Microalloying Elements Research Articles

Structure-property correlation for friction stir welded joints of 2219Al alloys microalloyed with Cd

Present study aimed at experimental investigation of microstructural evolution, microhardness profile, tensile and impact properties of friction stir welded (FSW) joints of 2219Al alloys microalloyed with varying (up to 0.1 wt%) Cd contents. FSW was performed on the cast and homogenized alloys. Microstructural analysis from weld line up to base metal, identified three sequential heat affected weld zones having separate grain morphologies, namely Weld Nugget Zone (WNZ), Thermo-Mechanical Affected Zone (TMAZ) and Heat Affected Zone (HAZ). Vickers microhardness value increased from weld line towards the WNZ, then decreased towards the TMAZ, and finally increased through HAZ towards the base metal, which exhibited higher hardness compared to all the heat affected weld zones. Microhardness, yield and tensile strengths of the FSW joint of 2219Al alloy increased, due to microalloying with 0.06 wt% of Cd contents, which was attributed to continuous grain refinement. While tensile ductility and toughness, and impact toughness of the welded joint reduced, resulting from trace additions of Cd. Investigated alloys retained significant mechanical strength, ductility and toughness, on the respective joints, following to the FSW operation. Cd was observed to be a potential microalloying element to control the microstructure, refine grain size and improve mechanical strength and hardness of the welded joint of 2219Al alloy. Present experimental results established a structure-property correlation, in order to validate potential application of FSW technique on investigated 2219Al alloys with trace additions of Cd, to attain desirable weld-quality avoiding welding imperfections.

Underlying mechanisms for the effect of Nb micro-alloying on the elemental distribution and precipitation behavior in the X70 weld metal

Niobium (Nb) is a widely recognized micro-alloying element due to its low cost and substantial impact on steel properties. While the effect of Nb in processed steels has been well investigated, studies on its elemental distribution and precipitation behavior in weld metal remain scarce. This study focuses on the weld metal of specially designed Nb-rich X70 pipeline steel by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) characterization, complemented with thermodynamic and kinetics modeling analysis. In the majority of the weld, Nb was essentially uniformly distributed. This suggests that Nb primarily exists in the solid solution form in the weld metal, which is also supported by precipitation kinetics modeling results. This is primarily due to the short thermal history associated with the welding process, which leads to insufficient time for the uniform precipitation of Nb. Two instances of Nb precipitates were observed at the weld centerline and reinforcement region. The low partition coefficient of Nb results in an elevated local concentration along the weld centerline. However, precipitation kinetics calculations suggest that this enhancement alone is not adequate to induce precipitate formation. The occurrence of MnS and the prior formation of Ti precipitates may provide heterogeneous nucleation sites for Nb, facilitating the nucleation of Nb precipitates in the weld centerline and reinforcement region.

Inverse design of high-strength medium-Mn steel using a machine learning-aided genetic algorithm approach

To develop medium-Mn steels with an ultimate tensile strength (UTS) exceeding 2 GPa and excellent ductility, we created a highly accurate UTS prediction machine learning (ML) model using a boosted decision tree model and 1520 dataset of tensile properties of medium-Mn steels with micro-alloying elements. We also optimized the hyper-parameters of a genetic algorithm (GA) using the Shannon diversity index to enhance search efficiency while retaining diversity. In a high-dimensional search space with millions of potential combinations, the ML-GA approach efficiently identified diverse chemical compositions and austenitizing conditions to achieve UTSs above 2 GPa. The k-means clustering method then grouped them into five distinct specimens based on similarities. These five specimens, fabricated using inversly designed chemical compositions and austenitizing temperatures, successfully exhibited UTSs exceeding 2 GPa and greater ductility compared to hot-stamped C steels. These excellent tensile properties were attributed to grain refinement resulting from the low austenitizing temperature and the pinning effect of micro-alloying element carbides, such as TiC and VC.

Improvement of strength in low-carbon Nb–Ti weathering steel through Ce microalloying

In this study, a high-strength low carbon Nb–Ti containing weathering steel was developed. The steel achieved a yield strength of 824.4 MPa and an elongation of 24.4% with the addition of 0.030% Ce as a microalloying element. Precipitation strengthening and dislocation strengthening contributed nearly 60% to the yield strength of the steel. The effects of Ce on the dissolution and precipitation behavior of microalloying elements were analyzed through experimental research and first-principles calculations. Additionally, the associated strengthening mechanisms were elucidated. The findings revealed that the Ce–Nb pairs within the 2 to 7 nearest-neighbor configuration in face-centered cubic Fe exhibited a mutual attraction. This attraction promoted the dissolution of microalloyed carbonitrides, leading to a reduction in the volume fraction of precipitates with diameters above 150 nm from 1.3% to 0.62%. Conversely, in the body-centered cubic Fe structure, Ce–Nb atom pairs were mutually repulsive across all configurations. During the coiling process, the addition of Ce increased the formation of nanoprecipitates in the 0.030% Ce–Nb–Ti weathering steel. Particularly, the volume fraction of precipitates with diameters ranging from 20 to 150 nm in the steel increased from 1.6% to 2.7%, while the fraction of nanoprecipitates also increased from 0.051% to 0.31%. The nanoprecipitates formed within the dislocation substructure of the ferrite significantly enhanced steel strength but reduced its plasticity. Additionally, the addition of Ce led to the formation of numerous fine cementite particles in the localized areas of the steel matrix, which contributed up to 49.2 MPa to the overall strength of the steel.

Discharge Properties and Electrochemical Behaviors of Mg-Zn-xSr Magnesium Anodes for Mg-Air Batteries.

In this work, the electrochemical and discharge properties of Mg-Zn-xSr (x = 0, 0.2, 0.5, 1, 2, and 4 wt.%) alloys used as anodes for Mg-air batteries were systematically studied via microstructure characterization, electrochemical techniques, and Mg-air battery test methods. The addition of Sr refines the grain size, changes the composition and morphology of the passivation film and discharge products, and enhances the electrochemical properties of the alloy. Excessive Sr addition breaks the grain boundaries and precipitates a large number of Sr-rich phases, resulting in microgalvanic corrosion and the 'chunk effect'. The anode efficiency of Mg-Zn-1Sr is the highest at a current density of 10 mA cm-2, reaching 61.86%, and the energy density is 2019 mW h g-1. Therefore, Sr is a microalloying element that can optimize the electrochemical performance of Mg-air battery alloy anodes.

Influence of microalloying on precipitation behavior and notch impact toughness of welded high-strength structural steels

Microalloying elements such as Nb and Ti are essential to increase the strength of quenched and tempered high-strength low alloy (HSLA) structural steels with nominal yield strength ≥ 690 MPa and their welded joints. Standards such as EN 10025–6 only specify limits or ranges for chemical composition, which leads to variations in specific compositions between steel manufacturers. These standards do not address the mechanical properties of the material, and even small variations in alloy content can significantly affect these properties. This makes it difficult to predict the weldability and integrity of welded joints, with potential problems such as softening or excessive hardening of the heat-affected zone (HAZ). To understand these metallurgical effects, previous studies have investigated different microalloying routes with varying Ti and Nb contents using test alloys. The high-strength quenched and tempered fine-grained structural steel S690QL is the basic grade regarding chemical composition and heat treatment. To evaluate weldability, three-layer welds were made using high-performance MAG welding. HAZ formation was investigated, and critical microstructural areas were identified, focusing on phase transformations during cooling and metallurgical precipitation behavior. Isothermal thermodynamic calculations for different precipitations were also carried out. Mechanical properties, especially Charpy notch impact toughness, were evaluated to understand the influence of different microalloys on the microstructure of the HAZ and mechanical properties.

Stabilization Effect of Interfacial Solute Segregation on θ′ Precipitates in Al-Cu Alloys

The effects of Sc, Mg and Si elements in an Al-Cu alloy have been studied by means of hardness tests and transmission electron microscopy analysis. The experimental results show that additions of Sc, Mg and Si can improve the heat resistance of the Al-Cu alloy. The Sc/Mg/Si segregation-sandwiched structure is the most stable, when compared with Sc segregation or Si/Sc co-segregation at the interface of θ′/Al. The additions of Si and Mg promote the aging–hardening response of the Al-Cu alloy. Mg is a micro-alloying element with great potential in stabilizing the size of θ′ phases, which further promotes the number density greatly. Consequently, the Al-Cu alloy achieves a high strength, matched with excellent thermal stability, due to the microalloying of Sc/Mg/Si solutes.

Niobium: The unseen element - A comprehensive examination of its evolution, global dynamics, and outlook

Niobium, a critical but often overlooked material, plays a crucial role in the Anthropocene era. Serving as a microalloying element in steel, typically at concentrations of 0.05–0.15 wt.%, niobium significantly enhances steel properties. Despite its pivotal role in structural, automotive, pipeline, and alloy sectors, niobium's importance is often unnoticed due to its low concentration in steel. This study employs dynamic and static material flow analyses (MFA) from 1950 to 2022, emphasizing environmental impacts and forecasting trends up to 2050 to unveil the evolution, global dynamic flows, and prospects of niobium. The MFA showed that in the 2000–2022 period, 996 Mt of niobium remains in use, 19 Mt was recycled, and a projected loss of 977 Mt is anticipated if no actions are taken. This emphasizes the critical need for sustainable practices in managing end-of-life niobium-bearing applications, with substantial potential for reutilization within a closed loop in the steel industry.

First-principles insights into solute partition among various nano-phases in Al−Cu−Li−Mg alloys

First-principles energetics calculations were performed over a group of 25 candidate elements, to investigate their partition energies and behaviors among major nano-phases (δʹ-Al3Li, θʹ-Al2Cu, T1-Al6Cu4Li3 and S-Al2CuMg) in most commercial Al−Cu−Li−Mg alloys. It was revealed that principal alloying element Li cannot directly affect θʹ and S, Cu cannot directly affect δʹ, Mg cannot directly affect θʹ and δʹ but can weakly partition into T1. As for micro-alloying elements, Si is the only element that can partition into all the four nano-phases. Au can partition into δʹ, θʹ and S. Cd can partition into δʹ, T1 and S. Zr can partition into δʹ and T1. Ni substitution can weakly partition into θʹ and S. Ti, V, Zn, Ag and Mo can partition into δʹ only. Cr, Mn, Fe and Co cannot directly affect any of the four nano-phases. Almost all RE-elements can strongly partition into T1, δʹ and S, but would be expelled by θʹ. Only Sc is somehow particular to S, showing no partition preference in S. The newly obtained fundamental results could constitute a simple prototype database in support for the accelerated design of Al−Li based alloys and other related Al alloys.

Effect of microalloying additions on microstructural evolution and thermal stability in cast Al-Ni alloys

Enhancement of thermal stability in Al-Ni alloys through microalloying with slow-diffusing elements, specifically Zr, has been previously reported which is attributed to Zr segregation at the Al/Al3Ni interface. In this study, we explore the influence of microalloying Al-Ni alloys with Zr, Ti, V, and Fe on microstructural evolution, hardness, and electrical and thermal conductivity across a range of heat-treatment temperatures from 300 to 450 °C. The distribution of microalloying elements and precipitates after heat treatment is characterized using atom probe tomography (APT). Our investigation confirms Zr segregation to the Al/Al3Ni interface, while similar interfacial segregation is absent with the addition of Ti, V, and Fe. Additionally, our analysis of the Al3Ni microfiber morphology reveals that their coarsening and spheroidization rates are similar with and without interfacial segregation; thus, retaining the fiber reinforcement through interfacial segregation of slow diffusing elements may not be an effective strategy. Precipitation of L12 nanoparticles was found to be the dominant mechanism affecting enhanced hardness and electrical conductivity in Al-Ni-Zr alloys, attributed to precipitation strengthening and solute depletion, respectively. Similar precipitation was not observed for additions of Ti, V, and Fe following heat treatment. We provide a thermodynamic explanation for this limitation. The findings of this study suggest that an effective approach for designing Al-Ni alloys should involve prioritizing microalloying elements to maximize L12 precipitation and minimize solute content in the FCC-Al matrix post heat treatment, rather than focusing on Al/Al3Ni interfacial segregation.

Research on the strengthening mechanism of Nb–Ti microalloyed ultra low carbon IF steel

Interstitial free (IF) steels are characterized by their interstitial free ferritic matrix due to addition of micro-alloying elements that draw carbon and nitrogen out of matrix to form carbonitrides. The IF steels typically have excellent deep drawing ability, certain mechanical strength, and high plastic deformation performance. In this paper, the microstructure evolution and carbides precipitation behavior during the hot rolling, cold rolling and annealing processes have been studied using both experimental and thermodynamic and kinetic modeling approaches. The strengthening mechanism of Nb–Ti microalloyed IF steel has been investigated. The results of the thermodynamic simulation indicates that the addition of Nb into Ti bearing IF steel promotes recrystallization at 900 °C, leading to fine recrystallized grains. Due to the recrystallization of austenite during the final rolling process, Nb–Ti microalloyed hot rolled plates exhibit finer grain size, fewer substructures, and lower dislocation density compared to the hot rolled plates containing only Ti. Building upon the initial fine and uniform structure, Nb–Ti microalloyed steel maintains a refined structure after undergoing cold rolling and annealing. The study of the carbides precipitation behavior suggests that TiN precipitates at high temperature above 1100 °C, while a substantial amount of (Nb,Ti)C and TiC precipitate at about 900 °C in Nb–Ti and Ti bearing steels, respectively. There is no significantly difference between the amount of carbides in steels hot deformed at 900 °C and in the hot rolled plates, indicating that the carbides mainly precipitate during the hot rolling process. There are negligible carbides precipitated during the coiling process at 600 °C. In Nb–Ti containing steel, Nb and Ti in solid solution are significantly reduced due to the large amount precipitation of (Nb,Ti)C during the final rolling process. The reduction of solid solution Nb effectively promotes the recrystallization of austenite. Therefore, the grains of hot-rolled, cold-rolled, and annealed strips are refined. In addition, there are more small size carbides in Nb–Ti bearing steel than that in Ti bearing steel. Therefore, the higher strength of Nb–Ti steel is mainly from the strengthening effect of grain refinement and carbides precipitation.

Prediction improvement of compressive strength and strain of directionally solidified TiAl alloy based on training data size adjustment

Compressive strength and compressive strain, which are important mechanical properties of directionally solidified TiAl alloy, were predicted using machine learning algorithms, specifically Multiple Linear Regression (MLR), and Random Forest Regression (RFR). The input variables for the machine learning model were designated as the composition of the directionally solidified TiAl alloy, experimental parameters (pulling velocity, input power), and compression test parameters (strain rate, compression temperature). Compressive strength and compressive strain were designated as the output variables. Although the typical ratio of training and test data is 8:2, this study used different ratios of 9:1, 7:3, and 6:4 for machine learning, and excellent R2 values were obtained for all ratios. The feature importance, which can identify the factor that has the most influence on the output variables, was obtained through the RFR algorithm. According to the feature importance, temperature was found to have the greatest influence on compressive strength, while the Erbium (Er) element had the most significant influence on compressive strain. Through the results of feature importance, it was possible to quantitatively investigate the relationship between the Er element, a microalloying element that affects the microstructure of TiAl alloy, and the compressive properties. Furthermore, the study was conducted on which data ratio between training and test data is most suitable for predicting the compressive strength and strain of TiAl alloy.

Optimizing the Heat Treatment Method to Improve the Aging Response of Al-Fe-Ni-Sc-Zr Alloys.

This work has studied the co-addition of Sc and Zr elements into the Al-1.75wt%Fe-1.25wt%Ni eutectic alloy. The changes in the microstructure, electrical conductivity, and Vickers hardness of the Al-1.75wt%Fe-1.25wt%Ni-0.2wt%Sc-0.2wt%Zr alloy during heat treatment were studied. The results showed that two-step aging can effectively improve the aging response of the alloy over the single-step aging method. This was ascribed to the minimization of the diffusion difference between Sc and Zr elements. Furthermore, the homogenization treatment can also improve the aging response of the alloy by alleviating the uneven distribution of Sc and Zr. Nevertheless, the micro-alloyed elements exceeded the solid solubility limit in the Al-1.75wt%Fe-1.25wt%Ni-0.2wt%Sc-0.2wt%Zr alloy, and their strengthening effect has ever achieved the best prospect. Finally, both Sc and Zr contents were reduced simultaneously, and the aging response of the Al-1.75wt%Fe-1.25wt%Ni-0.15wt%Sc-0.1wt%Zr alloy was improved by optimized heat treatment. The underlying mechanisms for this alloy design and the corresponding microstructure-mechanical property relationship were analytically discussed.

Influence mechanism of solution temperature on microstructure evolution and tensile properties of Ti microalloyed high strength steel CGLC700

The influence mechanism of solution temperature on the strength and toughness of Ti microalloyed steel CGLC700 was studied. The microstructure changes of Ti microalloyed steel were observed by micro-electron microscopy, and the mechanical properties were evaluated by tensile test. The appropriate solution temperature can promote the solid solution of Ti atoms and the formation of small-sized TiN, TiC and other particles, hinder the movement of dislocations, and improve the tensile properties of steel. When the solution temperature is 1240 °C (2#), the grain size of steel is the lowest, the proportion of high angle grain boundary is the highest, and the tensile properties of steel are the best. Ti microalloyed steels increased tensile strength by 4.12%, yield strength by 2.85% and elongation by 28.4%. Too low or too high solid solution temperatures weaken the strengthening effect of the microalloying elements and led to a reduction in the tensile properties of the steel. This can be attributed to the low solid solution of Ti at low solid solution temperatures and the growth of second phase particles and inclusions at too high solid solution temperatures. This study provides a theoretical basis for optimizing the heat treatment process of Ti microalloyed steel.

Effect of micro-alloying elements on the microstructure and properties of Ti-1300 alloy fabricated by directed energy deposition

In this research, Al0.5CoCrFeNi high-entropy alloy (HEA) multi-element micro-alloyed Ti-1300 alloy is fabricated by directed energy deposition. The microstructure, mechanical and electrochemical properties of Ti-1300 alloys are investigated. The average grain size of the Ti-1300 alloy is considerable reduced by 32.8% to 77.3 μm after micro-alloying. In addition, micro-alloying elements significantly improves the mechanical properties of the Ti-1300 alloy, with an increase in ultimate tensile strength of 13.4%, yield strength of 14.9% and average microhardness of 6.6%, while elongation remains essentially unchanged. Solution strengthening and refined crystalline strengthening are the dominant strengthening mechanisms. Electrochemical tests show that the micro-alloying elements results in a thicker and denser passivation film of Ti-1300 alloy in NaCl solution. This increases the resistance of the passivation film, leading to a reduction in both the corrosion current density and the corrosion rate. Multi-element micro-alloying is an effective strategy to improve the microstructure, mechanical and electrochemical properties of Ti-1300 alloy.

Micro-alloyed aluminium alloys as anodes for aluminium-air batteries with a neutral electrolyte

Aluminium (Al)-air batteries possess a low cost, high theoretical capacity, efficiency, and good recyclability. However, aluminium metal, as the anode material, suffers from low anodic efficiency and limited battery storage life. In this study, three extruded micro-alloyed Al alloys (Al-0.1Fe-0.3Si, Al-0.2Fe-0.2Si, and Al-0.2Fe-0.8Si) were investigated as anode materials for Al-air batteries in a neutral electrolyte. These three alloy anodes were also discharged in an alkaline electrolyte for comparison purposes. The results indicate that the micro-alloying elements Fe and Si accelerate corrosion in a neutral electrolyte. The composition of Fe and Si micro-alloying adversely affects the anodic performance of Al-air batteries but benefits the electrochemical activity of the aluminium substrate. In alkaline electrolytes, aluminium alloy anodes suffer severe self-corrosion and exhibit low anodic efficiency. Additionally, Al-0.1Fe-0.3Si and Al-0.2Fe-0.2Si alloys exhibit better battery performance than Al-0.2Fe-0.8Si at the current densities <10 mA·cm−2 in a neutral electrolyte.

Effect of Alloying and Microalloying Elements on Carbides of High-Speed Steel: An Overview

In high-speed steel, carbides are essential phase constituents, which have a direct impact on engineering performance and qualities of high-speed steel. The formation, morphology, and distribution of carbides are dictated by alloying elements. In this paper, various types of carbides in high-speed steel are presented. The effects of different alloying elements such as C, W, Mo, Cr, and V on the formation of carbides in high-speed steel are discussed. Research progresses on carbide improvement by microalloying elements such as N, B, Mg, and rare earth (RE) elements are reviewed. It is reported that Cr promotes the precipitation of M2C, N enhances the formation of fibrous M2C, Mg effectively shatters the large-size carbide grid, Nb refines granular carbide MC, and rare earth elements encourage the formation of M6C, resulting in irregular M2C lamellae. The incorporation of microalloying elements improves the distribution and size of carbides and also refines the solidification structure of high-speed steel.

Role of micro-alloying element in dynamic deformation of Mg-Y alloys

The microscopic mechanism of the effect of alloying element on the shock behavior for alloy materials is still limited. In this work, based on our developed Finnis–Sinclair (F–S) interatomic potential of Mg-Y alloy, using nonequilibrium molecular dynamics (NEMD) simulations, we gave new insights into the role of alloying element Y in dynamic deformation of Mg-xat.%Y (x = 1, 3, 6, 8 and 10) alloys, and further revealed the deformation mechanisms of these solid solution alloys, which is dependent on the compositions of Y and the crystallographic orientations. The results confirm that the lattice instability caused by Y atoms results in the reduced yield stress. Under shock along the [0001] direction, the improved plasticity is mainly attributed to the increasing amorphous activity and decreasing amorphous annihilation rate with Y additions, but the other mechanisms, e.g., the dislocation nucleation and phase transition, are suppressed. Furthermore, for the [101¯0] direction, the energy barriers of stacking faults and disordering can be overcome at high Y content, so these two deformation modes are activated accompanying with the lattice reorientation to release the large internal stress, and the enhanced plastic activity is mainly related to the inhibited phase transition. This work can broaden the knowledge of the dynamic response of Mg-Y alloys at atomic-scale, which is significant for the shock experiments and material design.

Mitigating hydrogen embrittlement of advanced high-strength steel by controlling carbides (cementite and alloy carbides) and microstructural modification

This work aims to demonstrate that the resistance to hydrogen embrittlement of conventional advanced high-strength steel (AHSS) with a bainitic ferrite structure can be significantly enhanced through two metallurgical strategies. Firstly, a smaller fraction of cementite in a mixture of bainitic ferrite and lath-martensite structures is realized by an intercritical annealing process with rapid cooling. Secondly, a higher fraction of alloy carbides (MC) with a mean size of less than 30 nm is formed through the combined addition of Ti, Mo, and V as micro-alloying elements. The reduction of cementite precipitation in the matrix leads to an increased resistance to hydrogen evolution/adsorption on the surface under cathodic polarization. Moreover, a large number of V-bearing nanoprecipitates ((Ti,Mo,V)-carbides and V-carbides) provides intermediate trapping for hydrogen atoms, effectively delaying the diffusion kinetics of hydrogen towards potential crack-forming areas in the matrix. Consequently, the lower strain reduction during slow strain rate test and the higher resistance to cracking during the four-point bending test in acidic aqueous solutions are manifested in the newly designed AHSS.

Changes in the structure and mechanical proper-ties of the aluminum alloy of the Al–Mg–Sc system as a result of treatment with a complex nanomodifier

Problem. On the basis of domestic and foreign research and the analysis of physicochemical properties of elements, the choice of scandium as a microalloying element of high-strength aluminium alloys is substantiated. The main criteria for the ability of scandium and its advantages over transition metals are given. Goal. The purpose of the work is to study the influence of a complex nanomodifier on the change in the structure and mechanical properties of aluminium alloy 1545 of the Al–Mg–Sc system. Methodology. For the first time, the treatment of aluminium melt with a complex nanodisperse modifier of the composition Mg2Si+SiС was proposed. The strength properties of aluminium alloys are significantly influenced by the size of the particles of the strengthening phase. Industrial experiments using dispersed particles of Mg2Si+SiС in a wide range of sizes of 50-100 nm. &#x0D; Results. The technology of modifying aluminium melt with a complex modifier has been developed. Originality. A homogeneous structure of the modified alloy 1545 with a grain size 2.7 times smaller than the original state was achieved. Practical value. In the work, the grain size was determined and it was established that the grain size of alloy 1545 was 15.6 mm2 before modification, and 5.7 mm2 after modification. As can be seen from the given data, as a result of the modification, the grain structure of alloy 1545 was crushed by 2.7 times. It was established that the maximum values of σ0.2 and σv correspond to the optimal content of the powder composition: 0.10% with a further increase of the modifier, the strength properties decrease, while the increase in the strength properties of the modified alloy is 12...18% compared to the initial state.