Al Solid Solution Research Articles

Advancements in joining Al-Zn-TiC-Mg composites using friction stir welding process: Influence of traverse speed

In this article, dissimilar magnesium and aluminum alloys were welded with a Zn interlayer and TiC nanoparticles by friction stir welding. Optimal joining conditions were achieved by a combination of three traverse speeds (30, 45, and 60 mm/min) and constant rotational speeds (1050 rpm). The best microstructure evolution and mechanical properties were achieved for specimens joined at rotational and traverse speeds of 1050 rpm and 45 mm/min, respectively. The grain size decreases as the traverse speed increases from 30 to 45 mm/min due to a reduction in heat input, an improvement in reinforcing distribution, and high intermixing of materials, then increases from 45 to 60 mm/min due to inadequate heat input for recrystallization process. It was shown that the TiC particles play a prominent role in the microstructure modification and enhance mechanical properties of weld samples while the Zn foil interlayer plays a vital in avoiding the formation of Al-Mg IMC phases. The obtained result under optimal welding parameters indicates that MgZn2, Mg-Al-Zn compounds, Mg and Al solid solution, were the main detected common phases in the stir zone instead of the brittle and hard Al-Mg IMCs formation. The average hardness values of 232 Hv were achieved, while the strength of the weld specimen experiences the 189 MPa value. In addition, a combination of brittle and ductile modes was observed based on the fracture surface of the weld sample after the tensile test.

Simultaneously enhancing mechanical and anti-corrosion properties of aluminum through electrodeposition of supersaturated Al(Fe) solid solutions

The heterogeneous microstructure in bulk aluminum (Al) alloys or coatings, comprising an α-Al solid solution matrix and coarse intermetallic compounds (IMCs), poses a challenge in balancing mechanical and anti-corrosion properties. This challenge is particularly pronounced in Al alloys with high iron (Fe) content. Here, supersaturated Al(Fe) solid solutions with a single phase have been electrodeposited using imidazolium chloroaluminate ionic liquids (ILs). Ferrous chloride (FeCl2) dissolved in Lewis-acidic ILs is assumed to form Cl-bridged [Fe(AlCl4)4]2−, which, together with the well-known Al2Cl7− species, supports the reduction and deposition of Al(Fe) alloy coatings. The supersaturated Fe solutes significantly strengthens the Al matrix, with the hardness of Al(Fe, 6.6 at.%) reaching up to 3.43 GPa, surpassing that of any commercial Al alloys and other binary Al-based solid solutions. Moreover, the Al(Fe) deposits demonstrate superior anti-corrosion performance compared to pure Al. The homogeneous microstructure and extended Fe solubility within Al(Fe) solid solutions inherently contributes to a simultaneous improvements in mechanical and anti-corrosion properties. The nanograined and compact structure also benefit these properties. Accordingly, the combination of electrodeposition techniques and Al(Fe) alloys offers a promising approach for providing effective mechanical and chemical protection on metal surfaces.

Utilizing integrated neutron diffraction and elastoplastic self-consistent crystal plasticity model to quantitatively assess the strengthening mechanism in Al–12.5Ce and Al–12.5Ce–0.4Mg alloys

An integrated in-situ neutron diffraction and elastic plastic self-consistent crystal plasticity (EPSC-CP) modeling scheme is performed on a binary Al–12Ce alloy and a ternary Al–12Ce–0.4Mg alloys. Using this scheme, the constitutive parameters, i.e. elastic constants and slip system parameters of individual phases can be calibrated which can be used in microstructure-based CP models to predict materials performance. From this study, it is shown that the elastic constants of Al11Ce3 intermetallics calculated from density function theory calculation in the literature are rather accurate. When applied to the EPSC-CP model, the lattice strains of both the binary and ternary alloys are correctly predicted as compared with experiments, and large lattice strain differences between Al (100) plane and Al11Ce3 (010) plane are demonstrated. The slip system parameters calibrated by the scheme shows that the addition of 0.4 wt% Mg in the alloy has little influence on the critical resolved shear stress of initial dislocation glide in the Al matrix which caused plastic yield in the material. This can be explained by the very dilute Mg solute content in the Al solid solution, causing large spacing of Al–Mg lattice misfit sites and little impact on resistance of dislocation glide at initial yield. The 0.4 wt% Mg addition, on the other hand, has a large influence on the hardening term in the slip system parameters, indicating those Al–Mg misfit sites do help dislocation accumulation during the deformation. The impact of dilute Mg addition on the Al slip system parameters is also reflected in the flow behavior of the ternary alloy: little impact on the yield stress, but a large impact on working hardening and tensile strength of the materials which is consistent with the literature.

Effect of sintering temperature on microstructure and properties of Cu/graphite composites hybridized with MoAlB ceramic particles

Using a fast hot press sintering technique, Cu/graphite composites doped with MoAlB ceramic particles were synthesized. The impact of varying sintering temperatures on the composites' mechanical, tribological, and microstructure characteristics were studied. The Al element diffused from the MoAlB particles into the copper matrix and produced the MoB phase when the sintering temperature rose over 850 °C. The formation of MoB phase, which was well bound to the matrix, and the formation of Cu(Al) solid solution could improve the plastic deformation resistance of the composites. This, along with the lubrication supplied by graphite, synergistically improved the mechanical and frictional properties of Cu/graphite composites. The composites exhibited remarkable wear resistance (the wear rate was reduced to 3.36 × 10−5 mm3·N−1·m−1) and high compressive strength (266.25 MPa) when the sintering temperature was set to 900 °C. In order to create high-performance copper-based self-lubricating composites, this effort may offer a new research direction.

Interface energy, adhesion work and electronic structure of Ti3AlC2/Ag interface calculated from first principles

In this paper, based on the first-principles calculation of density functional theory, the adhesion work, interface energy and electronic structure of Ag/Ti3AlC2 interface are systematically studied. In the calculation process, 18 interface models with different terminals and different stacking sequences are considered. After comparing the calculation results, it is found that the interface model of Al terminal is the most stable among the six interface models of Ti1(C), Al, C(Ti2), Ti2(Al), C(Ti1) and Ti2(C). After changing the stacking order of Al terminal interface atoms, it can be found that the order of interface stability of Al terminal is HCP > FCC > OT according to the interface energy, and the interface energy of HCP interface model is 2.209J/m2. After the comprehensive analysis of adhesion work, interface energy and electronic structure, it is found that the theoretical calculation results are consistent with the previous experimental results. Al atoms have a tendency to move to the Ag matrix and form Ag (Al) solid solution, and the formation of solid solution further increases the stability of the interface.

Effect of cluster chemistry on the strengthening of Al alloys

When a supersaturated Al solid solution is held at room temperature, natural ageing occurs through the formation of clusters/zones providing a strengthening of the material. Recently, it was shown that this process can be greatly amplified by applying a cyclic plastic strain to a supersatured Al alloy. The cyclic strengthening also leads to a microstructure dominated by clusters/zones but the strengths are much higher than those obtained by natural aging, and can even exceed the peak aged strength.This work uses a combination of atom probe tomography and small angle x-ray scattering to provide a quantitative comparison of the cluster states in commercial Al alloys AA2024 and AA7075, after both natural aging and cyclic strengthening. We show that the chemistry of the clusters formed by these processes is different, and the clusters formed by cyclic strengthening tend to have chemistries closer to the composition of the relevant local equilibrium precipitate.The average force required to shear an individual cluster/zone is back-calculated from the strengthening observed experimentally and a strong correlation is found between the shearing force and the solute content of the cluster (i.e. 1-XAl, where XAl is the Al content of the cluster). This correlation applies not only for AA2024 and AA7075, but also AA6111 and AA7050 data taken from the literature, as well as some precipitates formed at elevated temperatures. This work shows that the first order effect controlling cluster strengthening is simply the cluster chemistry and its proportional effect on the force required to shear a cluster.

Synthesis and characterization of a new (Ti1-yCuy)2(Al1-xCux)C MAX phase solid solution

New [Ti(1-y)Cuy]2[Al(1-x)Cux]C solid solutions have been synthesized by solid-state reaction performed at 760 and 800 °C on compacted Ti2AlC-40 vol % Cu composite particles produced by mechanical milling. Using XRD and EDXS, it is demonstrated that Cu atoms can enter the crystallographic structure of the Ti2AlC MAX phase, whereas a Cu(Al) solid solution is formed during thermal treatment. A selective chemical etching of the Cu(Al) matrix is performed to determine the composition of the MAX phase solid solution by analyzing the filtrate and the solid phase using ICP-OES end EDXS methods respectively. (Ti0.85Cu0.15)2(Al0.75Cu0.25)C and (Ti0.85Cu0.15)2(Al0.58Cu0.42)C solid solutions are formed after thermal treatment at 760 and 800 °C, respectively. The substitution rate on the A site of the MAX phase thus increases with temperature.

Spark Plasma Sintering and Hot Pressing of Cu+Al Powder Mixtures and Pre-Deposited Cu/Al Layers

Reactive processing of metals is interesting for materials design and achieving new sets of properties. The transformation degree of the metals, the factor governing the properties of the material as a whole, depends on the sintering/heat treatment conditions. In the present investigation, the phase and microstructure formation of materials obtained by sintering of Cu-10 wt.% Al mixtures and layered Cu/Al structures under different modes of pressing/heating is presented. The samples were obtained via spark plasma sintering (SPS), hot pressing (HP) and pressureless sintering. The products of the interaction between the metals were Al2Cu and Cu9Al4 intermetallics and Cu(Al) solid solutions. The influence of the consolidation method on the phase composition of the sintered materials was studied. The hardness of the composites was analyzed in relation to their structural features. A model experiment has been conducted to trace the structural evolution at the Cu/Al interface caused by interdiffusion. The Cu/Al layered structures obtained by detonation spraying of the powders on a steel substrate were treated by SPS or HP. The effect of electric current, which is a feature of SPS processing, was in accelerating the reaction product formation in the layered structures still containing the starting metallic reactants.

Effect of Mechanical Alloying on the Dissolution of the Elemental Mn and Al-Mn Compound in Aluminum

The grain boundary, solid solution, and precipitation strengthening mechanisms are important for controlling the mechanical properties of Al-based alloys. Due to severe plastic deformation, mechanical alloying refines grain structure to a nanoscale level which leads to a strong increase in solute content and the related strengthening effect of solute atoms and secondary-phase precipitates. This study analyzed the elemental Mn and Al6Mn phase dissolution in Al during high-energy ball milling. For this purpose, XRD data, microstructure, and hardness evolutions were compared for two Al—5.2 at% Mn alloys prepared by mechanical alloying using elemental Al and Mn powders and a pre-melted master alloy. In the two-phase master alloy, containing the Al solid solution and the Al6Mn phase, the strain accumulation, grain refinement, solid solution supersaturation, and milling-induced hardening effects were facilitated. Both elemental Mn and intermetallic compound were dissolved during mechanical alloying, and the maximum solute content was near 3.1 at% Mn. A fine crystalline size of ~25 nm and the maximum Mn solute content were observed after milling of elemental powders and the master alloy for 60 h and 20 h, respectively. The microhardness of ~3 GPa corresponded to a ~3.1% solute Mn content, and the microhardness increased to ~5 GPa after long–term milling due to precipitation strengthening effect of the secondary Al6Mn phase in the master alloy.

Morphological and structural changes of sintered Cu-10 wt% Al materials with different alloying levels in salt spray environment

Morphological and structural changes of spark plasma sintered Cu-10 wt% Al materials in salt spray environment were studied. The tested materials possessed the same elemental composition but different phase compositions (Cu-Al composite, Cu(Al) solid solution and Cu-Cu(Al)-Cu9Al4 alloy). The oxide films formed on the surface of the corroded samples were confirmed to be enriched with Al. The subsurface regions of the Cu-Al composite and Cu(Al) solid solution did not reveal any microstructural changes after the salt spray test. When the Cu-Cu(Al)-Cu9Al4 alloy corroded, the aluminum contained in the alloy oxidized such that the oxide particles formed both on the surface of the sample and in the subsurface region. While the Cu-Al composite and Cu(Al) solid solution maintained integrity, the Cu-Cu(Al)-Cu9Al4 alloy experienced swelling and cracking during the salt spray test.

Structure and Electrical Properties of AlFe Matrix Composites with Graphene

Composites based on Al-Fe alloys and reinforced with three-layer graphene sheets were synthesized “in situ” under a layer of molten salts. Composites containing 0.12 wt.% graphene were subjected to severe plastic deformation via high-pressure torsion. SEM and TEM were used to study the morphological and size characteristics of the composite structure in the as-cast and deformed states. Herein, it is shown that severe plastic deformation leads to the deformation-induced dissolution of iron-containing aluminides with the formation of a supersaturated Al solid solution with a submicrocrystalline structure. The hardness and electrical properties of the graphene composites were measured in different structural states and compared to the characteristics of the matrix alloy.

Microstructural characterization of rapidly solidified Al-13.5 at.% Cr and Al-13.5 at.% V alloys for catalytic applications

Intermetallic compounds, due to their well-defined stoichiometry, arrangement of atoms and controlled crystal structure, are a promising alternative to expensive noble metal catalysts. In this paper, the catalytic properties of Al-13.5 at.% Cr and Al-13.5 at.% V alloys, corresponding to the quasicrystalline approximants Al45Cr7 and Al45V7, were investigated for the first time.The alloys in the form of fragmented brittle ribbons were produced by the melt-spinning. The microstructure of the ribbons, both in the as-spun state and after heat treatment (100 h at 600 °C), was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. In the as-spun state, the ribbons showed a multiphase microstructure. In addition to the Al45Cr7 phase in the Al-Cr alloy and the Al3V phase in the Al-V alloy, they also contained α(Al) solid solution and icosahedral quasicrystalline phases. After heat treatment, the alloys became almost single phase, consisting mainly of stable monoclinic phases: Al45Cr7 or Al45V7. The catalytic performance of the phenylacetylene hydrogenation reaction was tested on as-spun and heat-treated alloys that had previously been pulverized and sieved to select a powder fraction of less than 32 µm. All the tested materials show high substrate conversion, above 80% after 1 h reaction, along with high activity rate. The homogenized powders demonstrated a slightly better properties in relation to as-spun materials. These results confirm the potential of intermetallic catalysts, including the tested alloys, in hydrogenation reactions and verify the possibility of using the metallurgical method to obtain catalytically active materials.Graphical abstract

Crack-Free Copper Alloy Coating on Aluminum Alloy Fabricated by Laser Cladding

Crack-free Cu alloy coating has been fabricated on Al alloy substrate with the existence of a Ag buffer layer. The Cu alloy coating had 12 at.% Al and 45 at.% Ag, which contributed to the formation of Cu solid solution and the eutectic phase (transformation temperature 780 °C). The eutectic phase was characterized as finer Cu solid solution and finer Ag solid solution. The Ag buffer layer had the main contents of Ag2Al and Ag solid solution, and it not only hindered the formation of brittle intermetallic compounds (IMCs)but also reduced the thermal stress as its intermediate coefficient of thermal expansion (CTE). Furthermore, the plastic deformation of Ag solid solution in the Ag buffer layer and Cu solid solution in Cu alloy coating also relieved the thermal stress which was generated during the cladding process. All these three aspects inhibited crack generation. And the hardness of the Cu alloy coating increased to approximately 275 HV due to the strengthening effect of Al solid solution, grain boundary within the finer eutectic phase, and nano twin in the Cu solid solution of the eutectic phase.

Introducing both chemical and structural gradients in AISI 321 stainless steel via aluminizing and laser shock peening for superior properties

Aluminizing is a diffusion based chemical surface treatment on materials to provide excellent protection against high temperature oxidation and corrosion, but is likely to be accompanied by a degradation in mechanical properties. Laser shock peening (LSP) is a superior laser based surface strengthening technique for enhanced mechanical properties. In this study, we focus on combining these two methods on the AISI 321 stainless steel to introduce both chemical and structural gradients for superior properties. Comparative investigation on both the microstructure and mechanical properties of the as received 321 steel, aluminized 321 steel and the aluminizing + LSP processed steel indicated that: (1) A three-layer protective coating was introduced on the surface of the aluminized steel and the concentration of Al decreased gradually from the outermost layer to a certain depth, forming B2-FeAl(Cr) solid solution and Al2O3 in Layer-I, B2-FeAl and DO3-Fe3Al phases in Layer-II and BCC-Fe(Cr,Al) solid solution phase in Layer-III, with B2-NiAl precipitates distributed in Layer-II and Layer-III. (2) After LSP treatment, a dislocation density gradient from the surface to the matrix, dislocation-precipitate interactions and a significant compressive stress were introduced. (3) Though the aluminized steel exhibited a decrease in the high temperature tensile properties compared to that of the as received 321 steel, the aluminizing + LSP processed steel achieved a striking enhancement. The formation of three-layer coating, dislocation density gradient, dislocation-precipitate interactions and the residual stress contribute jointly to gain the yield strength, ultimate strength and fracture elongation up to 265 MPa, 430 MPa and 37.5 % at 620 °C, respectively.

Microstructure Evolution and Growth of Interfacial Intermetallic Compounds in NiCr/Ti Alloy Laminated Composite after Explosive Welding and Heat Treatment

The paper considers the issues of interaction of the molten metal at the interface of explosively welded NiCr/titanium alloy laminated composites with the reaction zone formed during heat treatment, as well as the features of its destruction after welding. It was established that the molten metal is a heterogeneous mixture based on Ni(Cr,Ti) and Ti(Ni,Al) solid solutions and NiTi and Ni3Ti intermetallic compounds. The estimated existence time of molten metal areas in the liquid state was ~10−8–10−11 s. The obtained values are comparable with the time of the unloading wave arrival at the contact surface, which is the reason for the presence of fracture areas in the form of detachments on the fracture surface. Continuous nanometer-size interlayers with an amorphous structure, due to the ultra-high cooling rate of the liquid melt, induce viscous destruction of the interface. Heat treatment at temperatures of 700 and 850 °C led to the formation of a layered reaction zone at the NiCr/Ti boundary, consisting of interlayers of solid solutions based on Ti2Ni, TiNi, and TiNi3 intermetallic compounds, as well as inclusions of a Cr(Ti) solid solution. The diffusion flow gradient was predominantly directed into the titanium alloy.

Stabilizing Supersaturation with Extreme Grain Refinement in Spinodal Aluminum Alloys.

Supersaturated solid solutions can be formed in alloys from various non-equilibrium processes, but stabilizing the metastable phases against decomposition is challenging,particularly the spinodal decomposition that occurs via chemical fluctuations without energy barriers to nucleation. In this work, it is found that spinodal decomposition in supersaturated Al(Zn) solid solutions can be inhibited with straining-induced extreme grain refinement. For the refined supersaturated grains at the nanoscale, their spinodal decomposition is obviously resisted by the relaxed grain boundaries and reduced lattice defects. As grains are refined below 10nm the decomposition is completely inhibited, in which atomic diffusion is blocked by the stable Schwarz crystal structure with vacancy-free grains. Extreme grain refinement offers a general approach to stabilize supersaturated phases with broadened compositional windows for property modulation of alloys.

Improvement of Microstructure and Sliding Wear Property of Cold-Sprayed FeAl Intermetallic Compound Coating by Annealing Treatment

Nanograin Fe(Al) solid solution alloy coating was firstly produced through cold-spraying technology using mechanically alloyed powder. Then, the above-mentioned coating was annealed at different temperatures to explore its influence on the phase constitution, microstructure, microhardness and dry sliding wear property of the coatings. Results exhibited that an FeAl phase appeared in the coatings after 500 °C treatment and remained stable with increasing annealing temperature. The annealing temperature had a considerable effect on the microstructure, microhardness and wear behavior of the FeAl coating. The existing laminated structure in the as-sprayed coating gradually faded away with increasing temperature and finally obtained a dense coating microstructure with no particle interface when annealed above 950 °C. Nanograin began to evidently grow at temperatures over 800 °C. The microhardness of the FeAl coating stayed at 400 Hv0.1 at temperatures below 800 °C, then it quickly dropped to 300 Hv0.1 at 950 °C and remained nearly unchangeable up to 1100 °C. The dry sliding wear mechanism of the FeAl coating annealed at low temperatures below 700 °C was mainly delamination of the oxide layer and showed a high wear rate within the order of magnitude range of 10−4, whereas FeAl coatings annealed at high temperatures above 950 °C were worn by microploughing and little oxidation and exhibited very low wear rates within the order of magnitude range of 10−6.

Cu-10 wt.% Al Alloys Produced by Spark Plasma Sintering of Powder Blends and a Mechanically Alloyed Mixture: A Comparative Investigation

Cu–Al bronzes are interesting metallic materials, demonstrating higher hardness, higher wear resistance, higher corrosion resistance and a lower friction coefficient as compared with unalloyed copper. The powder metallurgy approach to the fabrication of these alloys presents opportunities to tailor their phase composition and grain size. In the present work, the structural characteristics, phase composition and properties of Cu-10 wt.% Al alloys obtained by spark plasma sintering (SPS) of powder blends and a powder obtained by mechanical alloying (based on Cu(Al) solid solution) are reported. Alloys with different interaction degrees between the metals were obtained by SPS. The blends demonstrated better sinterability than the mechanically alloyed powder: a nearly fully dense alloy was obtained by SPS of the blend at 480 °C, whereas a temperature of 800 °C was necessary to consolidate the mechanically alloyed powder. The hardness and electrical conductivity of the sintered alloys were comparatively analyzed. It was shown that the Cu-10 wt.% Al alloys obtained without the mechanical alloying stage possess hardness and electrical conductivity comparable to those of the alloys obtained from the mechanically milled powder.

An investigation on diffusion bonding of Mg/Al dissimilar metals using Zn-Bi alloy as interlayer

Diffusion bonding of AZ31 magnesium alloy and 5083 aluminum alloy with the interlayer of Zn-2Bi alloy was carried out at 335 ℃ under 4 MPa for 120–480 min. The results showed that the interface zone of the joints was consisted of Al(Zn) solid solution, Al-Zn eutectoid product (α + η), remnants Zn-2Bi alloy and MgZn2 intermetallic compounds (IMCs). The highest hardness of the joint was 255 HV which occurred in the MgZn2 IMCs region. The shear strength of the joint increased first and then decreased as the bonding time increased, and the maximum shear strength of 20 MPa was obtained when the bonding time was 360 min. For the joints with the bonding time of 360 min and 480 min, the shear fracture surface was at the interface of 5083/Zn-2Bi and at AZ31/Zn-2Bi, respectively, and the fracture mode of the both joints was brittle fracture.

EFFECT OF HIGH PRESSURE TORSION ON STRUCTURE AND MECHANICAL PROPERTIES OF Al–Ca–Cu ALLOY

To improve the balance of strength and ductility of the Al–6% Ca–8% Cu (wt %) alloy, the high-pressure torsion (HPT) deformation followed by annealing was applied. The structure of the as-cast alloy consisted mainly of two eutectics [(Al) + AlCaCu] and [(Al) + (Al, Cu)4Ca + AlCaCu]. HPT through three turns leads to the formation of a predominantly submicrocrystalline structure, refinement of eutectic particles and their more uniform distribution in the sample volume, calcium segregation from AlCuCa and (Al, Cu)4Ca particles, and supersaturation of the (Al) solid solution with copper. Such a structure provides a strengthening of the alloy by a factor of 3.5, but contributes to its embrittlement. Subsequent annealing at 400°C achieves a good balance of strength and ductility of the alloy.