Search Results (266)

Shot-peening treatments improve the fatigue performance of mechanical components thanks to the surface modifications introduced and mainly due to the residual compressive stresses present in the layer of material near the shot-peened surface. There is no unanimous agreement in scientific literature regarding the kinetics of the damage process. However, it is generally accepted that, due to morphological and microstructural changes in the shot-peened layer, the material is more prone to early crack initiation, the propagation of which is then significantly slowed down or even stopped by the local stress field. This work focuses on applying the acoustic emission (AE) technique to detect fatigue crack initiation and propagation in shot-peened Al-alloy components. The analysis is conducted on Al-7075-T6 alloy, subjected to different shot-peening conditions and fatigue tested under alternating four-point bending. The results from the AE analyses are then correlated with a fractographic analysis. For all shot-peening conditions investigated, acoustic emission consistently indicated probable crack nucleation at approximately two-thirds of the total fatigue life, followed by a significant damage accumulation phase prior to dominant crack propagation. The final increase in acoustic activity coincided with the measurable loss of stiffness, confirming the onset of accelerated crack growth leading to fracture. The results demonstrate that, despite some experimental challenges, AE monitoring has the potential for the early detection of damage initiation. Full article

The influence of base plate temperature (25, 100, 200, and 400 °C) on the laser powder bed fusion processing of EN AW 7075 was systematically investigated using microstructural characterisation (LM, SEM, EBSD, GROD), chemical analysis, hardness testing, and thermal simulations across a broad range of process parameters. Moderate preheating at 100 °C and 200 °C showed no significant reduction in crack density or changes in grain morphology compared to processing without preheating. At the highest studied temperature—400 °C—a transition to columnar crack networks was observed, accompanied by modified grain orientation, pronounced stress relaxation, and reduced hardness. Independent of preheating temperature, consistent evaporation of Zn (~1 wt.%) and Mg (~0.3 wt.%) occurred during processing. Thermal simulations qualitatively supported the experimental observations, indicating increased thermal retention and displacement with increasing preheating temperature. The results demonstrate that base plate preheating alone is insufficient to suppress hot cracking in EN AW 7075 and may promote alternative crack-growth mechanisms at elevated temperatures, highlighting the need for alternative alloy or process design strategies. Full article

The AA7075 holds significant importance in the aerospace field. Understanding its microstructure evolution and constitutive relationships during warm deformation is crucial for optimizing forming processes. To this end, isothermal compression experiments were conducted at different temperatures and strain rates to analyze their flow stress behavior. The microstructure evolution was characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Microstructural analysis confirmed that dynamic recovery constitutes the predominant softening mechanism under warm forming conditions. The results indicate that flow stress is highly sensitive to deformation parameters, decreasing with increasing temperature and rising with increasing strain rate. To accurately describe the flow behavior, two distinct constitutive models were formulated: (1) a phenomenological Hensel–Spittel–Garofalo (HSG) model; (2) a novel hybrid machine-learning model that innovatively integrates the Harris Hawks Optimization (HHO) algorithm with an LSTM model. Both constitutive models demonstrate reasonable predictive accuracy. In comparison, the HHO-LSTM model demonstrated a superior ability to capture complex nonlinear relationships, achieving highly precise predictions of flow stress across the full range of deformation conditions tested in this work. The hybrid machine-learning model proposed in this study provides a highly accurate method for describing and predicting the flow behavior of the AA7075 during warm forming, offering a powerful predictive tool for engineering applications. Full article

This study investigated the structure of the decapod crustacean community in first- and second-order coastal rivers of the Atlantic Forest in southern Bahia, focusing on taxonomic composition, abundance, richness, and distribution of species. The main objective was to assess the possible effects of the severe drought of 2015, intensified by the El Niño event, on decapod species, also integrating analyses of land use and land cover by remote sensing. Collections were made in eight rivers between 2015 and 2017. In total, 7075 individuals of eight species were recorded, with Macrobrachium olfersii and M. jelskii being the most abundant in all seasons and locations sampled. Total abundance was higher in the rainy season, although the composition of the communities did not show significant differences between seasons. The Pancadinha and Represa rivers, which were most impacted, showed lower richness and absence of sensitive species such as Atya scabra, M. carcinus, M. heterochirus, and Trichodactylus sp. There were clear differences between impacted and unimpacted rivers. Land use classifications revealed marked changes between 2015 and 2016, with an increase in forest cover, especially in the northern zone. The results show that the combination of seasonality, environmental integrity, and land use shapes the dynamics of these communities. Full article

The pass reduction in hot rolling significantly influences the properties of 7075 alloy sheets, yet its quantitative effect requires systematic investigation. Multi-pass hot rolling experiments with 11% and 16% pass reductions were conducted on forged 7075 alloy. The microstructure, texture evolution, and mechanical properties were analyzed using SEM, EBSD, and mechanical testing. As the total thickness reduction increased, a clear correlation was observed with the enhanced mechanical properties of the hot-rolled 7075 alloy, demonstrated by the concurrent rise in both ultimate tensile strength (UTS) and yield strength (YS). When the total reduction exceeded 60%, the strengthening effect was most pronounced, with UTS and YS reaching 367.09 MPa and 332.82 MPa, respectively. The average grain sizes of 31.49 μm and 27.56 μm were achieved at the 12th pass (11% reduction per pass) and the 8th pass (16% reduction per pass), respectively. Under the condition of 11% reduction per pass, the texture intensity exhibited a non-monotonic trend with increasing passes. T6, T7, and RRA heat treatments were applied to the final rolled plates, and the maximum mechanical properties obtained in the hot-rolled 7075 plate following T6 heat treatment were UTS of 607.5 MPa, YS of 580.9 MPa, and elongation of 13.6%. Full article

This study investigates the microstructural evolution and wear behaviour of aluminium 7075-based metal matrix composites (MMCs) reinforced with high-entropy alloy (HEA) particles and fabricated via friction stir processing (FSP). A detailed characterisation of the grain refinement in the 7075 matrix was conducted, revealing significant dynamic recrystallization and grain size reduction induced by the severe plastic deformation inherent to FSP. The interaction between the matrix and HEA particles was analysed, showing strong interfacial bonding, which was further influenced by post-processing heat treatments. These microstructural modifications were correlated with the wear performance of the composites, demonstrating enhanced resistance due to the synergistic effect of precipitates and particle reinforcement. The findings highlight the potential of FSP as a viable route for tailoring surface properties in advanced MMCs for demanding tribological applications. Full article

This study established a marine atmospheric corrosion prediction model by comparing the corrosion behavior of 7075 aluminum alloy in neutral salt spray tests and outdoor exposure tests conducted in the coastal atmosphere of Hainan. The results show that severe rusting occurred after 96 h of neutral salt spray testing, with loose white cluster-like corrosion products mainly composed of Al(OH)₃ and Al₂O₃. The thickening of the corrosion product layer slowed down the corrosion process, following a nonlinear power-law kinetic relationship. In the later stage, potential dropped sharply due to product layer spallation, and recovered as new corrosion products formed, confirming that the stability of the product layer is critical for protection. Under coastal atmospheric exposure, the composition of corrosion products was similar to that observed in the salt spray test, but the actual corrosion rate was affected by environmental dynamic equilibrium. The acceleration factor of the neutral salt spray test corresponding to the same corrosion amount in the Hainan marine atmosphere exhibited a declining trend, reflecting that differences in the protective nature of the corrosion product layer were influenced by environmental factors. Electrochemical analysis indicated that both tests showed similar current–potential synergistic variation mechanisms dominated by product layer stability. In summary, while the neutral salt spray test effectively simulates the chloride-induced corrosion mechanism in marine atmospheres, its kinetic model cannot directly predict real corrosion behavior through a simple acceleration factor, as environmental complexity must be considered. Full article

The aim of this study was to evaluate the effect of heat treatment, including solutionising and ageing in the temperature range of 20–250 °C, on the microstructural, mechanical, and tribological properties of the Al 7075 alloy. Microscopic analysis revealed that in the as-received condition and after natural ageing, the microstructure is characterised by the presence of elongated grains and a banded distribution of precipitates, whereas higher ageing temperatures lead to their coarsening and the initiation of recrystallisation processes. The highest hardness (189 HV) was obtained after ageing at 100 °C for 48 h, while further increases in temperature caused a systematic decrease in hardness—down to 85 HV at 250 °C for 4 h. Impact tests showed that in the as-received condition, the material reached a value of 7 J/cm², after natural ageing 15 J/cm², and the maximum (26 J/cm²) was achieved for samples aged at 250 °C for 4 h. Tribological tests conducted using the T-07 method confirmed the dependence of wear resistance on heat treatment parameters—the lowest relative abrasive wear resistance coefficient was observed after natural ageing (k_b = 0.860), and the highest after ageing at 250 °C for 4 h (k_b = 1.216). The results obtained indicate that moderate ageing conditions (100–150 °C) favour increased hardness, whereas higher temperatures (200–250 °C) lead to an improvement in impact strength and tribological resistance, which showed an inversely proportional relationship with hardness, contrary to Archard’s law. Full article

Extrusion of AlZnMgCu alloys is associated with a very high plastic resistance of the materials at forming temperatures and significant friction resistance, particularly at the contact surface between the ingots and the container. In technological practice, this translates into high maximum extrusion forces, often close to the capacity of hydraulic presses, and the occurrence of surface cracking of extruded profiles, resulting in a reduction in metal exit speed (production process efficiency). The accuracy of mathematical material models describing changes in the plastic stress of a material as a function of deformation, depending on the forming temperature and deformation speed, plays a very important role in the numerical modelling of extrusion processes using the finite element method (FEM). Therefore, three mathematical material models of the tested aluminium alloy were analysed in this study. In order to use the results of plastometric tests determined on the Gleeble device, they were approximated with varying degrees of accuracy using the Hnsel–Spittel equation and then implemented into the material database of the QForm-Extrusion^® programme. A series of numerical FEM calculations were performed for the extrusion of Ø50 × 3 mm tubes made of 7075 aluminium alloy using chamber dies for two different billet heating temperatures, 480 °C and 510 °C, and for three different material models. The metal flow was analysed in terms of geometric stability and dimensional deviations in the wall thickness of the extruded tube and its surface quality, as well as the maximum force in the extrusion process. Experimental studies of the industrial extrusion process of the tubes, using a press with a maximum force of 28 MN and a container diameter of 7 inches, confirmed the significant impact of the accuracy of the material model used on the results of the FEM numerical calculations. It was found that the developed material model of aluminium alloy 7075 number 1 allows for the most accurate representation of the actual conditions of deformation and quality of extruded tubes. Moreover, the material data obtained on the Gleeble simulator made it possible to determine the limit temperature of the extruded alloy, above which the material loses its cohesion and cracks appear on the surface of the extruded profiles. Full article

The roll bonding of 7075/1060 composite laminates offers a promising approach toward the increase in toughness of aluminum layered composites. In this paper, 7075 and 1060 aluminum alloy plates were hot roll bonded to fabricate multilayered composite laminates. Solid solution at 470 °C for different holding times and subsequent aging were carried out for all the laminates. This study investigated the effect of holding times on the interfacial microstructure and interfacial bonding strength of the laminates. The interfacial shear strength was found to increase with longer holding times, which was attributed to the solid solution strengthening of the 1060 layer resulting from element diffusion. The findings also reveal that both tensile strength and toughness are positively correlated with the holding time of the solid solution, and there is a simultaneous improvement of tensile strength and toughness as the holding time increases. Microstructural characterization of the crack path profile of the Charpy impact and bending test indicates that interfacial delamination and main crack deflection become pronounced with the increase in holding time, and these lead to an increase in the fracture resistance in the crack-arrester orientation. Full article

This work quantifies the environmental sensitivity of tartaric–sulfuric acid (TSA) anodized and sealed 6061 and 7075 aluminum. Five alloy–temper states (6061-T4, 6061-T62, 7075-T0, 7075-T62, and 7075-T73) were TSA-treated, pore sealed and then exposed for eight weeks (56 days) to ambient air, 11 wt.% NaCl brine, or a microbiological medium, with weekly +20 °C/−20 °C freeze–thaw cycles. Tensile tests assessing yield strength, ultimate strength, and elongation were conducted. Strength losses were modest in ambient conditions (<5%) but increased to ≈5–10% for yield and ≈2–9% for ultimate under saline and microbial conditions, particularly in the annealed 7075-T0 and peak-aged 7075-T62 states. Ductility was more sensitive, declining up to ≈30% for 6061-T4 and 6061-T62 in harsh media. Permutation-based inference within an additive screening model indicated that environmental exposure is strongly associated with the dominant share of the observed variability (R²_env ≈ 0.91–0.93 for yield, ultimate strength, and elongation), within the limits of the present dataset. These results suggest that freeze–thaw cycling, chloride exposure, and microbiological activity are consistent with the observed degradation trends. Over-aged 7075-T73 retained properties better than T62, highlighting the roles of temper and pore sealing quality in cold, saline, and microbiologically active service. Full article

Micro milling of metallic materials presents unique dynamic challenges due to highly nonlinear cutting forces and the susceptibility to self-excited vibrations (chatter). This paper presents a novel mathematical model for chatter prediction in micro milling, based on an enhanced formulation of cutting forces that includes the frictional interaction between the tool’s flank face and the machined surface. The proposed approach enables accurate simulation of the cutting process and prediction of the limiting depth of cut, beyond which chatter occurs. Experimental validation was performed using pneumatic spindle and micro end mills, with chatter detection based on surface inspection via digital microscopy. A strong correlation was observed between the simulated and experimentally determined limiting depths of cut, confirming the model’s predictive capability. This research offers a new methodology for modelling cutting forces and improves the ability to predict chatter in micro milling processes, contributing to the optimization of machining parameters across a wide range of materials. Full article

This study investigates the effects of welding current on the microstructure, mechanical properties, and corrosion behavior of 7075/7075 pulsed metal inert gas (P-MIG) welded joints. Welding experiments were conducted at currents of 190 A, 200 A, and 210 A using ER5356 filler wire, with the joints analyzed through optical microscopy (OM), scanning electron microscopy (SEM/EDS), and tensile and hardness testing, as well as intergranular and electrochemical corrosion evaluations. The results reveal that increasing welding current alters the solidification dynamics and precipitation behavior in the WZ. At 190 A, refined and uniformly distributed dendrites were obtained, whereas at 210 A, grains coarsened and elemental segregation was more pronounced. The weld hardness exhibited a trend of first increasing and then slightly decreasing with increasing welding current, with a maximum value of 99.5 HV0.1 obtained at 200 A. Similarly, the tensile strength improved with increasing welding current, reaching 257.7 MPa with 8% elongation at 210 A. Corrosion resistance exhibited a non-monotonic trend, with the best performance observed at 200 A, as indicated by the shallowest intergranular corrosion depth, the most positive open-circuit potential, and the highest charge transfer resistance in electrochemical impedance spectroscopy. The findings demonstrate that welding current is a critical parameter controlling the balance between microstructural refinement, mechanical strengthening, and corrosion resistance, and that 200 A represents the optimal condition under the investigated parameters. These insights provide theoretical guidance and experimental evidence for process optimization in the welding of high-strength aluminum alloys. Full article

Large Strain Extrusion Machining (LSEM) is an intensive plastic deformation process evolved from conventional machining, enabling effective control over chip morphology and grain refinement. This process often generates high cutting temperatures and frictional instability during machining, which degrades material properties and accelerates tool wear. This study proposes a technique combining microtextured tools with LSEM to optimize cutting performance. By designing different microtextured tools (parallel-to-cutting-edge microtextured tools (P-T) and perpendicular-to-cutting-edge microtextured tools (V-T)), cutting experiments were conducted on 7075 aluminum alloy to systematically investigate the effects of microtextured LSEM on cutting performance and chip formation. Results indicate that microtextured tools effectively reduce cutting temperatures. Compared to non-textured tools (N-T), microtextured tools can lower maximum cutting temperatures by up to 13.20% (36.56 °C). Microtextured LSEM suppresses serration formation, leading to more stable chip formation. The serration degree of chips produced by microtextured tools was reduced by up to 25.66% compared to N-T tools. XRD analysis indicates that microtextured tools significantly increase chip dislocation density, reaching nearly 2.77 times that of N-T tools, enhancing material microhardness and refining grain size. This study confirms that combining microtextured tools with LSEM synergistically optimizes chip morphology and improves the microstructural properties of Al7075, providing technical support for machining high-strength aluminum alloys. Full article

The 2000 series aluminium alloys are an attractive option for lightweight structures, but solidification cracking in fusion welding remains an issue in additive manufacturing technologies. Al-Cu-Li alloys, in particular, have gained considerable attention due to their excellent strength-to-weight ratio and corrosion and fatigue resistance, making them highly suitable for aerospace components. Nevertheless, their narrow solidification range makes them highly susceptible to cracking, porosity formation, and elemental evaporation during fusion-based AM processes. These challenges underscore the necessity for advanced processing technologies and the development of suitable feedstock materials to ensure weld integrity and optimal performance. Although Al–Cu–Li alloys are highly valued in the aerospace sector, the application of wire arc additive manufacturing (WAAM) is currently limited by the lack of commercially available wire compositions. This study focuses on the use of powder metallurgy Al-Cu-Li wires in wire arc additive manufacturing, specifically using plasma metal deposition technology, to explore welding characteristics. This research demonstrates the development of an alternative wire using powder metallurgy for WAAM. Powder metallurgy wires were deposited on 5053 and 7075 aluminium substrates, and their microstructure, chemical composition, and mechanical properties were analysed. Key findings include significant elemental losses of Li and Cu during deposition—approximately 55% and 25%, respectively—as well as noticeable variations in microstructure, porosity, and grain morphology, depending on the substrate. Deposits on the 5083 aluminium exhibited more equiaxed grains and a higher chemical homogeneity compared to those on the 7075 substrate. This work establishes a link between material design and additive manufacturing by demonstrating that powder metallurgy Al–Cu–Li wires can be effectively processed by WAAM, achieving controlled elemental losses and a uniform microstructure that enhances weld integrity in aerospace components. Full article