Search Results (86)

We simulate the dispersoid distribution within the Al matrix grains of an aluminum 6082 alloy by combining finite difference cell modeling with mean-field precipitation simulations. The results demonstrate that the initial as-cast microstructure and the heating rate during the ramp-up to the isothermal homogenization temperature are the most important factors governing the dispersoid particle distribution. The simulation results are validated by Electron Probe Microanalysis (EPMA) and Optical Microscopy on experimental run products. The results indicate that dispersoids can only achieve uniform distribution throughout the grain when the heating rate to the homogenization temperature is sufficiently slow. Full article

Understanding the development of an asphalt binder’s internal network structure is essential when interacting asphalt and crumb rubber. Thus, the focus of this study was to reveal the development of asphalt–rubber binders’ (A-RBs) network structures at different interaction times and their correlation with performance. Atomic force microscopy (AFM) was utilized to image the morphologies of the binders, and the binders’ performances were explored rheologically with a dynamic shear rheometer. Extending the interaction time to 8 h and utilizing a soft binder altered the network structures from agglomerated dispersoids—minuscule distributed phase zones embedded in the continuous matrix of the asphalt binder—to well-organized lamellar structures. At 8 h, using a softer binder increased stiffness by 25% and elasticity by 15%, accelerating early rubber dissolution. Extending the interaction time from 4 to 8 h increased rubber dissolution by 5–23%, depending on the binder type. The 150% increase in stress overshoot for A-RBs with the soft binder versus those with the stiff one reflects the development of the network structure. At 8 h, the soft binder reduced the AFM mean phase angle by 10% and the standard deviation by 64%, indicating a more homogeneous and stable network than that obtained with the stiff binder. Thus, the 8 h interaction time and soft binder facilitated rubber swelling and enhanced component diffusion, aiding in the formation of a homogeneous network. Full article

There is a demand for a 6005A series extrusion alloy with improved strength that maintains good extrudability. Replacing Mn and Cr dispersoid formers with Sc and Zr is expected to increase the room temperature mechanical properties while not affecting extrudability. Al₃X dispersoids with a Sc core surrounded by a Zr shell are stable at higher temperatures and enhance recrystallization resistance and precipitation strengthening. However, there is little information on how the Sc and Zr additions affect the properties of an extrudate as a function of extrusion geometry and ratio. A 6005A series alloy with Cr and Mn additions is compared to an alloy with Sc and Zr additions with rod and flat cross-sections at extrusion ratios of 25 and 92. The results show that Sc and Zr additions increased yield strength and ultimate tensile strength while maintaining ductility compared to Cr and Mn additions. Rod shapes performed significantly better than flat shapes, but there was no significant effect of extrusion ratio. Full article

Application of rare earths (RE) as grain refiners is well-known in the technology of aluminum alloys for the automotive industry. In the current study, Al-2.4%Cu-0.4%Mg alloy (coded 220) and Al-7.5%Si-0.35%Mg alloy (coded 356.1), were prepared by melting each alloy in a resistance furnace. Strontium (Sr) was used as a modifier, while titanium boride (TiB₂) was added as a grain refiner. Measured amounts of Ce and La were added to both alloys (max. 1 wt.%). The alloy melts were poured in a preheated metallic mold. The main part of the study was conducted on tensile testing at room temperature. The results show that although RE would cause grain refining to be about 30–40% through the constitutional undercooling mechanism, grain refining with TiB₂ would lead to approximately 90% refining (heterogenous nucleation mechanism). The addition of high purity Ce or La (99.9% purity) has no modification effect regardless of the alloy composition or the concentration of RE. Depending on the alloy ductility, the addition of 0.2 wt.%RE has a hardening effect that causes precipitation of RE in the form of dispersoids (300–700 nm). However, this increase vanishes with the decrease in alloy ductility, i.e., with T6 treatment, due to intensive precipitation of ultra-fine coherent Mg₂Si-phase particles. There is no definite distinction in the behavior of Ce or La in terms of their high affinity to interact with other transition elements in the matrix, particularly Ti, Fe, Cu, and Sr. When the melt was properly degassed using high-purity argon and filtered using a 20 ppi ceramic foam filter, prior to pouring the liquid metal into the mold sprue, no measurable number of RE oxides was observed. In conclusion, the application of RE to aluminum castings would only lead to formation of a significant volume fraction of brittle intermetallics. In Ti-free alloys, identification of Ce- or La-intermetallics is doubtful due to the fairly thin thickness of the precipitated platelets (about 1 µm) and the possibility that most of the reported Al, Si, and other elements make the reported values for RE rather ambiguous. Full article

This study investigates the effects of nano-oxide dispersoids on microstructural evolution, phase formation, and mechanical properties of W-Mo-Ti alloys reinforced with AlCoCrFeNi_2.1 during mechanical alloying. An EBSD/EDS analysis confirmed the formation of different phases, including the tungsten matrix, FCC reinforcement phase, Al₂O₃, and (Al,Cr) oxide. Y₂O₃ particles played a crucial role in refining the microstructure, promoting a uniform dispersion of the reinforcement phase and oxide particles in the tungsten model alloys. Mechanical testing demonstrates that the Y₂O₃-containing alloy exhibits improved hardness with prolonged milling, attributed to the refinement in the microstructure. In contrast, the Y₂O₃-free alloy shows reduced hardness due to the agglomeration of reinforcement phases surrounded by an (Al,Cr) oxide layer. The model tungsten alloys exhibit brittle behavior in compression tests, which can be attributed to the presence of (Al,Cr) oxide layers weakening the interfacial bonding and limiting plastic deformation. Full article

The long-term corrosion resistance of commercially pure aluminum (AA1050) processed by equal channel angular pressing (ECAP) was evaluated in a saline environment. The study compared the microstructure and corrosion behavior of ECAP-processed samples in route A with 1X, 4X, and 8X passes to an annealed sample using a 3.5% NaCl solution. Characterization techniques, including optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS), were employed. Results indicate that ECAP processing enhances the passive corrosion resistance compared to the undeformed sample. However, the improvement in corrosion resistance did not consistently increase with the number of ECAP passes. Factors such as the distribution of high- and low-angle grain boundaries, dislocation density, and fragmentation and redistribution of coarse dispersoid particles play a significant role in the corrosion behavior post-ECAP. Additionally, findings suggest that long-term immersion tests are required to obtain a more reliable electrochemical response. Full article

This study examined the effects of heat treatment on the microstructure and dynamic deformation characteristics of AA2519 aluminum alloy in T4, T6, and T8 tempers under high strain rates of 1000–4000 s⁻¹. A Split Hopkinson pressure bar (SHPB) was utilized to characterize the mechanical response, and microstructural analysis was performed to examine the material’s microstructure. The findings indicated varied deformation across all three temper conditions. The dynamic behavior of each temper is influenced by its strength properties, which are determined by the aging type and the subsequent transformation of strengthening precipitates, along with the initial microstructure. At a strain rate of 1500 s⁻¹, AA2519-T6 demonstrated a peak dynamic yield strength of 509 MPa and a flow stress of 667 MPa. These values are comparable to those recorded for AA2519-T8 at a strain rate of 3500 s⁻¹. AA2519-T4 exhibited the lowest strength and flow stress characteristics. The T6 temper demonstrated initial stress collapse, dynamic strain aging, and an increased tendency for shear band formation and fracture within the defined strain rate range. The strain rates all showed similar trends in terms of strain hardening rate. The damage evolution of the alloy primarily involved the nucleation, shearing, and cracking of dispersoid particles. Full article

This study presents the results of research on the influence of different contents of copper in aluminium alloys based on the 6xxx series on mechanical and structural properties. The investigation started with the alloying, and casting four billet variants with different copper content—0.8% Cu; 2B—1% Cu; 3A—1.2% Cu; and 3B—1.4% Cu. The prepared materials were homogenised and extruded on a 500T horizontal press with two different process temperatures and ram speeds ranging from 1 mm/s to 9 mm/s. After heat treating to the T6 and T5 tempers, their mechanical properties were tested. On this basis, the two most promising alloys 2A and 3B were selected and subjected to further tests. After extrusion and heat treatment of the profiles (to F, T1, T2, T5, and T5510), their mechanical properties were determined to select the preferred process parameters. Finally, a structural test based on crystallographic orientation based on the EBSD technique and TEM observations allowed for the characterisation of grain size, dispersoids, and phase analysis. Bright-field (BF) analysis allowed us to compare the deformed areas for T1, T5, and T5510 temperatures. The results showed significant growth in the mechanical properties of all the subjected alloys, and the best properties were shown for a Cu content of 1.4% with a tensile strength of 460 MPa and an elongation of 16% (T5510 tempering). The structural test showed an average grain size of 18 µm to 23 µm and solid solution decomposition differences for different heat-treating parameters. Full article

The impact of annealing on the recrystallized grain structure and superplastic behavior of two Al-Mg 5xxx alloys used for high-speed blow forming (HSBF) was studied. The results revealed that both alloys demonstrated rapid static recrystallization after only a few minutes of annealing at 520 °C, forming fine and equiaxed grain structures. After four min of annealing, Alloy 2 (Al-4.0Mg-1.18Mn) exhibited a higher fraction of small grains (<10 µm) compared to Alloy 1 (Al-4.5Mg-0.74Mn). Moreover, Alloy 2 displayed enhanced resistance to grain coarsening with increasing annealing times, which was attributed to its higher amount of Al₆(Mn,Fe) intermetallic particles and a higher number density of Mn dispersoids. Optimizing the annealing time can effectively develop a fine and stable grain structure in Al-Mg 5xxx alloys. During tensile deformation, Alloy 2 consistently showed higher ductility compared to Alloy 1 at low strain rates (170% vs. 138% at 0.001 s⁻¹ and 163% vs. 134% at 0.01 s⁻¹), whereas at a high strain rate of 1 s⁻¹, both alloys displayed comparable tensile elongation. The high superplastic response of Alloy 2 at low strain rates renders it a superior superplastic alloy for HSBF applications. Full article

Al-Mg alloys are characterized by permanent solid solution hardening and can additionally be work-hardened. The high mechanical properties of Al-Mg alloys with above-standard Mg content obtained after plastic deformation processes decrease over time. The addition of minor alloying elements like Er or Zr is an alternative method to improve the durability of mechanical properties and increase the strength of Al-Mg alloys due to densely and evenly distributed dispersoids being formed. In this paper, Al-Mg alloys with above-standard Mg content (7 wt.%) and Zr and Er micro-alloying elements and their influence on the microstructure and durability of the mechanical properties were examined. The cast ingots of AlMg7 alloys were characterized by a smooth surface without cracks. The plastic deformation process in a static compression test resulted in an about 60 HBW increase in the Brinell hardness of all the deformed alloys relative to casting. It was revealed that the addition of Er and Zr significantly improved the mechanical properties and durability of the mechanical properties of the Al-Mg after annealing. The addition of Er or Zr slightly restrained the decrease in the Brinell hardness after annealing but did not inhibit it. Full article

The friction stir welding (FSW) process is a unique combination of deformation and high temperature, which provides opportunities to modify microstructures through the adjustment of the processing parameters and is an ideal way to join non-weldable aluminum alloys by avoiding the formation of a molten pool. The 7xxx series heat-treatable aluminum alloys are widely used in the aerospace field as high-performance structural materials. The microstructure evolution and mechanical performance of these alloys are affected by the effects of thermomechanical processing, which provides opportunities to optimize the material properties by controlling microstructural features such as intermetallic constituent particles, dispersoids and nanoscale precipitates. This paper focuses on the basic principles of the thermal and mechanical effects generated during FSW on the evolution of second-phase particles in different zones of the weld. Full article

Before artificial ageing, extruded aluminium profiles are subjected to stretching with a small cold deformation in the range of 0.5–2%. This deformation improves the geometrical stability of the extruded product and causes changes in the microstructure of the profile, which leads to the strain hardening of the material after artificial ageing. The work has resulted in the creation of the prototype of an original device, which is unique in the world, for the dynamic stretching of the extruded profiles after quenching. The semi-industrial unit is equipped with a hydraulic system for stretching and a pneumatic system for cold dynamic deformation. The aim of this research paper is to produce advantageous microstructural changes and increase the strength properties of the extruded material. The solution of the dynamic stretching of the profiles after extrusion is a great challenge and an innovation not yet practised. The paper presents the results of microstructural and mechanical investigations carried out on extruded AlMgSi(Cu) alloys quenched on the run-out table of the press, dynamically stretched under different conditions, and artificially aged for T5 temper. Different stretching conditions were applied: a static deformation of 0.5% at a speed of 0.02 m/s, and dynamic deformation of 0.25%, 0.5%, 1%, and 1.5% at speeds of 0.05 and 2 m/s. After the thermomechanical treatment of the profiles, microstructural observations were carried out using an optical microscope (OM) and a scanning electron microscope (SEM). A tensile test was also carried out on the specimens stretched under different conditions. In all the cases, the dynamically stretched profiles showed higher strength properties, especially those deformed at a higher speed of 2 m/s, where the increase in UTS was observed in the range of 7–18% compared to the classical (static) stretching. The microstructure of the dynamically stretched profiles is more homogeneous with a high proportion of fine dispersoids. Full article

The effects of chromium (Cr) addition ranging 0.1–0.3 wt.% on the microstructure and mechanical properties of Al–7Si–4Cu–0.25Mg (wt.%) alloy have been investigated. The cast Cr-free alloy consisted of α-Al, eutectic Si, Q-Al₅Mg₈Cu₂Si₆ and θ-Al₂Cu phases. Doping of Cr resulted in the appearance of a polyhedron-shaped α-Al₁₃Cr₄Si₄ phase with a cubic structure. The Al₁₃Cr₄Si₄ particles were found to embed with Al₂Cu blocks and bring about size reduction for the Al₂Cu blocks. The area fraction of Al₁₃Cr₄Si₄ monotonously increased with Cr content. After T6 treatment, the Al₂Cu blocks almost fully dissolved and transformed to θ’-Al₂Cu precipitates in the Cr-containing alloys. TEM observation revealed relatively large-sized θ’ precipitates attached to Al₁₃Cr₄Si₄ dispersoids. The Cr-containing alloys showed impressive mechanical properties, with the peak strength up to 452 MPa at room temperature. The ductility exhibited an increasing trend with Cr content, but the strength dropped dramatically when the Cr content reached 0.3 wt.%. It is suggested that the strength contribution from the Al₁₃Cr₄Si₄ phase is limited, especially at an elevated temperature. Full article

Diesel engines in heavy-duty vehicles are predicted to maintain a stable presence in the future due to the difficulty of electrifying heavy trucks, mine equipment, and railway cars. This trend encourages the effort to develop new aluminum alloy systems with improved performance at diesel engine conditions of elevated temperature and stress combinations to reduce vehicle weight and, consequently, CO₂ emissions. Aluminum alloys need to provide adequate creep resistance at ~300 °C and room-temperature tensile properties better than the current commercial aluminum alloys used for powertrain applications. The studies for improving creep resistance for aluminum casting alloys indicate that their high-temperature stability depends on the formation of high-density uniform dispersoids with low solid solubility and low diffusivity in aluminum. This review summarizes three generations of diesel engine aluminum alloys and focuses on recent work on the third-generation dispersoid-strengthened alloys. Additionally, new trends in developing creep resistance through the development of alloy systems other than Al-Si-based alloys, the optimization of manufacturing processes, and the use of thermal barrier coatings and composites are discussed. New progress on concepts regarding the thermal stability of rapidly solidified and nano-structured alloys and on creep-resistant alloy design via machine learning-based algorithms is also presented. Full article

This research investigates the heat treatment parameters of 6061-aluminum alloy to enhance its mechanical properties. The Taguchi design-of-experiments (DOE) method was employed to systematically examine the effects of solutionizing temperature, solutionizing time, aging temperature, and aging time on the tensile strength of the alloy. Mechanical testing suggested a major influence of solutionizing and aging temperatures on the ultimate tensile strength of the alloy. The samples subjected to a solutionizing temperature of 540 °C for 3 h, followed by aging at 170 °C for 18 h, exhibited the highest ultimate tensile strength (293.7 MPa). Conversely, the samples processed at the lowest levels of these parameters displayed the lowest ultimate tensile strength (193.7 MPa). Microstructural analysis confirmed the formation of equiaxed grains, strengthening precipitates, precipitate clusters, and β (Mg₂Si) precipitates alongside Fe-Al-Si dispersoids. Energy-dispersive X-ray spectroscopy (EDS) analysis detected the presence of elemental precursors of β phase (Al-Mg-Si) and dispersoid-forming elements (Al-Fe-Si). X-ray diffraction spectroscopy (XRD) analysis revealed the persistence of the β phase in the alloy, indicating its contribution to the improved mechanical properties, which are mainly obtained by aging precipitation phases. Fracture analysis showed a ductile fracture mechanism, and examining fractured samples supported the findings of enhanced tensile properties resulting from the adequate selection of heat treatment parameters. We employed ANOVA (analysis of variance) to analyze the DOE results, using a multiple regression model to express the ultimate tensile strength of the alloy in terms of the variables used in the design. This yielded an adjusted coefficient of determination of 89.75%, indicating a high level of explained variability in the test data for evaluating the model’s predictive capacity. Full article