Al Alloy Research Articles

Deposition behavior of the gas-atomized 7075Al and TiB2/7075Al composite powders during cold spraying

To fabricate high-quality coatings or components of high-strength 7075Al alloy by cold spraying, it is essential to understand the impact behavior and bonding mechanisms of the feedstock powder particles. For providing a general comparison, 7075Al powder and TiB2/7075Al composite powder (7075Al alloy matrix reinforced with in-situ formed and uniformly dispersed nano-TiB2 particles) produced by gas-atomization were used as feedstocks in the present study. Single particle impact tests combined with finite element analysis (FEA) were performed on the pure Al and 7075Al-T6 substrates under different process parameter sets. To provide a more realistic description, the real powder strength and plastic parameters obtained by single-particle compression tests were used as input data in the FEA model. The results show that the presence of nano-TiB2 particles has significant strengthening effects on the composite powder, thus resulting in different plastic deformation behavior upon impact compared to 7075Al powder. When the composite particles impacted the soft material (pure Al), the substrate experienced a high degree of deformation, which led to high deposition efficiency due to the embedding effect. Comparatively, the hard substrate (7075Al-T6) was less deformed, whereas the composite particle was highly deformed. Compared to the composite particle, the 7075Al particle presented a slightly higher plastic deformation and pronounced metal jets, which led to a lower critical impact velocity for successful bonding. Interestingly, a fracture was observed at the grain boundaries of both 7075Al and TiB2/7075Al composite particles in the case of a high gas temperature regime, which probably revealed that the high shock energy associated with high-velocity impact led to such intergranular fracture.

Influence of gaseous dielectrics on the wettability of Al-6061 alloy using dry μ-electrical discharge milling

Superhydrophobic surfaces are essential for applications such as self-cleaning and corrosion resistance. This study explores the fabrication of superhydrophobic surfaces on Al-6061 alloy using dry micro electrical discharge milling (μEDM milling) and investigates the effects of gaseous dielectrics on wettability under atmospheric conditions. Surfaces machined in an oxygen environment showed a surface area roughness (Sa) of 4.68 μm, 73.3 % higher than those machined in argon, attributed to enhanced metal oxide formation. Energy Dispersive X-ray Analysis (EDAX) indicated a significantly elevated O/Al atomic ratio of 0.80 for oxygen-machined samples, which was 73.9 % greater than argon-machined samples, suggesting the presence of hydrophilic compounds such as AlO(OH) and Al2O3. Additionally, X-ray Photoelectron Spectroscopy (XPS) revealed that Al2O3 peaks on oxygen-machined surfaces were broadened and shifted to higher binding energies, correlating with decreased contact angles and increased surface hydrophilicity. These results suggest that using oxygen as a dielectric in theelectrical discharge machining (EDM) process promotes oxide layer formation, resulting in hydrophilic characteristics, while machining in argon encourages organic adsorption and greater hydrophobicity. The findings of this research provide insights that can inform future efforts to tailor surface properties for advancements in aerospace, automotive, and biomedical engineering applications.

Waterborne superhydrophobic bio-epoxy coating on Al alloy for corrosion-resistant and self-cleaning applications

Aluminum (Al) and its alloys are important engineering materials in modern industry due to their numerous advantages and have been widely used in various fields, including aerospace, marine, civilian industries and so on. However, they are prone to corrosion and contamination under harsh environmental conditions, particularly in marine environment when exposed to salty water or moisture for a long time, which can adversely affect their aesthetic appearance and desired functionalities or even cause economic losses and serious accidents. To prevent or delay the corrosion, the hydrophilic nature of Al and its alloy surfaces can be transformed to be hydrophobic or superhydrophobic. In this study, we reported an environment-friendly waterborne superhydrophobic bio-epoxy coating (WSBC) without using volatile solvents. The coating is composed of bio-epoxy resin, nano silica, silane coupling agent as well as hydrophobic curing agent, and applied by spin method on Al alloy substrates. The surface morphology and roughness were characterized by a field emission scanning electron microscope (FESEM) and an atomic force microscope (AFM). The WSBC with 22.2 wt% nano silica loading without considering the solvent of DI water displays a water contact angle (CA) as high as 165.8 ± 3.3° and a sliding angle (SA) as low as 5.3 ± 2.5°. Electrochemical measurement results showed that the as-prepared WSBC has a significant shift from −1.160 V to −0.708 V in the corrosion potential (Ecorr) and 3 orders of magnitude decrease in the corrosion current density (Jcorr), indicating excellent corrosion resistance. The WSBC was further proven to function well after immersion in deionized (DI) water and common organic solvents including ethanol and acetone for 48 h, and weathering resistance test. In addition, the as-prepared WSBC also showed good self-cleaning performance. The developed coating is green and no harm to human health and environment. The facile and eco-friendly process is of great importance for many industrial applications which can provide an attractive way towards anti-wetting surfaces for corrosion protection and self-cleaning effect on a variety of engineering substrates.

Achieving springback-free age forming via dislocation-enhanced stress relaxation in Al alloy

Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming. The stress-relaxation ageing (SRA) behavior and mechanical properties of a commercial 2219 aluminum alloy largely pre-deformed (LPD) by 80% have been systematically investigated. The stress relaxation ratio of the LPD alloy reaches approximately 94% regardless of the initial stress (50-350 MPa) after ageing for 12 h at 140°C. This relaxation ratio is about 2.9 and 1.8 times that in the T4 tempered alloy (27.6% under 50 MPa and 31.5% under 150 MPa) and T3 tempered alloy (37.6% under 50 MPa and 51.2% under 150 MPa), respectively. The microstructures, comprised of GP zones/θ' precipitates plus dislocation tangles, and tensile properties in the stress-relaxation-aged LPD alloys remain basically invariant with different initial stresses, as is vital importance for property consistency at different locations of the formed part. Under the same SRA condition, the LPD alloy has an increase of 150-230 MPa in yield strength relative to T3/T4 tempered alloy and obtains a uniform elongation of about 8%. A simple dislocation-based constitutive model accurately describing stress relaxation enhanced by the high dislocation density is established and embedded in the finite element package through a user subroutine. Simulations and experimental verifications show the LPD alloy sheet parts exhibit a nearly zero springback (< 5%) after unloading in contrast to the springback larger than 65% in the T3/T4 alloy sheet parts under the same condition. Our findings demonstrate the high-dislocation-density-enhanced SRA response enables a high-performance springback-free age forming of Al alloy sheet.

Arc characteristic in aluminum alloy double-wire variable polarity double base pulsed gas metal arc welding

The aluminum (Al) alloy double-wire pulsed gas metal arc welding (GMAW) has severe double arc interference issues. To reduce double arc interference, the advantages of double-wire pulsed GMAW and variable-polarity (VP) welding are combined to form Al alloy double-wire VP double base pulsed GMAW. The profile and behavioral characteristics of double arcs are analyzed using high-speed images to assess their physical properties. The arc load characteristics are explored through U-I curves, and the polarity switching process is analyzed from the perspective of double arc coupling. The experimental results showed that arcs with identical polarity are attracted to each other, while arcs with the opposite polarity repel each other. The coupling areas of two arcs with different polarities are therefore different; the electrode positive (EP) arc has a broader profile, while the electrode negative (EN) arc has an elongated profile. The stability of the leading arc is also affected by the polarity switching of the trailing arc. During the EN phase, the trailing arc can climb up to 2–3 times the wire diameter along the wire to search for metal oxide. The EN arc is more stable than the EP arc, and the EN peak arc has a load impedance that is 0.4–0.6 times lower than that of the EP peak arc. The polarity switching from EP to EN is easier due to the larger arc coupling area while switching from EN to EP is more difficult because of the thin arc coupling area. Regardless of polarity, the arc coupling area can provide charged particles for the arc to a certain extent and reduce the probability of arc extinguishing due to polarity switching.

Study on the Microstructure and Properties of Al Alloy/Steel CMT Welding–Brazing Joints Under Different Pulse Magnetic Field Intensities

Butt welding experiments on 6061 Al alloy and Q235B steel of 2 mm thickness were conducted using an ER4047F flux-cored wire as the filler metal, after adding a pulsed magnetic field into the process of cold metal transfer (CMT) welding. The effect of the pulsed magnetic field intensity on the macro morphology, microstructure, tensile strength and corrosion resistance of the welding–brazing joint was analyzed. The results showed that when the pulsed magnetic field intensity increased from 0 to 60 mT, the wettability and spreadability of the liquid metal were improved. As a result, the appearance of the Al alloy/steel joint was nice. However, when the pulsed magnetic field intensity was 80 mT, the stability of the arc and the forming quality of the joint decreased, which resulted in a deterioration in the appearance of the joint. A pulsed magnetic field with different intensities did not alter the microstructure of the joint. All of the joint was composed of θ-Fe2(Al,Si)5 and τ5-Al7.2Fe1.8Si at the interface and Al-Si eutectic phase and α-Al solid solution at the weld seam zone. Actually, with the pulsed magnetic field intensity increasing from 0 mT to 60 mT, the IMC thickness in the interfacial layer gradually reduced under the action of electromagnetic stirring. Also, the grain in the weld seam was refined, and elements were distributed uniformly. But when the pulsed magnetic field intensity was 80 mT, the grain in the weld seam began to coarsen, and the intermetallic compound (IMC) thickness was too small, which was unfavorable for the metallurgical bonding of Al alloy and steel. Therefore, with the increase in pulsed magnetic field intensity, the tensile strength of the joints first increased and then decreased, and it reached its maximum of 187.7 MPa with a pulsed magnetic field intensity of 60 mT. Similarly, the corrosion resistance of the joint first increased and then decreased, and it was best when the pulse magnetic field intensity was 60 mT. The Nyquist plot and Bode plot confirmed this result. The addition of a pulsed magnetic field caused less fluctuation in the anode current density, resulting in less localized corrosion of the joint using the scanning vibrating electrode technique (SVET). The XPS analysis showed the Al-Fe-Si compounds replacing the Fe-Al compounds in the joint was the main reason for improving its corrosion resistance under the action of a pulsed magnetic field.

Current waveform effects on AC-CMT arc welding of 7075 Al alloy with addition of ER7075 wire

Current waveform effects on AC-CMT arc welding of 7075 Al alloy with addition of ER7075 wire

Strong and thermally stable nanocrystalline Cu–Al alloy via Al segregation

Strong and thermally stable nanocrystalline Cu–Al alloy via Al segregation

Hot Deformation and Dynamic Recrystallization of 7075 Al Alloy in the Extruded State

Hot Deformation and Dynamic Recrystallization of 7075 Al Alloy in the Extruded State

Fatigue life of friction stir spot welds between Z91 magnesium alloy and ENAW7075-T651 aluminum alloy

Abstract Magnesium (Mg) and aluminum (Al) alloys are considered to be among the lightest structural metals. Using these materials in a design can considerably decrease weight, which brings many benefits like reducing fuel consumption and increasing the performance of an aircraft or a ground vehicle. However, these alloys are too difficult to be joined via fusion welding techniques. In this context, welding AZ91 Mg alloy to ENAW7075-T651 Al alloy by the solid-state welding method of friction stir spot welding was investigated comprehensively. These alloys were welded by utilizing a tool with a triangle pin and various tool rotational speeds (1,000, 1,400, and 1,800 rpm) and welding times (3 and 6 s). Macro and microstructure of the welds and their hardness, tensile strength, and tension-compression fatigue life were determined. Generally, an improvement in the mechanical properties of the weld was observed by increasing the welding time due to the expansion of the joining area. The welding with the best mechanical properties was obtained at 1,400 rpm, and the worst at 1,800 rpm. All the welds failed from the weld area during the tensile and fatigue tests and exhibited a brittle fracture mode due to the formation of intermetallic compounds in the welds.

Optimization of the Thickness Ratio and Roll-Bonding Parameters of Bimetallic Ti/Al Rod for Bending-Dominated Negative Thermal Expansion Metamaterials

Roll-bonding has rarely been applied to prepare rods for negative thermal expansion metamaterials (NTEMs). Parameters for quantitatively assessing the isotropy and cyclic thermal stability of the thermal expansion coefficient α of NTEMs are lacking. Here, the Ti-to-Al thickness ratio in bimetallic rods for “cross-shaped” node bending-dominated NTEMs was optimized using a general model proposed in the literature. The finite element method was used to determine the optimal initial thickness ratio of the billet, as well as the reduction ratio and rolling temperature. NTEMs were prepared with roll-bonded Ti/Al rods and Ti nodes. A relatively high thermal expansion coefficient was obtained when the thickness ratio of the 7075 Al alloy of the rods was in the range of 0.56–0.60. The optimized roll-bonding process to meet this thickness ratio was as follows: a rolling temperature of 400 °C, a reduction ratio of 50%, and TA1 Ti and 7075 Al billet thicknesses of 0.5 mm and 1.5 mm, respectively. The isotropy and cyclic thermal stability ratios were proposed to quantitatively assess the isotropy and cyclic thermal stability of the NTEMs. These results help to expand the preparation and evaluation methods for NTEMs.

Local stress/strain field analysis of die-casting Al alloys via 3D model simulation with realistic defect distribution and RVE modelling

The deformation and fracture behavior of die-casting aluminium (Al) alloys is very complex. Due to local variations in properties, the microstructure and mechanical behavior of materials are highly anisotropic. In this paper, an attempt has been made to quantitatively study the defect characteristics of high pressure cast Al alloy parts using experimental and finite element calculation methods, and to analysis the effect of local porosity and pore size on plasticity. Three-dimensional solids with real defect distribution are obtained by using 3D X-ray computed tomography, and used as an input for building a finite element model. The damage initiation of cast Al alloys under complex stress states is analyzed from micro to macro scales. Crack propagation occurs through two modes of microporous agglomeration: aggregated pores produce cracks from internal necking and stress concentration. Then, they expand in the same direction, agglomerate in a specific direction and eventually fracture. Subsequently, the effect of porosity on non-homogeneity was elucidated by obtaining local stress/strain behavior through digital image correlation measurements. Additionally, a theoretical framework of elasto-plastic deformation of microstructures and a 3D representative volume element model are developed to simulate the deformation and damage processes under cyclic boundary conditions of materials. The simulation results show that the local stress/strain around the pores evolves gradually with deformation. During the die casting process, the method demonstrates the ability to predict the mechanical behavior of Al alloys.

Dowel-like morphology of Cu2Al3 enhances shear strength of interfacial layers in Cu-Al composites

Developing bimetallic interfaces with high interfacial bonding strength is important for metallic composites used under harsh service conditions. However, the formation of brittle intermetallic compounds is unavoidable for some interface combinations, resulting in a significant deterioration of bonding strength. In this work, we demonstrate the development of a Cu alloy/Al alloy interface with a shear strength of 126±15 MPa – a value almost twice that reported in previous studies. The exceptional interfacial bonding strength is attributed to a special interface structure, composed of brittle intermetallic compound layers connected internally by dowels of a metastable Cu2Al3 phase, achieved via alloy design and process control. During solid-liquid composite processing, a liquid diffusion layer forms at the interface between the Cu and Al alloys. A precursor Cu4Al7Ni phase then develops at the Cu side and transforms into a metastable Cu2Al3 phase with a banded structure. Finally, layers of Cu9Al4 and CuAl2 layers form, which are fully connected to the Cu2Al3 phase. The banded arrangement of the Cu2Al3 phase acts to block crack propagation and deflect cracks into the eutectic layer and Al alloy, resulting in an ultra-high interfacial bonding strength. This work demonstrates that high interfacial bonding strength can be achieved by tailoring the interface structure instead of by decreasing the interface thickness, and thus paves a new way for developing high-performance bimetallic interfaces.

Highly reflective ZrC-Cu-based metal matrix composite coatings deposited via cold-spray for laser protection applications

Lasers are very powerful and can produce high temperatures, capable of melting materials when projected with an appropriate power, exposure time, distance, and beam width. High energy lasers are used for attacking enemy aircraft and missiles; however, the same threat is inevitable to the allied aircraft and missiles. Surface coatings have proven to be a viable solution to reduce damage from such laser attacks. In the present work, ZrC-Cu-based highly reflective coatings were deposited on Al-6061 alloy using the cold spray to develop laser damage resistance. Microstructural characterization, XRD, micro-hardness, reflectivity measurements, and laser ablation tests were conducted on the developed materials. The results showed improved ceramic retention and mechanical properties along with minimal porosity in the coating with increasing ZrC content in the feedstock. Additionally, the XRD analysis revealed that Cu-ZrC composite coatings could be produced by cold spray, without decarburisation of ZrC or oxidation of Cu. Owing to the exceptional purity in coatings, highly reflective coatings were obtained. At the target wavelength of 1080 nm, Cu-30 %ZrC composition achieved a remarkable reflectivity of 75 % (85 % of bulk copper). The coatings with compositions of Cu-30 %ZrC, Cu-50 %ZrC and Cu-70 %ZrC remained undamaged under laser irradiation, whereas Cu-85 %ZrC exhibited a laser ablation pit. These findings provide valuable insights into developing optimized ZrC-Cu coatings against laser irradiation.

Effect of Extrusion Ratio on Microstructure and Properties of Al-1.5Fe-0.4Cr Alloy Obtained by Continuous Rheo-Extrusion

Due to the shortage of primary Al resources and significant consumption of Al resources, recycled Al has become a focus of attention. In the process of recycling Al, the Fe element is the most hazardous impurity element, and the coarse Fe-containing phases lead to a reduction in the mechanical properties of recycled Al. In this work, an Al alloy with 1.5 wt% Fe and 0.4 wt% Cr was viewed as a recycled Al, approximately. The continuous rheo-extrusion technique was used to refine the Fe-containing phases in the Al-1.5Fe-0.4Cr alloy, improving the mechanical properties of the alloy. The effect of the extrusion ratio on the microstructure and properties of the continuous rheo-extrusion was investigated. The results showed that, when the extrusion ratio was changed from 4 to 5, the percentage of low-angle grain boundaries in the alloy increased from 45.5% to 53.1%, the average orientation angle reduced from 23.9° to 23.3°, and the grain size decreased from 4.3 ± 0.2 μm to 2.6 ± 0.1 μm. As a result, the ultimate tensile strength, yield strength and elongation of the alloy, with an extrusion ratio of 5, were 161.5 ± 2.8 MPa, 112.3 MPa ± 2.6, and 36.9% ± 1.6%, respectively. Grain refinement and Fe-containing phase refinement were responsible for the improvement in the mechanical properties of the alloy.

Enhancing intergranular corrosion resistance of 7055 Al alloy by ultrasonic shot peening

High strength 7000 series Al alloys are quite sensitive to intergranular corrosion (IGC) and generally a trade-off between IGC resistance and hardness exists in such Al alloys. Here, by using ultrasonic shot peening (USSP) we fabricate a gradient AA7055 whose IGC is significantly enhanced in both 57 g/L NaCl + 10 mL/L H2O2 solution and 3.5 wt% NaCl solution, whereas the surface hardness increases by 10 %. TEM microstructure characterization and nanoscale investigation of corrosion indicate that the improvement in IGC resistance can be attributed to the disappearance of grain boundary precipitates and precipitate free zones. Surface hardening mechanism is also revealed.

Corrosion Inhibition of PAAS/ZnO Complex Additive in Alkaline Al-Air Battery with SLM-Manufactured Anode

In order to improve the electrochemical activity and discharge performance of aluminum–air batteries and to reduce self-corrosion of the anode, an SLM-manufactured aluminum alloy was employed as the anode of the Al-air battery, and the influence of PAAS and ZnO inhibitors taken separately or together on the self-corrosion rate and discharge performance of the Al-air battery in a 4 M NaOH solution were investigated. The experimental result indicated that the effect of a composite corrosion inhibitor was stronger than that of a single corrosion inhibitor. The addition of the compound inhibitor not only promoted the activation of the anode but also formed a more stable composite protective film on the surface of the anode, which effectively slowed down the self-corrosion and improved the utilization rate of the anode. In NaOH/PAAS/ZnO electrolytes, the dissolution of the Al6061 alloy was mainly controlled by the diffusion of the electric charge in the corrosion products or the zinc salt deposition layer. Meanwhile, for the Al-air battery, the discharge voltage, specific capacity, and specific energy increased by 21.74%, 26.72%, and 54.20%, respectively. In addition, the inhibition mechanism of the composite corrosion inhibitor was also expounded. The excellent discharge performance was due to the addition of the composite corrosion inhibitor, which promoted the charge transfer of the anode reaction, improved the anode’s activity, and promoted the uniform corrosion of the anode. This study provides ideas for the application of aluminum–air batteries in the field of new energy.

Studies of SiC‐Filled Al6061 Metal Matrix Composite Optical, Mechanical, Tribological, and Corrosion Behavior with Strengthening Mechanisms

The objective of the current study is to produce metal matrix composites (MMCs) using ultrasonic‐assisted stir casting and Al6061 alloy reinforced with silicon carbide (SiC) microparticle reinforcement in weight percentages of 0, 2, 4, and 6. The microstructural alterations of Al6061–SiC composites are investigated using a scanning electron microscope (SEM) equipped with an energy‐dispersive X‐ray (EDAX). By adding more nucleation sites for the formation of smaller grains, SiC reinforcement of the Al6061 matrix encourages grain refining. The SiC addition significantly changes the microstructure of Al6061 composites, enhancing their mechanical qualities. In addition to increasing density by 0.6%, hardness by 33%, and tensile strength by 33%. The increased SiC content dramatically decreases elongation by 42%. The strength of Al6061–SiC MMCs is predicted using several strengthening mechanism concepts as part of the continuing investigation. For Al6061–SiC composites, the strengthening contribution from thermal mismatch is more significant than that from Orowan strengthening, Hall–Petch mechanism, and load transmitting effect. Grain refinement interactions, load transmission mechanisms, and the strengthening effects of CTE differences and dislocations between matrix and reinforcement particles are studied. The composite with 6‐weight percent SiC reinforcement performs better in dry sliding wear and corrosion resistance.

Exploring Ti-rich ternary Laves phase alloys for efficient hydrogen storage

Striking an optimal balance between the hydrogen storage properties and cost, while identifying a viable material capable of storing hydrogen under ambient conditions, remains a persistent challenge in the present era. AB2-type laves phase alloys have garnered significant interest due to their hydrogen storage capabilities. This work employs a strategy of utilizing inexpensive Ti to occupy either Ni or Al sites, to form Ti-rich alloys, with the aim of enhancing the hydrogen storage properties of Ti–Ni–Al alloys. We used the first-principles approach to systematically explore the structural, electronic, and hydrogen storage properties of Ti-rich ternary Laves-phase alloys. Accordingly, we investigated two Ti-rich alloys for their hydrogen storage capabilities: one with a fixed Al-composition, Ti5Ni3Al4, and the other with a fixed Ni-composition, Ti5Ni4Al3. Our investigation shows that the A2B2 tetrahedral site is the energetically stable site for the hydrogen absorption of these alloys. Specifically, Ti-rich, with fixed Ni-concentration (Ti5Ni4Al3), exhibits a higher hydrogen weight percentage than the fixed Al-concentration (Ti5Ni3Al4). Furthermore, we have included the release temperatures corresponding to the hydrogen concentration. With enhanced kinetics in Ti5Ni4Al3, we conclude that the release temperatures are within the working temperature range for fuel cell applications. Additionally, we have used a thermodynamical model to explore the pressure–composition–temperature (PCT) curves for AB2 type laves phase systems and provided a comparative analysis for the compounds under study. This study offers valuable insights for the development of cost-effective, Ti–Ni–Al hydrogen storage alloys with better hydrogen storage properties.

Development of ultra-high-strength Al-Mg-Si conductor alloys with copper addition via scalable thermomechanical processes

An ultra-high strength Al-Mg-Si conductor alloy was developed using the addition of 0.4 wt.% Cu. Using scalable thermomechanical processes, the Cu addition resulted in a substantial 37% increase in the ultimate tensile strength (UTS) with a slight 4.5% decrease in the electrical conductivity (EC), achieving 500 MPa UTS and 49% IACS EC. This breakthrough achievement holds promise for replacing the steel core traditionally used in aluminum conductor steel reinforced (ACSR) cables with high-performance Al alloys. The significant increase in the strength of the developed alloy was attributed to the formation of coherent Cu-containing β" precursors during preaging, which exhibited higher dissolution resistance during wire drawing, thereby remaining highly dispersed in the matrix after 92% area reduction.