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).
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•Triple Sc-Fe-Si microalloying was exploited in an Al–Cu alloy to co-stabilize θ′-Al2Cu and Al3Sc precipitates during 300oC-creeping.•The Sc-Fe-Si co-segregation pattern at θ′-Al2Cu/matrix interface was produced by tuning solute repositioning to greatly suppressing the coarsening.•The Fe–Si synergy maximizes Si microalloying effect by preserving Si-promoted Sc precipitation while avoiding Si-accelerated Al3Sc coarsening.
•La microalloying method is proposed for grain refinement and texture weakness for copper tube annealed at high temperature.•Growth of recrystallized grain was effectively inhibited by second phase ...particles pinning and twin junction boundary drag.•Copper tubes with superior surface quality are successively fabricated with La microalloying method.
The effect of La microalloying on microstructure evolution of oxygen-free copper tube annealed at elevated temperature was investigated. Different with the significant grain growth in La-free copper tube, growth behavior of La microalloyed tube is effectively inhibited. Meanwhile, Cu6La particles are detected with mainly segregating near annealing twin boundaries but less at grain boundaries. With such experimental observations, a new mechanism for constrained growth of recrystallized grain is proposed with pinning of Cu6La particle coupled with annealing twin dragging. Moreover, refined microstructure is maintained for La microalloyed tube after elevated temperature, which greatly improves the surface quality during secondary bending and flattening processes.
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.
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•Magnetic properties can be controlled by adjusting annealing temperature.•The precipitated phase of Nb can provide remarkable fine-grain effect.•The {1 1 1} texture weakened and the {1 0 0} and ...{1 1 0} texture enhanced by increasing annealing temperature.•The experimental results can be widely used to control the microstructure and properties of high silicon electrical steel.
Fe-6.5 wt% Si alloy (high silicon electrical steel) is an ideal core material for making motors and transformers with low noise and low power loss. Controlling microstructure and texture is key to improving the magnetic properties of high silicon electrical steel. In order to improve the warm rolling and cold rolling workability of high silicon electrical steel, in this paper, 0.03 wt% Nb is added to the alloy, and a strip sample with a thickness of 0.13 mm was prepared. The effect of annealing temperature on microstructure, texture and magnetic properties of the samples was studied. The results show that annealing at 800 ℃–1300 ℃ for 1 h, with the increase of annealing temperature, the {1 0 0} texture content of the sample decreased from 9.47% to 1.09%, {1 1 0} texture content gradually increased from 1.26% to 33.1%, {1 0 0}+{1 1 0} texture content increased significantly from 10.73% to 34.19%. Nb-rich precipitates are formed in high silicon electrical steel with a size of about 100 nm. When the annealing temperature is lower than 1200 ℃, the Nb-rich precipitates can inhibit the grain growth. When the annealing temperature is higher than 1200℃, the Nb-rich precipitates dissolves and the pinning force to the grain boundary is weakened. The 0.13 mm Nb-microalloyed high silicon electrical steel strip has good magnetic properties at 800–1300 °C for 1 h. At 1200 °C, the grain growth and iron loss decrease due to the dissolution of the Nb-rich precipitates, so that the sample has a high comprehensive magnetic property: B8 is 1.31 T, B50 is 1.61 T, and P10/50 is 0.411 W/kg, P10/400 is 5.416 W/kg.
Fe83(Cox,Niy)(B11Si2P3C1)1-x,y/17 (x, y=1–3) amorphous alloys with high saturation magnetic flux density (Bs) and excellent soft-magnetic properties were developed and then the microalloying and ...clustering effects were explored. The microalloying of Co and Ni improves the Bs from 1.65T to 1.67–1.72T and 1.66–1.68T, respectively. The Ni-doped alloys exhibit better soft-magnetic properties, containing a low coercivity (Hc) of about 5.0A/m and a high Effective permeability (μe) of (8–10)×103, whereas the microalloying of Co leads to a deteriorative Hc of 5.0–13.0A/m and a μe of (5–8)×103. Moreover, microalloying of Ni can increase the ductile-brittle transition (DBT) temperature of the ribbons, while a totally opposite effect is found in the Co-doped alloys. The formation of dense α-Fe(Co,Ni) clusters during annealing process is used to explain the distinct effects of Co and Ni microalloying on the magnetic properties and bending toughness.
As a kind of important light alloys, the Al alloys exhibit mechanical properties that are closely related to the microstructures. Changing the main alloying elements and adjusting heat treatments are ...usually approaches to tune the microstructure and hence artificially control the mechanical properties. However, the windows for the two approaches have become quite narrow, after extensive studies in the last half of century. Microalloying has become the most promising strategy to further modify the microstructure and improve the mechanical properties of Al alloys, among which the element of scandium (Sc) is especially powerful. In this paper, the recent progresses in Al alloys microalloyed with Sc are briefly reviewed, focusing on the microstructural characterization, strengthening response, and underlying mechanisms. The possible key research points are also proposed for the further development of Al alloys microalloyed with Sc and other rare earth elements.
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.
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•The Sc addition have a remarkable microalloying effect on the microstructures and mechanical properties of Al–Cu alloys.•The Sc-dependences of mechanical properties at room and at high temperatures are much different.•A nanostructural Sc-based hierarchy enhanced creep resistance is confirmed and the strengthening mechanisms are unraveled.
Al-XCu (X = 1.0, 1.5, and 2.5 wt%) alloys with and without 0.3 wt% Sc addition were prepared respectively. The effects of composition and heat treatment processes on the microstructural evolution ...were systematically investigated by using transmission electron microscope and atom probe tomography (APT). Both Al3Sc dispersoids and θ′-Al2Cu precipitates coexisted after artificial aging, and a strong Sc segregation at θ′-Al2Cu/matrix interfaces was detected and quantified through APT examinations. A Sc solute partitioning was demonstrated between in the Al3Sc dispersoids and at the θ′-Al2Cu/matrix interfaces, mediated by the Cu content. Increasing the Cu content, both the size and volume fraction of the Al3Sc decreased after solid solution treatment. As a result, the interfacial Sc segregation was accordingly intensified during subsequent aging treatment. A parameter of reduction in interfacial energy (Δγ), derived from APT analyses, was proposed to characterize the degree of interfacial Sc segregation. The coupling effect of Al3Sc dispersoids and θ′-Al2Cu precipitates on ductile fracture was discussed, where a micromechanical model was developed to describe a quantitative relationship between the fracture strain with Δγ as well as parameters of the Al3Sc dispersoids.
•Trace amount of Sc (< 0.5 wt%) improves the mechanical properties of the Al-20Zn-3Cu-xSc alloys.•Comprehensive microstructural investigation shows that Sc element induces macro- and micro-scopic ...structural changes.•Al grain size and large grains formed at grain boundaries are greatly reduced.•Formation of nanoprecipitates is facilitated by the addition of Sc, resulting in generation of local strain field.•Quantitative symmetry investigation shows that the formation of nanoprecipitates severely breaks the local symmetry of Al.
We demonstrate the effect of Sc microalloying on the mechanical properties of Al-20Zn-3Cu-xSc (x = 0, 0.1, 0.3, 0.5 wt%) alloys. Trace amounts of Sc addition (<0.5 wt%) simultaneously improve the mechanical strength and the ductility of the Al-20Zn-3Cu-xSc alloys. Among the developed alloys, the Al-20Zn-3Cu-0.3Sc alloy shows the highest tensile strength of 363 MPa with an elongation of 6.8%. Comprehensive microstructural investigation reveals that the Sc microalloying element induces macroscopic (~μm scale) and microscopic (~nm scale) structural changes. Macroscopically, the Al grain size and large particles typically formed in the grain boundaries are significantly reduced. Microscopically, the formation of nanoprecipitates is facilitated by the addition of trace amounts of Sc, resulted in generation of local strain field. Quantitative symmetry investigation then demonstrates that the formation of nanoprecipitates severely break the local symmetry of Al, which affects the mechanical properties of Al-20Zn-3Cu-xSc alloys.
•A crack-free René 104 superalloy with a refined microstructure was fabricated by SLM with the microalloying of Sc.•Al3Sc nanoparticles promoted the heterogeneous nucleation of Ni to refine the ...grains.•The cracking elimination was ascribed to the alleviation of enriched Mo, Zr and B and accumulated thermal stress.•The heightened tensile performance was due to the cracking elimination, refinement of grains and Al3Sc nanoparticles.
Cracking is the critical issue of “hard-to-weld” nickel-based superalloys, especially in the component fabricated by selective laser melting (SLM). In the work, the cracks of as-printed René 104 superalloy were successfully eliminated by microalloying with Sc. The formation of Al3Sc nanoparticles promoted the heterogeneous nucleation of nickel, resulting in a 74.7% reduction of grain size and a significant decrease in< 001 > texture intensity. Compared with the original René 104 alloy, the modified René 104 alloy exhibits the yield strength of 918 MPa, ultimate tensile strength of 1289 MPa and elongation of 13.9%, which are promoted by 16.8%, 40.6% and 256.4%, respectively. Significant grain refinement provides more grain boundary area, which is beneficial to alleviate the enrichment of low melting point phase forming elements (Mo, Zr and B) and the accumulation of thermal stress at grain boundary, thereby eliminating cracks. The improvement of mechanical properties is basically ascribed to the elimination of cracks, grain refinement and the formation of Al3Sc nanoparticles. These findings provide a new perspective for the research and application of “hard-to-weld” nickel-based superalloy prepared by SLM.
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