Search Results (42)

The hot deformation behavior of 7050 aluminum alloy was investigated by isothermal compression tests over a temperature range of 250 °C to 450 °C and a strain-rate range of 0.001 s⁻¹ to 1 s⁻¹. The flow stress was strongly dependent on both temperature and strain rate. At a strain rate of 0.1 s⁻¹, increasing the temperature from 250 °C to 450 °C reduced the peak stress by 72.7%. At 450 °C, decreasing the strain rate from 1 s⁻¹ to 0.001 s⁻¹ reduced the peak stress from 66.7 MPa to 14.6 MPa, corresponding to a decrease of 78.1%. Based on the peak stress, an Arrhenius-type constitutive equation was established, with a deformation activation energy of 179.35 kJ mol⁻¹. The predicted peak stresses agree well with the experimental values, giving a correlation coefficient (R²) of 0.98. The processing map indicates that the optimal hot working domain is located at 400–450 °C and 0.001–0.05 s⁻¹. Scanning electron microscopy (SEM) observations showed that increasing temperature promoted the reduction in second-phase particles, with their area fraction decreasing from 5.3% at 250 °C to 1.2% at 450 °C under 0.001 s⁻¹. In comparison, strain rate had a smaller effect on the particle area fraction at 450 °C. Electron backscatter diffraction (EBSD) analysis revealed that high temperature and low strain rate enhanced dynamic recovery and grain-boundary misorientation evolution. The fraction of low-angle grain boundaries (LAGBs) decreased from 71.5% to 38.8% as the temperature increased from 250 °C to 450 °C under 0.001 s⁻¹, and decreased from 48.2% to 38.8% when the strain rate decreased from 1 s⁻¹ to 0.001 s⁻¹ at 450 °C. Full article

To accurately control the hot workability of 7050 aluminum alloy and determine the optimal process window, systematic hot compression experiments were carried out on the Gleeble-3500 thermal simulation test machine under the multi-group process conditions of deformation temperature 300~450 °C, strain rate 0.001~1 s⁻¹, and maximum deformation of 60%. The high-temperature rheological curve data were collected, and the key hot deformation parameters, such as deformation activation energy Q, Zener–Hollomon (Z) parameter, and power dissipation efficiency η, were calculated based on the experimental results. The random forest prediction model between process parameters and thermal deformation parameters was innovatively constructed to realize the accurate quantification of the parameter relationship. On this basis, the multi-objective process optimization was further carried out by coupling the TOPSIS and EWMs. Finally, the optimal hot deformation process parameters of 7050 aluminum alloy were determined as 410~450 °C and 0.001~1 s⁻¹. The microstructure analysis showed that the main deformation mechanism of the material in the optimized region was dynamic recrystallization, which could effectively ensure the microstructure uniformity and mechanical property stability of the formed parts. Full article

In this work, the effect of Fe and Si content on microstructure, mechanical properties, and corrosion resistance of 7050 alloy was systematically investigated by room temperature tensile, fracture toughness, and exfoliation corrosion tests, complemented by microstructural characterization through SEM and TEM. The results demonstrate that the impurity elements Fe and Si induce the formation of insoluble Fe-rich phases and Mg₂Si phases in the alloy, respectively. The coexistence of Fe and Si leads to a severe synergistic deterioration effect on mechanical properties. Furthermore, the study reveals that Si has a more profound negative impact on mechanical properties than Fe. While Fe primarily reduces ductility and fracture toughness by initiating microcracks through Fe-rich phases with minimal effect on strength, Si not only forms brittle Mg₂Si phases that impair toughness but also significantly depletes the Mg content in the matrix, thereby reducing the quantity of strengthening phases. This results in a comprehensive and severe decline in strength, plasticity, and toughness. In addition, Fe and Si impurities markedly degrade the exfoliation corrosion resistance of the alloy. Full article

The objective of the study was to determine the minimum thickness of a thin wall for milling at a maximized axial depth of cut, considering the effect of cutting speed on residual stress and post-machining distortion. Test samples were made of aluminum alloy 7050 T7451. The milling operation at a maximized axial depth of cut was performed during finishing. Response surface methodology was employed. Wall thickness and cutting speed were considered as two independent variables, while dependent variables were flatness deviation, wall thickness deviation, and residual stress. Flatness deviation and wall thickness deviation were used as the indicators of post-machining wall deformation and their measurements were made using a coordinate measuring machine. Residual stress was measured with an X-ray diffractometer. The obtained results showed that thin wall milling at a maximized axial depth of cut was feasible; nevertheless, for a wall thickness of t = 1 mm, the formation of considerable post-machining deformation was observed. Therefore, for milling with the employed axial depth of cut, the wall thickness should be t ≥ 1.5 mm. The highest strain and residual stress were observed at v_c ≈ 600 m/min; despite its subsequent decrease, the strain at v_c = 900 m/min was still higher than that at v_c = 300 m/min. The results also showed tensile stress to be dominant, while compressive stress only occurred at v_c = 300 m/min for wall thicknesses of t = 1.5 mm and t = 2 mm. The developed response surface quadratic models make it possible to predict the tested variables under similar conditions. Full article

The application of 7050 aluminum alloy in high-friction environments is limited due to its insufficient surface wear resistance. This study aims to enhance its wear resistance by depositing Cr/(Zr,Cr)N/(Zr,Cr,Al)N multilayer composite coatings using filtered cathodic vacuum arc deposition (FCVAD) technology under different Cr cathode arc currents (65A, 85A, 105A, 125A). Coatings were characterized by SEM, EDS, XRD, nanoindentation, and reciprocating wear testing. Results show that increasing arc current from 65 A to 125 A led to grain coarsening, reduced Zr content, and increased Cr-rich microdroplets. Nanoindentation results indicated that the coating prepared under a 65 A current exhibited the best hardness (13.03 GPa) and elastic modulus (242.87 GPa), which is mainly attributed to the formation of fine grains and fewer surface defects under low current conditions. Reciprocating wear tests showed that the wear resistance of all coating samples was superior to that of the uncoated 7050 aluminum alloy substrate. At an arc current of 85 A, the best wear resistance was observed, combining a low wear rate (5.31 × 10⁻⁵ mm³) with good mechanical strength (hardness of 8.54 GPa). This study revealed the regulatory mechanism of Cr cathode arc current on the microstructure and performance of Cr/(Zr,Cr)N/(Zr,Cr,Al)N multi-layer composite coatings, providing a theoretical basis and experimental support for optimizing coating process parameters to enhance the wear resistance of aluminum alloy surfaces. Full article

Al7050 aluminum alloy substrates were coated with Cr, Ti, and Ti/Cr multilayer films via direct current magnetron sputtering to enhance their corrosion resistance. A comprehensive analysis, employing SEM and XRD, characterized the coatings’ morphology and composition, while electrochemical experiments assessed their corrosion performance. The Cr coating, despite exhibiting the largest thickness (588 nm), revealed a porous microstructure with inherent structural weaknesses. Conversely, the Ti coating, while possessing a dense structure, presented a significantly reduced thickness (96 nm). The Ti/Cr multilayer coating, with a thickness of 242 nm, achieved an optimal balance between structural density and overall thickness. Critically, the layered architecture of the Ti/Cr multilayer coating effectively impeded crack propagation and facilitated the formation of tortuous corrosion pathways. This intricate pathway morphology significantly hindered the diffusion of the corrosive medium, resulting in a notably low corrosion current density of 3.83 × 10⁻⁷ A·cm⁻². Comparative analysis revealed that the corrosion current density of the Ti/Cr multilayer coating was substantially lower than that of both the Cr and Ti coatings, demonstrating improvements of 2386% and 222%, respectively. These findings underscore the pivotal role of the multilayer structure in augmenting the corrosion resistance of aluminum alloys by providing a superior barrier to corrosive medium. Full article

Cr/Ti bilayer coatings were deposited on 7050 aluminum alloy via magnetron sputtering at substrate temperatures of room temperature (RT), 150 °C, and 300 °C to investigate temperature effects on microstructure, hardness, and corrosion resistance. All coatings exhibited Cr(110) and Ti(002) phases. Temperature significantly modulated corrosion resistance by altering pore density, grain boundary density, and passivation film composition. Increasing temperature from RT to 150 °C raised corrosion rates primarily due to increased pore density. Further increasing to 300 °C reduced corrosion rates mainly through decreased grain boundary density, while passivation film composition changes altered electrochemical reaction kinetics. Substrate-coating interface defect density primarily influenced hardness with minimal effect on corrosion. Consequently, the RT-deposited coating, despite lower hardness, demonstrated optimal corrosion resistance: polarization resistance (7.17 × 10⁴ Ω·cm²), charge transfer resistance (12,400 Ω·cm²), and corrosion current density (2.47 × 10⁻⁷ A/cm²), the latter being two orders of magnitude lower than the substrate. Full article

Nanostructured multilayer anticorrosion coatings offer an effective strategy to mitigate the poor corrosion resistance of aluminum alloys and extend their service life. In this study, four types of Ti/Cr multilayer coatings with varied modulation periods along the growth direction were deposited on 7050 aluminum alloy substrates using direct current magnetron sputtering. The cross-sectional microstructure of the coatings was characterized by scanning electron microscopy (SEM), while their mechanical and corrosion properties were systematically evaluated through nanoindentation and electrochemical measurements. The influence of modulation period distribution on the corrosion resistance of Ti/Cr multilayers was thoroughly investigated. The results show that the average thickness of the Ti/Cr multilayer coatings is 680 nm, the structure is dense, and the coarse columnar crystals are not seen. All Ti/Cr multilayer coatings significantly reduced the corrosion current density of 7050 aluminum alloy by about 10 times compared with that of the substrate, showing good protective effect. Modulation period along the coating growth direction decreases the Ti/Cr multilayer coating surface heterogeneous interface density increases, inhibits the formation of corrosion channels, hindering the penetration of corrosive media, and the other three coatings and aluminum alloy compared to its corrosion surface did not see obvious pore corrosion, showing the most excellent corrosion resistance. Full article

Limited hardness and corrosion resistance restrict 7050 aluminum alloys in aggressive environments. Cr coatings, applied as single layers or over Ti, Al, or Ni buffer layers, were deposited onto 7050 aluminum alloy by direct-current magnetron sputtering; their microstructure, adhesion, mechanical properties, and corrosion behavior were examined. The results indicate that introducing a buffer layer significantly enhances the bonding strength between a Cr coating and an aluminum alloy substrate, with the Ni buffer layer exhibiting the highest bonding strength, nearly three times that of the Cr coating alone. Furthermore, the buffer layer influences the mechanical properties of the Cr coatings, with Ni/Cr and Al/Cr coatings demonstrating increased hardness and elastic modulus. The Ni/Cr coating achieved the highest values of 3.95 GPa and 62.09 GPa, respectively. Regarding corrosion performance, The Cr coatings containing buffer layers showed markedly better corrosion resistance than the bare 7050 Al alloy. A compact Cr₂O₃ passive film formed on their surfaces, cutting the corrosion current density by roughly two orders of magnitude. Among all samples, the Ti/Cr coating performed best, registering the lowest current density (1.687 × 10⁻⁶ A cm⁻²) and the highest charge-transfer resistance (6090 Ω cm²). Full article

The direct-chill (DC) casting of diameter of 300 mm 7050 aluminum alloy ingots under the impact of intense melt shearing and electromagnetic fields (combined fields) was simulated using the COMSOL software 6.2 to determine the temperature distribution and melt flow. The results indicated that the use of electromagnetic fields, intense melt shearing, and combined fields can all improve melt flow velocity, heat transfer efficiency, temperature field uniformity, and reduce sump depth when compared to conventional DC casting. However, the use of combined fields creates the shallowest sump and the most uniform temperature field. With the application of electromagnetic field, intensive melt shearing, and combined fields, the sump depth was decreased from 121 mm of DC casting to 118 mm, 112 mm, and 110 mm, respectively. Under the impact of the combined fields, the increase in the rotor rotation speed leads to the enhancement of overall flow velocity, the improvement of temperature distribution uniformity, and the reduction of melt temperature in the sump. The temperatures at reference points A and B dropped from 631.80 °C and 645.26 °C to 630.20 °C and 630.75 °C, respectively, as the rotor rotation speed increased from 1500 rpm to 6000 rpm. Additionally, the application of the combined fields resulted in a uniform microstructure distribution and notable grain refinement. Full article

In this paper, regression and re-aging treatment (RRA) was performed on the 7050 alloy, and the evolution in the microstructure of the 7050 alloy was observed by metallography and SEM. The effect of regression and re-aging treatment on the hardness of the alloy was investigated; the maximum hardness was 84.576 HRB at 180 °C/30 min. It was found that with the increase in regression treatment time, the size of the precipitates on the grain boundaries gradually increased, while the number of the precipitates inside the grain decreased accordingly. In the course of the experiment, the η’ (MgZn₂) transforms into the η (MgZn₂). As a result, the hardness of the alloy showed a decreasing trend. Meanwhile, the precipitates on the grain boundaries gradually increased in size, while the number of precipitates within the grain boundaries correspondingly decreased. These results reveal the influence of the re-aging treatment on the microstructure and mechanical properties of 7050 aluminum alloy, providing an important experimental basis for further optimizing the performance of the alloy. Full article

Improving the surface quality and controlling the microstructure evolution of difficult-to-cut materials are always challenges in high-speed machining (HSM). In this paper, surface topography, defects and roughness are assessed to characterize the surface features of 7050 aluminum alloy (Al 7050) under HSM conditions characterized by high temperature, strain and strain rate. Based on multi-physical field coupling, the mechanism of microstructure evolution of Al 7050 is investigated in HSM. The results indicate that the surface morphology and roughness of Al7050 during HSM are optimal at f_z = 0.025 mm/z, and the formation of surface defects (adherent chips, cavities, microcracks, material compression and tearing) in HSM is mainly affected by thermo-mechanical coupling. Significant differences are observed in the microstructure of different machined subsurfaces by electron backscatter diffraction (EBSD) technology, and high cutting speeds and high feed rates contributed to recrystallization. The crystallographic texture types on machined subsurface are mainly {110}<112> Brass texture, {001}<100> Cube texture, {123}<634> S texture and {124}<112> R texture, and the crystallographic texture type and intensity are significantly affected by multi-physical field coupling. The elastic–plastic deformation and microstructural evolution of Al7050 alloy during the HSM process are mainly influenced by the coupling effects of multiple physical fields (stress–strain field and thermo-mechanical coupling field). This study reveals the internal mechanism of multi-physical field coupling in HSM and provides valuable enlightenment for the control of microstructure evolution of difficult-to-cut materials in HSM. Full article

Aluminum alloy 7050-T74 with varying zinc-to-magnesium (Zn/Mg) mass fractions was synthesized using melt casting and hot extrusion techniques. This study investigated the influence of different Zn/Mg ratios on the microstructure, mechanical properties, and corrosion resistance of the alloy. Light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing, and corrosion testing were employed as analytical methods. The findings indicate that as the Zn/Mg ratio increases from 2.36 to 3.84, the proportion of low-angle boundaries (LABs) within the alloys initially rises and then decreases, achieving a balance between high strength and favorable elongation. Specifically, at a Zn/Mg ratio of 2.72, the alloy exhibits a tensile strength of 641 MPa, a yield strength of 609 MPa, and an elongation of 10.1%. Additionally, increasing the Zn/Mg ratio to 2.90 slightly reduces intergranular corrosion resistance while enhancing exfoliation corrosion resistance. Full article

In order to study the feasibility of forming microtexture at the surface of 7050 aluminum alloy by laser-induced cavitation bubble, and how the density of microtexture influences its tribological properties, the evolution of the cavitation bubble was captured by a high-speed camera, and the underwater acoustic signal of evolution was collected by a fiber optic hydrophone system. This combined approach was used to study the effect of the cavitation bubble on 7050 aluminum alloy. The surface morphology of the microtexture was analyzed by a confocal microscope, and the tribological properties of the microtexture were analyzed by a friction testing machine. Then the feasibility of the preparation process was verified and the optimal density was obtained. The study shows that the microtexture on the surface of a sample is formed by the combined results of the plasma shock wave and the collapse shock wave. When the density of microtexture is less than or equal to 19.63%, the diameters of the micropits range from 478 μm to 578 μm, and the depths of the micropits range from 13.56 μm to 18.25 μm. This shows that the laser-induced cavitation bubble is able to form repeatable microtexture. The friction coefficient of the sample with microtexture is lower than that of the untextured sample, with an average friction coefficient of 0.16. This indicates that the microtexture formed by laser-induced cavitation bubble has a good lubrication effect. The sample with a density of 19.63% is uniform and smooth, having the minimum friction coefficient, with an average friction coefficient of 0.14. This paper provides a new approach for microtexture processing of metal materials. Full article

To investigate the feasibility and formation laws of fabricating micro-dimples induced by near-wall laser-induced cavitation bubble (LICB) on 7050 aluminum alloy. A high-speed camera and a fiber-optic hydrophone system were used to capture pulsation evolution images and acoustic signals of LICB. Meanwhile, a three-dimensional profilometer was employed to examine the contour morphology of the surface micro-dimple on the specimen. The results show that at an energy level of 500 mJ, the total pulsation period for the empty bubble is 795 μs, with individual pulsation periods of 412.5 μs, 217 μs, and 165 μs for the first, second, and third cycles, respectively, with most energy of the laser and bubble being consumed during the first evolution period. Under the synergy of the plasma shock wave and collapse shock wave, a spherical dimple with a diameter of 450 μm is formed on the sample surface with copper foil as the absorption layer. A model of micro-dimple formed by LICB impact is established. As the energy increases, the depth of the surface micro-dimple peaks at an energy of 400 mJ and then decreases. The depth of the surface micro-dimple increases with the increase in the number of impacts; the optimal technology parameters for the micro-dimple formation by LICB impact are as follows: the absorption layer is copper foil, the energy is 400 mJ, and the number of impacts is three. Full article