysis, minimal sample preparation, multi-element detection, and efficient elemental characterization. The current review aims to investigate the possibility of using the LIBS technique to detect and quantify some heavy-metals like lead (Pb), cadmium (Cd), chromium (Cr), and arsenic (As) in heterogeneous industrial plastic wastes. The calibration strategies (reference standards) as well as optimization of the signal response and algorithms for data processing, including chemometric models, are evaluated to reduce the limit of detection and enhance analytical accuracy. The results indicate that LIBS can detect heavy-metal contamination at concentrations relevant to regulatory limits and can be scaled for online quality-control monitoring in plastic recycling facilities. In this review, the results have been summarized to support the use of LIBS for waste management towards environmental compliance, reduced use of hazardous materials in recycling products, and reduced health problems due to heavy-metal pollution.