•The heat resistant Al-3.3Cu-2.5Mn-0.5Zr (wt.%) alloy is manufactured by electromagnetic casting (EMC).•In the as-cast structure, all Mn and Zr and most of Cu is dissolved in aluminum solid ...solution.•The fine structure of as-cast EMC rod implies its sufficient plasticity for cold rolling.•The Al20Cu2Mn3 and Al3Zr phase nano dispersoids form during annealing of the cold rolled strip at above 350 °C.•Annealing at 400 °C allows to reach the optimal combination of thermal stability and electrical conductivity.
The experimental heat resistant alloy Al-3.3Cu-2.5Mn-0.5Zr (wt. %) has been manufactured using the method of electromagnetic casting (EMC) providing solidification at an ultra-high rate (~104 °C/s). The microstructure, phase composition, mechanical and electrical properties of the alloy in as-cast state and after cold rolling followed by annealing has been extensively studied using both thermodynamic calculations and experimental analysis. The microstructure of the as-cast EMC rod consists of the fine Al2Cu phase inclusions and aluminum matrix where all Mn and Zr and most of Cu are dissolved. The annealing of cold rolled strip at 400 °C allows reaching the optimal combination of strength, electrical conductivity and thermal stability.
•The structure of the Al-Ni-La system with two invariant reactions is proposed.•The eutectic formed based on the Al3Ni and Al4La compounds has an ultrafine structure.•The fraction of eutectic exceeds ...16 vol% and its particles being 30–70 nm thick.•The ultrafine eutectic provides for a high strength and elongation of the alloy.
The phase equilibria in the Al-Ni-La system and the microstructure and mechanical properties of the alloys with varying La and Ni contents were investigated by using thermodynamic calculations (Thermo-Calc software), electron microscopy, energy dispersive spectrometer and tensile test. It is shown that the microstructure of the most promising alloys with La contents of up to 8 wt% and Ni contents of up to 5 wt% consists of Al primary crystals and ultrafine ternary eutectic (particle thickness is about 30–70 nm) which in turn consist of binary Al3Ni and Al4La compounds. However, at an excessive concentration of La and Ni, the formation of the previously undescribed Al9LaNi2 ternary compound is observed. The actual structure of the ternary diagram is proposed based on experimental data. Uniaxial tensile testing of the promising Al7La4Ni alloy in as-cast state revealed an ultimate tensile strength of about 250 ± 10 MPa, a yield strength of 200 ± 10 MPa and a ductility of 3.0 ± 0.2%.
•A novel Al-Ca-Ni-Mn alloy for laser-powder bed fusion technique is proposed.•A high hardness (~200 HV) of as-built sample is achieved.•The hardness decreases slightly after annealing at up to ...400C.•Predominant contribution of eutectic particles to hardening is explained.
Microstructure and hardness of the Al-Ca-Ni-Mn alloy fabricated by laser-powder bed fusion were studied in as-built condition and after annealing at 200–400 °C for 3 h. A formation of pseudoeutectic cellular structure and outstanding hardness of 200 HV were reported in the initial state. A decrease in hardness down to 161 HV after exposure at 300 °C and no further degradation occurred after heating up to 400 °C. The softening was accompanied by the growth of primary phase up to ~800 nm and eutectic phase to ~90 nm. The latter had the most contribution into hardening that was explained by Orowan looping mechanism.
The effect of high-temperature radial-shear rolling (RSR) on the strain and stress distributions in the cross-sections of processed rods has been studied using finite element method simulation for ...the industrial 7075 alloy and compared with that for the new Al7Zn2.8Mg0.7Ni0.55Fe0.2Zr alloy. The simulation has revealed a gradient strain distribution along the cross-section of the processed rods for both alloys. The lowest stress has been observed in the central part of the rods, whereas the peripheral zones have had the highest strain with a factor of more than 1.5. For both alloys, the maximum true strain localized in the peripheral zones of the rods (~10) has proven to be substantially higher than the true strain (~2.1) caused by change in the overall (linear) dimensions of the rods. The results of numerical simulation of the stress and strain distributions have been in a good agreement with the as-deformed structure. For example, we have observed the formation of a gradient structure consisting of deformed fibrous grains in the central parts of the rods (in the vicinity of their axes) whereas in the middle of rod diameter and in the surface layers that are exposed to the highest stress and strain the structure contained more equiaxed and finer grains formed during dynamic recrystallization. The results of uniaxial tensile tests have revealed that the mechanical properties of the 7075 alloy (UTS ~ 390 MPa, YS ~ 280 MPa and δ ~ 9.9%) after RSR are comparable to those of the new alloy the microstructure of which additionally contains fine intermetallic particles. Thus, radial-shear rolling can be considered as an efficient industrial technology of high-strength aluminum alloys allowing one to achieve a combination of high strength and ductility in as-processed materials with a gradient grain structure.
The Al-3.3Cu-2.5Mn-0.5Zr (wt%) alloy was manufactured by electromagnetic casting and further subjected to processing including cold rolling, drawing and annealing. Excellent processability of the ...alloy at cold rolling and drawing was observed due to the ultrafine as-cast structure. Annealing of the cold-rolled strip at 350 °C for 48 h insignificantly reduces the hardness, but the electrical resistivity (ER) decreases by almost 3 times (from 115 to 40 nΩm). The large deformation during rolling (reduction 98.4%) and high fraction of the Zr- and Mn-bearing nano dispersoids (Al20Cu2Mn3 and Al3Zr-L12) stipulated the high set of mechanical properties and electrical conductivity after annealing at 400 °C (UTS~330 MPa, YS~250 MPa, EL~7%, 42.5 IACS). A model of ER dependence on the phase composition was proposed. While at above 400 °C there is a good agreement between the calculated and experimental values, the scatter at lower temperatures is attributed to exposure times insufficient for achieving the equilibrium (Al) composition. Atom probe tomography was employed for observation of Cu, Mn and Zr concentrations in (Al) after annealing at 350–450 °C. According to the experimental results and root-mean-square calculations, annealing at between 350 and 400 °C allows achieving (Al) compositions close to the equilibrium in reasonable time while with decreasing temperature the diffusion of Zr in (Al) decreases and thus it requires extremely long exposures, e.g. at 300 °C it is about 23,000 h. From this viewpoint annealing at below 350 °C is unreasonable for achieving lower ER.
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•The Al-3.3Cu-2.5Mn-0.5Zr alloy was manufactured at an ultra-high solidification rate.•The alloy showed excellent processability in both cold rolling and drawing.•Annealing provides for the formation of a high fraction of the nano dispersoids.•Annealing at 400 °C provides the best set of mechanical and electrical properties.•A model of the electrical resistivity dependence on the phase composition is proposed.
Thermodynamic calculations and experimental studies including transmission electron microscopy (TEM), atom probe tomography (APT), microhardness and specific electrical conductivity measurements, and ...high temperature uniaxial compression tests have been carried out in order to determine the influence of indium trace addition on the structure and precipitation hardening response in Al–Si–Cu based casting alloy. Analysis of the hardness curves for aging at 175 °C has revealed that the peak hardness of the In-containing alloy is about 22% higher compared to the In-free alloy (140 vs 115 HV) and is achieved in a much shorter time of aging (2 h vs 10 h). TEM analysis of the peak aged samples has revealed that much finer precipitates of the θ′ phase with a higher number density are formed in the alloy with trace addition. Furthermore, fine spherical nanoparticles associated with θ′ phase platelets are found in the In-containing alloy structure. Quantitative APT analyses have revealed that the number densities of θ′-phase precipitates and the spherical nanoparticles are equal at the beginning of aging, while in the peak aged state the number density of the θ′-phase is at least two times that of the spherical nanoparticles. APT analyses have also revealed that in the near-peak aged state more than half of copper (∼2.0 wt.%) is still dissolved in the aluminum matrix of the In-free alloy in comparison with only 0.2 at. % (∼0.46 wt.%) copper for the In-containing alloy. The results of uniaxial compression tests of the peak aged samples have shown that the 250 °C yield strength of the alloy with trace solute is about 1.5 times that of the base alloy (259 vs 174 MPa). Thus, indium trace addition catalyzes the decomposition process making it more effective and complete which is beneficial for increasing the alloy strength at low and elevated temperatures.
The effect of 0.1 wt% (0.02 at%) Sn trace addition on the structure and phase composition of Al-Si-Cu based alloy has been studied using thermodynamic calculations (Thermo-Calc software) and ...experimental techniques (transmission electron microscopy (TEM), atom probe tomography (APT), hardness and specific electrical conductivity measurements). The Vickers hardness measurement made after aging at 175 °C revealed that the peak hardness of the Sn-containing alloy is about 22% higher than that of the Sn-free alloy (135 HV vs 115 HV). Moreover, the peak hardness is achieved in a much shorter aging time (4 h vs 16 h). Considerably finer precipitates of the θ′ phase (average length less than 60 nm and thickness 3–5 nm) with a substantially higher number density are observed in the Sn-containing alloy. Tiny, rounded particles most of which are associated with the θ′ phase precipitates are also observed. Atom probe tomography analysis confirmed that the observed nanoparticles consist of tin. Quantitative APT analysis revealed that the number density of the copper-containing precipitates is at least twice that of the tin-containing ones (7.6·104 vs 3·104 µm-3). APT data also revealed a clear evidence of noticeable dissolution of Sn (average concentration from 0.05 to 0.10 at%) and silicon (average concentration from 2.2 to 2.8 at%) at the core of the θ′ phase precipitates, which is consistent with the fact that Sn and to a lesser extent Si act as catalysts in the nucleation of this phase. The data obtained using the proxigram technique suggest that Sn atoms show no tendency to segregate at the coherent θ′/(Al) heterophase interface upon aging, whereas localized Sn segregation is observed at the semi-coherent interface. Both Sn-free and Sn-containing alloys in their peak aged states have been subjected to uniaxial compression tests at an elevated temperature of 250 °С. The results suggest that the yield strength of the Sn-containing alloy is about 1.5 times that of the Sn-free alloy (250 MPa vs 175 MPa). The revealed difference is very big and testifies to a high potential of the new alloys as materials for new-generation engine parts.
•0.1% Sn addition in Al8Si3.5Cu alloy increases hardness by 22 % and catalyzes aging.•Fine Sn-containing particles attached to some θ′ precipitations are observed.•Number density of θ′ precipitates is three times that of the Sn-containing particles.•A noticeable dissolution of Sn (~0.1 at%) at the core of θ′ precipitates is observed.•Long-term aging decreases in the Sn core concentration down to 0.05 at%.
The effect of high-temperature radial-shear rolling (RSR) on the structure formation and mechanical properties of a new high-strength aluminium alloy based on the Al-Zn-Mg-Ni-Fe system was ...investigated by using transmission electron microscopy, scanning electron microscopy, electron backscatter diffraction, microhardness measurements and tensile test. The processed rod with a diameter of 14 mm was obtained from RSR at 480 °C after four passes with the corresponding elongation ratios: 1.67, 2.78, 5.53 and 8.16 (total value). The microscopic study showed that RSR of the billet led to the formation of a gradient microstructure with a deformed coarse-grained interior and a recrystallized ultrafine-grained surface. The recrystallized structure led to the decrease in microhardness up to 105 HV, whereas the preservation of non-recrystallized structure in the central parts provided an increased microhardness up to 145 HV. The fine crystals of the Al9FeNi eutectic phase and secondary precipitates of the Al3Zr and η(MgZn2) phases provided stability of the formed grain structure due to their high pinning ability. The subsequent analysis revealed that such a combination of structural components provides attractive mechanical properties. In particular, the results of uniaxial tensile tests revealed that the mechanical properties after RSR processing are comparable to the industrial 7075 alloy after equal channel angular pressing for the new alloy with composition Al-7.0% Zn-2.5% Mg-0.6% Ni-0.4% Fe-0.2% Zr (UTS ~ 430 MPa, YS ~ 310 MPa and δ ~ 7%).
•The model wrought heat-resistant Al–2%Mn–2%Cu alloy strengthened by Al20Cu2Mn3 precipitates is proposed.•The technological route for obtaining wrought products is free from homogenization and ...quenching.•The strength of model alloy is a much higher after annealing at 400 °С compared to the AA2219 alloy (YS 210 vs 90 MPa).•The Al20Cu2Mn3 precipitates retain the non-recrystallized structure even after annealing at 400 °С of the cold rolled sheets.
Cold-rolled commercial AA2219 and model Al-2 wt%Mn-2 wt%Cu(2Mn2Cu) alloys have been compared in phase composition, microstructure, physical and mechanical properties after different heat treatment routes. The as-cast structure of the model alloy proves to be similar to the homogenized structure of the branded alloy, providing a far shorter technological route required for obtaining a 95% cold reduction ratio. The principal possibility of obtaining cold rolled sheet products with a sufficiently high set of mechanical properties and electrical conductivity without the necessity of homogenization annealing, solution treatment, and water quenching has been shown. Electron microscopy, X-ray diffraction and Thermo-Calc software simulation have been used for optimizing the alloy composition. It has been shown that the as-cast structure of the model alloy has the minimum quantity of Al2Cu eutectic inclusions, and almost all manganese content and about 1.2% Cu are dissolved in the aluminum solid solution. This structure provides for a high plasticity that allows for deformation of ingots without their preliminary homogenization. The formation of the Al20Cu2Mn3 nano-sized dispersoids (with volume fraction of about 7 vol%) has been found to provide for the retaining of the fiber-like (non-recrystallized) grain structure in the model 2Mn2Cu alloy after annealing at 400 °С (3 h), despite a very high cold rolling reduction ratio (95%). The model alloy exhibits a substantially higher strength performance after annealing at 400 °С in comparison with the AA2219 alloy. For example, the YS value of the model alloy is 210 vs 86 MPa. This indicates a higher tolerance of the model alloy toward softening. Summing up the results, the ternary 2Mn2Cu model alloy shows a potential to become the basis for designing new high-tech heat-resistant alloys as a sustainable alternative to 2xxx alloys.
•The Sn trace addition catalyzes the precipitation hardening for the cast and wrought Al-Cu alloy.•The peak hardness is about 20% higher than that for the Sn-free alloy and is achieved much ...faster.•The Sn trace addition limits the growth of the Cu-rich phase leading to its as-cast spherical shape.
Experimental studies including microhardness and electrical conductivity measurements, transmission electron microscopy (TEM) together with atom probe tomography (APT) have been carried out for exploring the influence of tin (Sn) trace addition on the structure and precipitation hardening response in Al-Cu based alloy after either casting or cold or hot rolling. It is shown that the Sn trace addition refines the Al2Cu phase in an as-cast Al3.5Cu0.1Sn (wt.%) alloy. The alloy showed an increase by about 20% the peak hardness (~120 HV) for both cast and wrought products as well as significant reduction in the aging time to peak hardness (from 12 h to 2 h at 175 °C). According to the TEM and APT, the increased hardness is due to the formation of much finer θ′-phase precipitates with high number density.
