Al2Cu Precipitate Research Articles

Atomic structures of interfacial solute gateways to θ′ precipitates in Al-Cu alloys

Many materials employed in critical structural applications depend upon metastable strengthening precipitates that transform or dissolve at elevated temperatures. Herein, aberration-corrected scanning transmission electron microscopy and first-principles calculations are used to accurately determine the atomic structure of the highly mobile, semi-coherent precipitate interfaces that control this process in the classic θ′ (Al2Cu) precipitate in the Al-Cu system. Semi-coherent {110} interfaces are found to be composed of an array of unexpected misfit dislocations that are arranged in two different structural units. Dislocations accommodate nearly all of the misfit between the Al matrix and strengthening phase. Cu is observed to segregate to the compressed edge of the dislocation cores at specific sites in this interface. First-principles calculations revealed the energetic landscape that facilitates these sites to become entry and exit gateways of Cu atoms in this semi-coherent interface. This investigation reveals critical features within semi-coherent interfaces that determine the thermal stability of precipitation-hardened alloys.

Microstructures and mechanical properties of 4 wt%TiB2/Al-Si-Cu-Zn (T6) composite thin-walled shell housing fabricated by high pressure die casting

The application demand of lightweight high-quality aluminum alloy parts in automotive and aerospace fields is increasingly. In aluminum matrix composites, reinforcing particles can significantly improve the performance of the matrix. In this paper, the microstructures and mechanical properties of die-cast 4 wt%TiB2/Al-9Si-3Cu-0.8Zn composite were systematically analyzed by x-ray diffraction, optical microscope, scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy and tensile testing. The composite was successfully fabricated from an Al-K2TiF6-KBF4 system by in situ melting technique. The research results show that the average grain sizes of the α-Al phase gradually decreased with the increase of filling distance. And the TiB2 particles were distributed around eutectic Si in irregular polyhedral morphology or nearly circular shape. Meanwhile, the crystal structures of Ti-B compound and long needle shaped nano-sized precipitated were identified and analyzed, and they were found to be TiB2 and Al2Cu phase, respectively. Tensile testing results show that the mechanical properties of die-cast composite clearly increase after T6 heat treatment. The yield strength, ultimate tensile strength and elongation could reach 311 MPa, 379 MPa and 2.8% respectively, with the best injection velocity (1.8 m s−1). The significantly enhancement of mechanical properties of composite after T6 heat treatment was mainly due to the introduction of TiB2 reinforcing phase and the precipitation of Al2Cu precipitate in the aging stage. The results implied that the introduction of TiB2 reinforced particles could improve the mechanical properties of die castings, which has an important guiding role for its practical application.

The effect of major constituents on microstructure and mechanical properties of cast Al-Li-Cu-Zr alloy

The effect of major constituents (the Li content increases from 0.5 to 3 wt% and the Cu content decreases from 4.5 to 2 wt%) on microstructure and mechanical properties of cast Al-Li-Cu-Zr alloy were studied to understand a qualitative assessment of sequence and kinetics of multiple precipitations. Increasing the Li content progressively raises the melting temperature from 520 °C in 1# alloy (Al-0.5Li-4.5Cu, wt%) and 2# alloy (Al-1Li-4.5Cu) to 560 °C in 6# alloy (Al-3Li-2Cu). In addition, the variations of the major constituents result in the changes of the type and volume fraction of the inter- and intra-granular intermetallic phases. TEM results indicate that minor modifications to alloy composition greatly alter precipitation behavior during isothermal aging. The Li-poor alloy (2# alloy) presents a much shorter incubation time of T1-Al2CuLi precipitate than the Li-rich alloy (Al-1.5Li-4.5Cu, 3# alloy), while the nucleation of θ'-Al2Cu precipitate is promoted in Li-rich alloy. No typical spherical δ'-Al3Li precipitate is observed in 2# and 3# alloys during isothermal aging, except for the as-quenched 3# alloy. The preferential nucleation of δ' precipitate on the coherent and broad face of θ' precipitate is observed in 2# and 3# alloys, leading to the formation of “sandwich-like” δ'/θ'/δ' phases. Further decreasing Cu content to 2 wt% and increasing Li content to 3 wt% (6# alloy), the predominant phase in the matrix is δ' precipitate, accompanied by a small amount of unevenly distributed θ' and T1 precipitates. The best balance between ductility and strength is obtained by 2# alloy aged for 32 h, but 6# alloy has significant advantages in terms of density (2.437 g/cm3) and elastic modulus (82.65 GPa) over 2# alloy (density: 2.675 g/cm3; elastic modulus: 75.45 GPa).

Solute repositioning to tune the multiple microalloying effects in an Al–Cu alloy with minor Sc, Fe and Si addition

Abstract For multicomponent Al-based alloys, one of the most valuable approaches of microstructural design is to find a path to maximize the multiple microalloying effects while overcoming their negative counterparts. In this paper, triple Sc-Fe-Si microalloying was performed in an Al–Cu alloy to assemble the co-existence of θ′-Al2Cu and Al3Sc precipitates. Besides, the mutual interactions among triple microalloying elements were utilized to maximize the positive effects on tailoring the dual precipitates, as illustrated in two goals of microstructural design: (i). As to θ′-Al2Cu plates, the multiple Sc-Fe-Si segregation at θ′-Al2Cu/matrix interface was preferentially created in the alloy before creep (as-aged condition). During subsequent high-temperature creep, such interfacial warden will be rapidly reinforced by solute repositioning, as a process of accumulating solutes diffusing from both inner θ′-Al2Cu precipitate and outer matrix to limit the interfacial migration. (ii). For Al3Sc precipitates, the beneficial Si microalloying effect on encouraging the nucleation of Sc-rich entities (precursor of Al3Sc) was successfully acquired during aging, while the detrimental Si effect on accelerating Al3Sc coarsening is generally prohibited by tuning Fe–Si synergy within Al3Sc interior. The establishments of (i) and (ii) enable the satisfactory dispersion as well as the outstanding thermal stability of dual precipitates in the current Al-Cu-Sc-Fe-Si system, leading to a good creep resistance at a high homologous temperature of 0.61Tm ~ 300 °C (where Tm is the melting temperature of the α-Al matrix).

Understanding the effect of hot extrusion on the evolution of microstructure and associated mechanical properties in sintered Al-Cu-Mg alloys

A systematic study was carried out to establish a structure-property correlation of Al-Cu-Mg powder metallurgy alloys as a function of extrusion temperature and strain rate. A series of hot extrusion tests were performed on a hydraulic press in the temperature range of 450 °C–550 °C and at a strain rate of 0.1–0.3 s−1. Superior mechanical properties were attained by the uniform distribution of precipitates and dispersoids during extrusion, as witnessed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe micro analyzer (EPMA) and X-ray diffractometry (XRD). The dynamic recrystallization (DRX) was facilitated with the increase in deformation temperature and a decrease in strain rate. Brass {110} 〈112〉, Copper {112}〈111〉 and S {123}<634 > texture components were developed due to extrusion and Cube {100}〈001〉 and Goss {110}<001 > orientations found to be strengthened (with maximum intensities ~7.04 times of any random orientation) due to deformation temperature. The final microstructure of extrudates indicated the presence of α-Al matrix, Al2Cu eutectic structure and Al7Cu2Fe compounds. Primary Al2Cu precipitate dissolved in the matrix with increasing temperature and decreasing strain rate of extrusion. Both dislocation density and residual stress reduced with an increase in extrusion temperature as estimated from nanoindentation experiments following established models. Both yield strength and young's modulus increased after extrusion due to grain refinement, work hardening, precipitate hardening, and dispersion strengthening. However, both decreased with increasing extrusion temperature and decreasing strain rate. The maximum hardness (1305.06 MPa), compressive yield strength (367.24 MPa) and residual stress (1267.609 MPa) were observed in the specimen extruded at 450 °C and 0.3 s−1.

Study of Natural and Artificial Aging on AlSi9Cu3 Alloy at Different Ratios of Returnable Material in the Batch.

Aluminum alloys currently play an important role in the production of castings in various industries, where important requirements include low component weight, reduction of the environmental impact and, above all, reduction of production costs of castings. One way to achieve these goals is to use recycled aluminum alloys. The effect of natural and artificial aging of AlSi9Cu3 alloy with different ratios of returnable material in the batch was evaluated by a combination of optical, scanning, transmission microscope and mechanical tests. An increase in the returnable material in the batch above 70% resulted in failure to achieve the minimum value required by the standard for tensile strength and ductility. The application of artificial aging had a positive effect on the microstructure and thus on the mechanical properties of experimental alloys. By analyzing the results from TEM, it can be stated that in the given cases there is a reduced efficiency of θ’-Al2Cu precipitate formation with an increase of the returnable material in the batch and in comparison with artificial aging, which is manifested by low mechanical properties.

Tailoring precipitation strategy to optimize microstructural evolution, aging hardening and creep resistance in an Al–Cu–Sc alloy by isochronal aging

Sc microalloying has been regarded as one of the most effective methods to improve the high-temperature resistance of Al-based alloys via additional Al3Sc precipitation. However, synergetic precipitation of Al3Sc and some conventional precipitates (i.e. θ′-Al2Cu) is usually difficult in traditional series Al alloys due to the huge temperature gaps between their formation, which limits the Sc microalloying effect in multicomponent systems. Here, an optimized isochronal aging strategy was illustrated in an Al–Cu-Sc alloy to achieve better ambient- and high-temperature properties in comparison to the artificially aged counterparts. A series of microstructural characterizations reveal that, upon isochronal aging, the Sc-rich entities preferentially form in regions adjacent to θ′-Al2Cu precipitates at relatively low temperature stage (~250 °C) and are responsible for refining the θ′-Al2Cu precipitation in Al–Cu-Sc alloy. At higher aging temperature (~300 °C), the preferentially formed Sc-rich entities will be collected by adjacent pre-existing θ′-Al2Cu precipitates, accompanying with additional Al3Sc formation in matrix. The coexistence of θ′-Al2Cu and Al3Sc precipitates realized by isochronal aging contributes to the improved aging hardening behavior as well as better creep resistance at 300 °C in Al–Cu-Sc alloy compared with its Sc-free or isothermally aged counterparts.

The growth mechanisms of θ′ precipitate phase in an Al-Cu alloy during aging treatment

The plate-shaped θ′ (Al2Cu) precipitate acts as one of the primary strengthening phases in Al-Cu alloys. The interface, especially the semicoherent interface, between Al-Cu solid solution (αAl) and θ′ phase contains a lot of clues about phase transformations. Thus, these interfacial structures in an Al-Cu alloy after high-temperature and longtime aging have been analyzed in detail using atomic-scale high-angle annular dark-field scanning transmission electron microscopy and first-principles calculations in this work. It was found that the lateral growth of θ' precipitates is subjected to a combination of several major mechanisms under this aging condition. Except for some common intermediate phases, two novel and striking structures were observed on the interface, which implies two alternative atomic diffusion mechanisms for θ′ precipitate growth. For one condition, the atomic diffusion from αAl to θ′ phase transformation adopts an interstitialcy mechanism based on additional Al atoms. For the other condition, the diffusion is carried out through Al atoms. Both mechanisms are distinctly different from the previous theory based on direct diffusion of Cu atoms. The first-principle calculations also confirm that these newfound diffusion processes are energetically favored.

Formula omitted] needle-shape precipitate formation in Al-Mg-Si alloy: Phase field simulation and experimental verification

β'' needle-shape precipitate structures significantly affect the mechanical properties of 6xxx aluminum alloys. In this study, a modified multi-phase field (MPF) method combined with the thermodynamic and kinetic databases provided with the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) method has been employed to investigate the morphological evolution of the monoclinic β'' precipitates in Al-Mg-Si alloy. Emphasis has been placed on understanding the influences of interfacial energy anisotropy and elastic interaction on the shape of β'' precipitates. It is shown that the high anisotropic strain alone cannot explain the needle shape of β'' precipitates. In the case of considering the contributions from both anisotropic interfacial energy and elastic interaction simultaneously, the simulations lead to the formation of unique micro-needle-like structures in age strengthening 6xxx Al alloy. The simulation results are compared with plate-shaped θ'(Al2Cu) precipitate in Al-Cu system, and verified with high-resolution transmission electron microscopy (HRTEM) images of needle-like β'' precipitates in Al-Mg-Si system.

Microstructural, microscratch and nanohardness mechanical characterization of secondary commercial HPDC AlSi9Cu3-type alloy

A key issue in producing high quality aluminum automotive components using High-Pressure Die Casting (HPDC) process is minimizing the amount of imperfections. In the present research work, by means of optical microscopy (OM), SEM, TEM and AFM characterization techniques, microstructural evolution of secondary commercial HPDC AlSi9Cu3-type alloy was studied. For this purpose, one Al-alloy called C1 containing nominal composition and a second one called C2 going out of specification were employed. In addition to metallographic characterization, Vickers and nanohardness and microscratch mechanical testing techniques were applied to analyze material behavior. Furthermore, complementary thermodynamic calculations were done to estimate alloy phases precipitation as function of temperature. Results indicate that globular and ramified dendrites are developed in C1 and C2 Al-alloys, respectively, due the major solidification time between them. In fact, gas porosity and shrinkage microporosity were detected. α-Fe particle increased in size but not in volume fraction, as Al2Cu and β-Fe intermetallics do. Mostly, it was found that α-Fe particle growth following a coring behavior, formed by nanospherical particles. Thus, main shrinkage microporosity is associated with Al2Cu precipitate, where shrinkage pores in alloy C2 present several nanoparticles located between dendrite arms, identify by SEM and TEM analysis. Finally, hardness of alloys differs in 30 HV values due intermetallics population, whereas nanohardness allowed measuring single value of each phase. Because no major nanohardness differences were observed, microscratch resistance behaves similar in both alloys. Hence, present microstructural/mechanical characterization results can be taken into account for redesign and improving commercial HPDC Al-components.

Effects of Nano yttrium and Spark Plasma Sintering on the Mechanical Properties of AA2024 Matrix Composites

The present research work investigates the effects of nano yttrium (Y) and SPS mechanism on various properties of AA2024-Y nanocomposites. Five nanocomposites are developed through SPS by reinforcing varying amounts of nano yttrium in the range of 0.1–0.5 wt% to the AA2024 powder matrix. An unreinforced AA2024 is also sintered by SPS as a benchmark to compare the mechanical properties. The microstructure characterization of the developed nanocomposites is carried out by optical microscope and field emission scanning electron microscope and the mechanical properties like microhardness and tensile strength is evaluated by computerized Vickers hardness testing machine and universal testing machine (UTM) respectively. The mechanical properties and the corresponding microstructures of composites are correlated. The experimental results showed that the mechanical properties gradually increased to a certain level and then decrease. There is a clear trend of initial increase and late decrease in the mechanical properties. An optimum amount of nano yttrium (0.3 wt%) addition is observed to be the maximum limit of reinforcement content to create favorable conditions during spark plasma sintering for the promotion of densification and Al2Cu precipitation in the α-Al matrix leading to an improvement in the mechanical properties of the nanocomposites. Among the developed composites, the highest hardness (130 HV), yield strength (YS) (386 MPa) and UTS (462 MPa) are obtained in the AA2024 composite sample reinforced with 0.3 wt% addition of nano yttrium. Densities close to theoretical density are achieved in all the composite samples.

Correlation between the microstructure and machinability in machining Al–(5–25) wt% Si alloys

The machinability of the Al–Si alloys becomes worse with the Si content increasing. This article explored the influence of Si content on the machinability including cutting forces and chip breakability in machining the Al–Si alloys. The change in machinability of the Al–Si alloys with different Si content attributes to the evolution of microstructure. The cutting forces when cutting hypoeutectic Al–Si alloys are higher than the hypereutectic alloys because only Mg2Si ( β-phase) precipitations are formed in the former one versus cooperative precipitation of Al2Cu ( θ-phase) and Mg2Si in the latter. With regard to hypereutectic Al–Si alloys, cutting force components decrease with the increase in Si content due to the formation of brittle primary Si, which induces the initiation of cracks in material removal process. Moreover, the cutting stability of Al–Si alloys is improved with Si contents in the range of 12–18 wt%, while deteriorates for the Si content of 25 wt%. Besides, the chip breakability is improved due to the increase in eutectic silicon in hypoeutectic and eutectic ranges and because of the formation of block-shaped primary Si for hypereutectic alloys. The optimization of Si content is 12–18 wt% with cutting speed not less than 150 m/min.

Effects of (Pr + Ce) Addition and Heat Treatments on Microstructure and Mechanical Properties of Al-5Si-1.2Cu Alloy

Effects of (Pr + Ce) addition and heat treatments on the microstructure and mechanical properties of Al-5Si-1.2Cu alloys were investigated using scanning electron microscopy, x-ray energy-dispersive spectroscopy, transmission electron microscopy, microhardness and tensile testing. The aspect ratio and average area of Si were determined by PRO PLUS 6 image analysis. By comparing the microstructures of the Al-5Si-1.2Cu alloys with (Pr + Ce) addition concentrations of 0.3 wt.%, 0.6 wt.% and 0.9 wt.%, it was found that the eutectic Si and Fe-rich phases were refined when (Pr + Ce) addition was 0.6 wt.%. After adding 0.6w.% (Pr + Ce), the long rods of eutectic Si and fishbones of the Fe-rich phase were changed into round particles and short rods. The short rod-like Al-Si-RE compounds were formed in the grain boundary. In addition, eutectic Si and Fe-rich phase were refined and spheroidized and more RE dissolved in modified alloy after solution treatment (520 °C, 6 h). After aging treatment (175 °C, 6 h), eutectic Si- and Fe-rich phases were finer and more spherical, and the nano-scale Al2Cu phases were precipitated. The microhardness (97HV), tensile strength (238.62 MPa) and elongation (5.23%) of the heat-treated Al-Si-RE alloys were 24.35, 24.18 and 50.72% higher than those of the unmodified alloy, respectively. The change in microstructure Si, Fe-rich phase, the formation of Al-Si-RE compounds at grain boundaries and precipitation of nano-scale Al2Cu led to significant improvement in the mechanical properties of the Al-5Si-1.2Cu alloy modified with Pr + Ce.

Effects of yttrium addition and aging on mechanical properties of AA2024 fabricated through multi-step stir casting

Abstract The effects of yttrium and artificial aging on AA2024 alloy were investigated. The developed samples were further subjected to artificial aging at 190 °C for 1−10 h with an interval of 1 h. The metallurgical characterization was done by scanning electron microscope and X-ray diffraction. The mechanical characterization like hardness and tensile strength of the samples was done using computerized Vickers hardness testing machine and universal testing machine. The microstructures revealed that addition of yttrium refined the α(Al) matrix and led to the formation of Al−Cu−Y intermetallic in the shape of Chinese script which strengthened the samples. Compared to the base metal, samples with yttrium addition showed better mechanical properties. The sample reinforced with 0.3 wt.% yttrium showed the highest mechanical properties with the hardness of 66 HV, UTS of 223 MPa, YS of 180 MPa, and elongation of 20.9%. The artificially aged samples showed that the peak hardening of all the samples took place within 5 h of aging at 190 °C with Al2Cu precipitation. Aging changed the intermetallic from Chinese script to the fibrous form. The optimum amount of yttrium addition to AA2024 was found to be 0.3 wt.%.

Improving Microstructural and Mechanical Properties of AA2024 Base Metal by Adding Reinforced Strip Width of AA7075 via Vertical Compensation Friction Stir Welding Technique

Improving microstructural and mechanical properties of AA2024 base metal reinforced with AA7075 via vertical compensation friction stir welding (VCFSW) have become a very vital research area to reinforce the weak part of nugget zone in welded joints. So this paper presents a novel and simple method to improve microstructural and mechanical properties especially ductility and fracture locations of welded aluminum joints by VCFSW technique. Anyhow, most of the welded parts are subjected to the forming processes so improvement in the property of ductility and fracture behavior of welded joints is required. One solution to increase ductility and improve fracture behavior of welded joints is the use of interlayer compensation strip width as a reinforcement which has superior mechanical properties between two blanks of base metal during friction stir welding process. The effect of changing interlayer compensation width was investigated on the microstructural characterization (by an optical microscope, scanning electron microscope and transmission electron microscope) and mechanical properties (using microhardness, tensile and bending tests). Microstructure observations revealed that the tailor-welded joint without compensation interlayer contains micro-voids in the stir zone, while in tailor-welded joints with compensation interlayer, the voids completely disappear on the microscale. X-ray diffraction detected that the use of compensation interlayer of AA7075 between two AA2024 blanks led to the appearance of two precipitates of intermetallic phases, Al2Cu and Mg2Zn, on grain boundaries of aluminum which improved ductility and fracture behavior of welded joints. Ductility enhanced till 54.4% at compensation interlayer width 2 mm when compared to the joint without compensation interlayer. Lower hardness values were detected at nugget zone in joint without compensation interlayer. By contrast, highest hardness values in the softened regions were obtained in compensation interlayer joints. Finally, the highest bending angle occurred without any cracks in case of compensation interlayer of 2 mm at ultimate bending load.

Improved strength and ductility of friction stir tailor-welded blanks of base metal AA2024 reinforced with interlayer strip of AA7075

Most of welded parts requires secondary forming process to meet the design requirements which makes the ductility of the joint an important parameter to be improved. To this end, we imped compensation layer of AA7075 aluminum alloy between two blanks of AA2024 aluminum alloy during friction stir welding. The effect of compensation layer width on the microstructure, microhardness, tensile strength and failure strain was investigated. XRD results showed that using AA7075 alloy compensation layer helped for precipitation of new intermetallic phases, Al2Cu and Mg2Zn, at the grain boundaries of Al grains. Tensile test results showed that the sample with 2 mm width compensation layer possess 18% improved strength and 54.4% improved failure strain compared with the joint without compensation layer. The failure strain of this joint was 16.8% which is almost that for AA2024 (17.2%). The improved strength was because of the grain refinement and the precipitation of Al2Cu and Mg2Zn intermetallics. While the improved failure strain was due to the higher content of Mg and Zn alloying elements in AA7075 alloy which precipitate on the grain boundaries facilitating the slipping between grains and provide more deformability of the global structure.

Underlying causes of poor mechanical properties of aluminum-lithium alloy electron beam welded joints

The measured tensile strength for the electron beam welded joint of 2195 aluminum-lithium alloy was only 60% of BM, corresponding to a drastic softening effect within the welded zone. Although hole defect worsened the tensile strength for the welded joint, the strengthening phase deficiency within welded zone, including T1 (Al2CuLi) and θ' (Al2Cu), was indeed the underlying cause for the poor mechanical properties of aluminum-lithium alloy electron beam welded joint. The primary reasons for strengthening phase deficiency were proposed. Measured by chemical testing method, the Li content within the welded zone was merely 0.71%, which was attributable to the excessive temperature up to 3573 K in melt pool, indicating that the Li evaporation loss was as high as 36%. The Li evaporation loss was the most crucial factor for the barren precipitation of strengthening phases. The high-density dislocation clusters within the welded zone suggested a too fast cooling rate during solidification process. The brittle quasi-crystal phase, T2 (Al6CuLi3), abundantly precipitated along grain boundaries, which badly overconsumed the atom of Li and Cu that were needed by T1 (Al2CuLi) and θ' (Al2Cu) precipitation, and, simultaneously, deteriorated the properties at grain boundaries.

Nanostructural Sc-based hierarchy to improve the creep resistance of Al–Cu alloys

Al-2.5 wt% Cu alloys with different Sc additions (0, 0.1, 0.3, 0.5 wt%) are studied in comparison to reveal the Sc microalloying effect on precipitation, room temperature mechanical properties, and creep resistance. The results show that the Sc addition into the Al–Cu alloys can effectively promote the precipitation of θ′-Al2Cu, reducing the size and narrow the size distribution. However, the Sc-dependences of mechanical properties at room and at high temperatures are much different. Although the 0.3 wt% Sc addition results in the densest homogeneous θ′-Al2Cu precipitation and hence the highest room temperature strength, the 0.5 wt% addition leads to the most improved creep resistance at 300 °C that is derived from a nanostructural Sc-based hierarchy, i.e., Al3Sc dispersoid/heterogeneous θ′-Al2Cu precipitate units, homogeneous θ′-Al2Cu precipitates, strongest Sc segregation at θ′/matrix interfaces, and Sc clusters. The nanostructural hierarchy with thermally resistant nanostructural features at different length scales provides a new way to develop advanced Al alloys with excellent high-temperature stability and mechanical properties. The strengthening mechanisms at room and high temperatures are respectively discussed.

The Impact of Aging Time on Structure and Corrosion Resistance of Aluminum 2091 Lithium Alloy for Aerospace Application

In need of aerospace and automotive industries, the aluminum lithium alloy becomes a worldwide topic because of its corrosion resistance, hardness, and categorized as a lightweight material. This alloy has high resistance to corrosion due to doped alloying element, such as copper. Addition of lithium to aluminum alloys lowers its density. This paper was meant to study the impact of aging time at 190°C for 24 hours, 42 hours, and 72 hours on aluminum alloy crystal. The materials had solutionized at 525°C for 5 hours and had quenched at water before it was artificially aged. Besides corrosion resistance, the structure of this alloy are change as the aging times rise that caused by Al2Cu precipitation. To examine the electrochemical response of this material, potentiodynamic curves were obtained for aluminium lithium alloy 2091 during standard test in natural deaerated 3.5% wt and 7.0% wt NaCl solution after heat treatment. The structure after heat treatment were characterized by using X-ray diffraction. The results showed that aging time modified the structure and lead to change the electrochemical behaviour.

Enhancement ductility of friction stir welded aluminum blanks AA2024 via adding interlayer strip width of AA7075

This paper presents a novel and simple method to improve and enhance the ductility of welded aluminum blanks by friction stir welding technique. Anyhow; most of welded parts are subjected to the forming processes; so the ductility of friction stir tailor-welded aluminum blanks is an important key property. One solution to increase ductility is the use of interlayer compensation strip width as a reinforcement which has superior mechanical properties between two blanks of base metal during friction stir welding process. The effect of changing interlayer compensation width was investigated on the microstructural characterization (by an optical microscope, scanning electron microscope and transmission electron microscope) and mechanical properties (using microhardness, tensile and bending tests). Microstructure observations revealed that the tailor-welded joint without compensation interlayer contains micro-voids in the stir zone; while in tailor-welded joints with compensation interlayer the voids completely disappear on the microscale. x-ray diffraction detected that the use of compensation interlayer of AA7075 between two AA2024 blanks led to the appearance of two precipitates of intermetallic phases, Al2Cu and Mg2Zn, on the grain boundaries of aluminum which improved ductility of welded joints. Ductility enhanced till 54.4 % at compensation interlayer width 2 mm when compared to the joint without compensation interlayer. Lower hardness values were detected at the nugget zone in joint without compensation interlayer. On the other side; highest hardness values in the softened regions were obtained in compensation interlayer joints. Finally; the highest bending angle occurred without any cracks in case of compensation interlayer of 2 mm at ultimate bending load.