The continuous increase in the consumption of aluminium and its alloys has led to an increase in the amount of aluminium scrap. Due to environmental protection, and to reduce the costs of manufacturing aluminum in recent years, a lot of research is devoted to recycling of aluminum alloys. The paper presents the results of research concerning the possibility of manufacturing standardized alloy 2017A from commercial and post-production scrap by continuous casting. Obtained from recycling process ingots were subjected to analysis of chemical composition and intermetallic phase composition. Based on the results of light microscopy (LM), scanning electron microscopy + electron dispersive spectroscopy (SEM + EDS), and X-ray diffraction (XRD) the following phases in the as-cast state were identified: θ-Al₂Cu, β-Mg₂Si, Al₇Cu₂Fe, Q-Al₄Cu₂Mg₈Si₇, and α-Al₁₅(FeMn)₃(SiCu)₂. During solution heat treatment most of the primary precipitates of intermetallic phases, like θ-Al₂Cu, β-Mg₂Si, and Q-Al₄Cu₂Mg₈Si₇, were dissolved in the solid solution α-Al, and during natural and artificial aging they precipitate as strengthening phases θ-Al₂Cu and Q-Al₄Cu₂Mg₈Si₇ with high dispersion. The highest hardness—150.3 HB—of 2017A alloy was obtained after solution heat treatment from 510 °C and aging at 175 °C. In the static tensile test the mechanical (R_m and R_p0.₂) and plastic (A₅) properties were determined for 2017A alloy in the cast state and after T4 heat treatment. The highest strength properties—tensile strength R_m = 450.5 MPa and yield strength R₀.₂ = 268.7 MPa with good relative elongation A₅ = 14.65%, were obtained after solution heat treatment at 510 °C/6 h/water quenching and natural aging at 25 °C for 70 h. The alloy manufactured from recycled scrap is characterized by relatively high mechanical properties.

Spent coffee grounds (SCG) have potential as a sustainable bio-filler in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composites, offering an environmentally friendly approach to waste utilization. This study investigated the effect of SCG content on the mechanical, thermal, and morphological properties of PHBV biocomposites and compared them with those of composites containing wood flour and hemp fibers. The biocomposites were fabricated via extrusion and injection molding, followed by the characterization of their mechanical performance, thermal behavior, and microstructure. The results indicated that SCG increased the stiffness of PHBV but did not enhance its tensile strength due to the weak interfacial adhesion between the filler and matrix. Unlike other lignocellulosic fillers, SCG requires lower processing temperatures, which is advantageous for thermally sensitive applications. SEM analysis revealed well-dispersed SCG particles at low concentrations, but visible aggregation and interfacial voids at higher loadings. While SCG serves as an effective and cost-efficient filler for improving the stiffness of PHBV, it does not reinforce the material in the conventional sense.

The production of thin-walled elements, especially those with large overall dimensions, poses numerous technological and operational problems. One of these problems relates to the machining-induced strain of such elements resulting from residual stress generated during the machining process. This study investigates the effect of the technological parameters of milling on residual stress in the surface layer of thin-walled plates made of aluminum alloy EN AW-2024 T351 for aerospace applications. The results have shown that residual stress increases with the cutting speed only to a certain point, reaching the maximum value at v_c = 750 m/min. At a cutting speed v_c = 900 m/min, residual stress significantly decreases, which probably results from the fact that the milling process has entered the High-Speed Cutting range, and this inference agrees with the results obtained for the cutting force component. Residual stress increases with the feed per tooth, while the relationship between residual stress and milling width is the same as that established for residual stress and variable cutting speed. Positive tensile stress is obtained in every tested case of the milling process. The results have also shown that the induced residual stress affects the strain of machined thin-walled parts, as proved by the strain results obtained for milled thin walls.

This study examines the impact of PVD coatings on cutting tool wear during the milling of 316L stainless steel under air cooling conditions. In the experiment, a carbide milling cutter coated with a nanocomposite nACo3 (AlTiSiN) coating was used. The coating was deposited using a next-generation device, the PLATIT π411PLUS, which features one central and three lateral rotating cathodes. The nanocomposite nACo3 coating obtained with this method exhibits exceptionally high structural density and excellent mechanical properties. The new generation of the nACo3 coating demonstrates improved surface properties and a lower friction coefficient compared to previous generations. The findings indicate that PVD nACo3 coatings significantly enhance wear resistance, extending tool life while maintaining acceptable surface quality. The optimal cutting time was determined to be approximately 90 min, after which a sharp increase in surface roughness and tool wear was observed. After 120 min of machining, substantial deterioration of surface quality parameters was recorded, suggesting increasing cutting forces and cutting edge degradation. SEM and EDS analyses revealed the presence of adhered material on the tool and sulfide inclusions in the microstructure of 316L stainless steel, which influenced the machining process. The nACo3 coating demonstrated high thermal and wear resistance, making it an effective solution for machining difficult-to-cut materials. This study suggests that selecting appropriate cutting parameters, tool geometry, protective coatings, and cooling strategies can significantly affect tool longevity and machining quality. The novelty of this research lies in the application of innovative nanocomposite PVD coatings during the milling of 316L stainless steel under air cooling conditions. These studies indicate potential future research directions, such as the use of minimum quantity lubrication (MQL) or cryogenic cooling as methods to reduce tool wear and improve post-machining surface quality.

This study investigated the effect of the recycling process on the microstructure, hardness, and precipitation kinetics of strengthening phases in the 2017A aluminum alloy. Light microscopy (LM) and X-ray diffraction (XRD) analyses revealed that the as-cast microstructure of the recycled 2017A alloy contained intermetallic phases, including θ-Al₂Cu, β-Mg₂Si, Al₇Cu₂Fe, Q-Al₄Cu₂Mg₈Si₇, and α-Al₁₅(FeMn)₃(SiCu)₂, and was comparable to that of the primary alloy, confirming its potential for high-performance applications. During solution heat treatment, most of the primary intermetallic precipitates, such as Al₂Cu, Mg₂Si, and Q-Al₄Cu₂Mg₈Si₇, dissolved into the solid Al matrix. DSC analysis of the solution-treated alloy established the precipitation sequence as follows: α-ss → GP/GPB zones → θ″ → θ′/Q′ → θ-Al₂Cu/Q-Al₄Cu₂Mg₈Si₇. The combined results from XRD, LM, TEM, and DSC confirmed that both θ and Q phases contributed to strengthening, with θ″ and θ′ phases playing a dominant role. Brinell hardness measurements during natural and artificial aging revealed that hardness increased with aging time, reaching a maximum value of 150.5 HB after ~22 h of artificial aging at 175 °C. The precipitation kinetics of the recycled 2017A alloy was studied via DSC measurements over a temperature range of ~25 to 550 °C, at heating rates of 5, 10, 15, 20, and 25 °C/min. The peak temperatures of clusters, GP zones, and hardening phases (θ′, θ″, θ, and Q) were analyzed to calculate the activation energy using mathematical models (Kissinger, Ozawa, and Boswell). The obtained values of activation energies of discontinuous precipitation were comparable across methods, with values for the θ″ phase of 89.94 kJ·mol⁻¹ (Kissinger), 98.7 kJ·mol⁻¹ (Ozawa), and 94.33 kJ·mol⁻¹ (Boswell), while for the θ′ phase, they were 72.5 kJ·mol⁻¹ (Kissinger), 81.9 kJ·mol⁻¹ (Ozawa), and 77.2 kJ·mol⁻¹ (Boswell). These findings highlighted the feasibility of using recycled 2017A aluminum alloy for structural applications requiring high strength and durability.