Next Article in Journal
Industrial Sludge Valorization in Soil Application
Previous Article in Journal
A Study of the Creep-Fatigue Damage Mechanism of a P92 Welded Joint Using Nanoindentation Characterization
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Metals
Volume 15
Issue 1
10.3390/met15010054
metals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Microstructure and Tensile Property Tailoring of Al–5Mg (wt%) Alloy Combined with Continuous Rheo-Extrusion and Sc Modification

by
Bowei Yang
1,2,
Wenyue Liu
1,2,
Xin Liu
1,2,
Dalong Yang
3,* and
Minqiang Gao
3,*
1
State Key Laboratory of Metal Material for Marine Equipment and Application, Anshan 114021, China
2
Ansteel Beiing Research Institute Co., Ltd., Beijing 102209, China
3
Engineering Research Center of Continuous Extrusion, Ministry of Education, Dalian Jiaotong University, Dalian 116028, China
*
Authors to whom correspondence should be addressed.
Metals 2025, 15(1), 54; https://doi.org/10.3390/met15010054
Submission received: 5 December 2024 / Revised: 31 December 2024 / Accepted: 6 January 2025 / Published: 10 January 2025
(This article belongs to the Section Metal Casting, Forming and Heat Treatment)
Browse Figures
Versions Notes

Abstract

In this work, Al–Mg alloys fabricated by combining continuous rheo-extrusion (CRE) and Sc modification were proposed for producing Al–Mg alloys with high efficiency and superior mechanical performance. The microstructural evolution and mechanical property response of the CREed Al–5Mg alloy with Sc modification were investigated. The grain refinement and strengthening mechanisms induced by nanoscale Al3Sc-phase particles in the alloy were discussed. The results showed that an obvious grain refinement effect was achieved in the CREed Al–5Mg alloy as the Sc content increased from 0 to 0.5 wt%, and the average grain size decreased from 52.6 μm to 2.4 μm, respectively. The primary Al3Sc-phase particles formed during solidification behaved as heterogeneous nucleation sites for the α-Al matrix, while the nanoscale Al3Sc-phase particles achieved during CRE enhanced the driving force of continuous dynamic recrystallization and the Zener drag force. As a result, a superior grain refinement effect was observed. The ultimate tensile strength, yield strength, and hardness of the alloy were enhanced as the Sc content increased from 0 to 0.5 wt%. Grain boundary strengthening, second-phase strengthening, and dislocation strengthening were the main strengthening mechanisms of the CREed Al–Mg–Sc alloys.

1. Introduction

As a typical medium-strength aluminum (Al) alloy, Al–Mg alloys have a wide array of applications in the aerospace, transportation, and marine industries owing to their superior specific strength and good comprehensive performance [1,2,3]. The strength of Al–Mg alloys is improved due to the solid solution strengthening effect induced by the substantial solid solubility of Mg in the α-Al matrix [4]. Thus, Al–Mg alloys with high Mg content are expected to broaden the applications in the above fields [5,6]. However, high-Mg-containing Al–Mg alloys prepared through the conventional casting method tend to form divorced eutectic structures that are coarse dendrites and Al3Mg2-phase particles during solidification, leading to the deformation difficulty and high brittleness of the alloys [7]. Meanwhile, the formation of A13Mg2-phase particles decreases the solid solution content of Mg in the α-Al matrix. Therefore, a weakened solid solution strengthening effect of Mg and insufficient mechanical properties are achieved in Al–Mg alloys. The exhibited mechanical properties are closely related to the microstructures [8]. Thus, it is essential to tailor the microstructure and obtain improved mechanical properties of Al–Mg alloys.
Adjusting the main alloying elements, utilizing heat treatments, and adopting deformation techniques are the main methods to improve the microstructure and thereby artificially regulate the mechanical performance of metal materials [9,10]. Based on extensive studies and given their non-heat-treatable characteristics, the windows for the former two methods are quite narrow for tailoring Al–Mg alloys. Microalloying and deformation have become promising strategies to further modify the microstructure and improve the mechanical properties [11,12]. It is well-known that rare earth (RE) elements and nanomaterials have superior advantages of melt purification and grain/dendrite refinement even in a small amount, thus improving the microstructure and mechanical properties of non-ferrous alloys [13,14]. It is worth mentioning that scandium (Sc) has been referred to as the most effective microalloying RE element for Al–Mg alloys due to the introduced Al3Sc-phase particles of L12-type dispersoids with a similar lattice size to the α-Al matrix [15]. Furthermore, the primary Al3Sc-phase particles preferentially formed during solidification act as heterogeneous nucleation sites due to the low lattice mismatch and good coherency with the α-Al matrix [16]. In addition, the continuous segregation and the growth of brittle A13Mg2-phase particles are inhibited by the Al3Sc-phase particles, contributing to the refined and discontinuous Al3Mg2-phase particles [17]. Thus, significant grain refinement and enhanced mechanical properties are achieved in Al–Mg–Sc alloys. Zhou et al. [18] reported that the typical dendritic microstructures in the as-cast Al–5Mg (wt%) alloy were eliminated and changed into fine and equiaxed grain microstructures as the Sc content reached 0.4 wt%. As a result, the ultimate tensile strength (UTS) and yield strength (YS) were enhanced from 215.4 and 86.1 MPa to 280.2 and 153.6 MPa, respectively, followed by a decline in elongation (EL) from 22.2% to 14.8% [18]. Moreover, Al3Sc-phase particles are considered one of the most effective precipitation hardening particles compared with the other common particles in Al alloys [19]. However, Li et al. [20] pointed out that the grain refinement effect was limited upon further increasing the Sc content, which was attributed to the coarse and blocky Al3Sc-phase particles distributed near the grain boundaries playing no significant role in grain refinement and reducing the effective Sc content in the as-cast Al–3.8Cu–1.2Li–0.4Mg (wt%) alloy. Thus, the application amount of Sc in Al–Mg alloys is limited. Further increasing the Sc addition and forming a large amount of small-sized Al3Sc-phase particles with uniform distribution for grain refining and precipitation hardening seem to be effective approaches for developing Al–Mg–Sc alloys with high performance.
On the other hand, the shear stress induced by the inhomogeneous flow during deformation contributes to refinement of secondary-phase particles [21]. Meanwhile, the movement of dislocations and grain boundaries is hindered by the refined particles, accelerating the occurrence of recrystallization; hence, the grains are further refined, and the mechanical performance is improved [22]. However, the size of secondary-phase particles tends to be still micron-sized after one-pass deformation. Li et al. [23] investigated the microstructural evolution of an Al–6.0Mg–1.1Mn–0.19Er–0.1Zr (wt%) alloy during hot extrusion and found that the size of phase particles in the hot-extruded alloy was about 5 μm. Thus, severe plastic deformation (SPD) is expected to achieve refined secondary-phase particles and grains with high efficiency [24]. However, the common SPD methods, such as equal-channel angular pressing (ECAP) [25], high-pressure torsion (HPT) [26], and reciprocating extrusion (RE) [27], exhibit long manufacturing processes and limited production size. Thus, a low-cost, high-efficiency, and green deformation method combined with casting and SPD, referred to as continuous rheo-extrusion (CRE), is proposed to tailor the microstructure and mechanical properties of high-Mg-containing Al–Mg alloys that go from liquid to solid in one step [28]. During the CRE process, the high cooling rate during solidification is conducive to the refinement of primary grains/dendrites and secondary-phase particles, while the subsequent high shear strain contributes to the elimination and recrystallization of dendrites and grains, followed by the further refinement of secondary-phase particles to nanoscale [29]. However, few studies on Al–Mg alloys prepared through CRE and Sc modification have been reported. Therefore, the microstructural evolution of CREed Al–Mg alloys with different Sc content requires further investigation.
In this work, the Al–5Mg–xSc (x = 0.1, 0.3, and 0.5 wt%) alloys were manufactured through CRE. The microstructural evolution of CREed Al–5Mg alloys with different Sc additions was investigated. The strengthening mechanisms induced by nanoscale Al3Sc-phase particles on mechanical properties of the alloys were discussed. The aim of this work is to offer valuable insights into producing high-Sc-containing Al–Mg–Sc alloys through a high-efficiency processing technique and obtaining superior mechanical performance.

2. Materials and Methods

Al–5Mg–xSc (x = 0.1, 0.3, and 0.5 wt%) alloys considered in this study were prepared using high-purity Al (>99.994 wt%) ingots, Al–10.6Mg (wt%), and Al–2.08Sc (wt%) master alloys (provided by Beijing Ryubon New Material Technology, Ltd., Beijing, China). The alloy melt with different Sc content was produced in an intermediate-frequency furnace with high-purity argon protection. After all of the required elements were added during the smelting process, the melt (3 kg of each individual experiment) was heated up to 720 °C, followed by degassing and deslagging with C2Cl6, and then it was thoroughly stirred for composition uniformity and finally poured into the entrance of a wheel-shoe gap of a 300 series CRE device. The device is mainly composed of melting tundish, a melt flow channel, a rotational extrusion shoe, a fixed extrusion wheel, and a cooling system. The diameters of the extrusion wheel and the prepared alloy rods were 300 and 9.5 mm, respectively. Details of the device were described in recent studies [28,29]. The alloy rods were water-quenched after the CRE process. The actual chemical composition results of the alloy rods determined using a PerkinElmer Avio500 (Waltham, MA, USA) inductively coupled plasma-optical emission spectrometer (ICP-OES) are displayed in Table 1. The selected compositions were designed to increase, from the top to the bottom of the table, to promote the formation of Sc-containing phase particles in the alloys.
Specimens for microstructural characterization were cut along the extrusion direction (ED). The sectional dimension was 9.5 × 10 mm2. In detail, specimens for optical metallography observation were ground and polished using alumina sandpapers and diamond pastes, respectively, according to standard metallographic techniques. A Leica DMI 5000 M (Wetzlar, Germany) optical microscope (OM) was utilized to characterize the optical microstructure of the specimens under polarized light mode. The average grain sizes were measured via Image Pro Plus software version 6.0. The morphology, distribution, and composition of the secondary-phase particles were analyzed using a Zeiss Ultra Plus (Zeiss, Oberkochen, Germany) field emission-scanning electron microscope (SEM) equipped with a back-scattered electron (BSE) detector and an energy dispersive X-ray spectrometry (EDS) detector. X-ray diffraction measurements were obtained using the Bruker D8 (Billerica, MA, USA) Advance X-ray diffractometer (XRD) with Cu-Kα radiation for the phase analysis. The rated voltage and current of the XRD equipment were 60 kV and 80 mA, respectively. Furthermore, the scanning range and the speed utilized in this work were 20°~90° and 2 °/min, respectively. FEI G2 20 transmission electron microscopy (TEM) was performed to further observe the nanoscale secondary-phase particles in the alloys. The TEM specimens with a diameter of 3 mm were punched and ground to a final thickness of 60 μm and then electro-polished using the Tenupol-5 Struers twin-jet polisher (Struers, Ballerup, Denmark) in a solution of 30 vol% nitric acid and 70 vol% methanol at a temperature of −25 °C.
Specimens for mechanical performance testing were cut from the middle of the alloys. The specification of specimens was smooth and dog-bone-shaped with a circular cross section, and the gauge size was 6 mm in diameter and 30 mm in length. A Shimadzu AG-Xplus (Kyoto, Japan) electronic universal tensile machine was utilized for tensile testing at a strain rate of 10–3 s–1 under an ambient temperature of 25 °C. Three specimens for each condition were examined for reproducibility. A SIOMM HVD-1000MP Vickers hardness tester (Shanghai Jvjing Precision Instrument Manufacturing Co., Ltd., Shanghai, China) was used for Vickers hardness testing at an applied load of 200 gf and a dwell time of 10 s. The average value of nine indentations for each condition was considered as the final result.

3. Results

3.1. Microstructural Characterization

The typical optical microstructures and statistical average grain sizes of the CREed AM alloys modified by different Sc additions are displayed in Figure 1. On the contrary, no obvious dendrites but fine and equiaxed grains are observed in the CREed AM alloy, and the average grain size of the alloy is 52.6 ± 3.8 μm, as shown in Figure 1a. Compared with the AM alloy prepared through CRE, the grains are further refined in the AM alloy fabricated by combining CRE and Sc modification. As the Sc content increases to 0.1 wt%, the average grain size of the alloy decreases to 34.3 ± 2.4 μm, as presented in Figure 1b. An obvious grain refinement effect is achieved in the alloy upon further increasing the Sc addition to 0.3 and 0.5 wt%, and the average grain sizes are 11.2 ± 1.7 and 2.4 ± 0.6 μm, which are 78.7% and 95.4% declines in comparison to that of the CRE AM alloy, respectively, as displayed in Figure 1c,d. In addition, the statistical average grain size result of the CREed AM–xSc alloys is shown in Figure 1e.
Backscattered SEM micrographs of the CREed AM(–0.5Sc) alloys are displayed in Figure 2 for investigating the microstructural variation of the alloy after Sc modification. No obvious secondary-phase particles are precipitated in the CREed AM alloy, as presented in Figure 2a, which is consistent with the XRD analysis results in Figure 3. Furthermore, the EDS results of point A in the alloy are shown in Figure 2c, indicating that Mg atoms tend toward a solid solution in the α-Al matrix during the CRE process [30]. On the contrary, refined white secondary-phase particles with short rod-like or spherical morphologies are observed in the CREed AM–0.5Sc alloy, as shown in Figure 2b. The EDS results of point B are presented in Figure 2d, indicating that the white secondary-phase particles mainly consist of Al and Sc elements. Combined with the XRD analysis results in Figure 3, the Al–Sc-phase particles in the CREed AM–0.5Sc alloy are confirmed to be Al3Sc-phase particles [19].
Figure 4 presents the micrographs obtained through TEM of the AM(–0.5Sc) alloys manufactured through CRE. No obvious nanoscale secondary-phase particles are observed in the CREed AM alloy, as shown in Figure 4a, which is consistent with the conclusion above that Mg atoms are a solid solution in the α-Al matrix. Meanwhile, nanoscale Al3Sc-phase particles with typical petaloid-like morphology show a dispersed distribution in the CREed AM alloy with 0.5 wt% Sc modification, as presented in Figure 4b. The high-resolution transmission electron microscope (HRTEM) image indicates that the Al3Sc-phase particles have a completely coherent interface relationship with the α-Al matrix, which agrees with the previous studies [31,32].

3.2. Mechancial Properties

The variations in strength, ductility, and hardness have been measured to investigate the mechanical property response of the CREed AM alloys with different Sc additions. Figure 5 displays the engineering stress–strain curves of CREed AM alloys modified with different Sc content. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of the CREed AM alloy are 257.6 MPa, 99.8 MPa, and 52.8%, respectively. Meanwhile, the hardness of the CREed AM alloy is 69.8 HV. It is noticed that the UTS, YS, and hardness of the CREed AM alloy are enhanced upon increasing the Sc content, while the EL displays a tendency to decline. When the content of Sc reaches 0.1 wt%, the UTS, YS, and hardness of the CREed AM alloy are 331.3 MPa, 133.5 MPa, and 101.4 HV, respectively, followed by a decrease in EL to 41.8%. It is worth mentioning that an obvious improvement in mechanical properties is achieved in the CREed AM alloy with 0.5 wt% Sc modification. The UTS, YS, and hardness of the CREed AM–0.5Sc alloy are 456.4 MPa, 220.1 MPa, and 143.7 HV, which are 17.3%, 21.4%, and 13.6% enhancements compared to those of the CREed AM–0.3Sc alloy, respectively. Meanwhile, the EL of the CREed AM–0.5Sc alloy decreases to 24.8%, which is a 22.5% decrement in EL of the CREed AM–0.3Sc alloy. Table 2 lists the tensile properties and hardness results of the AM alloys prepared through CRE and Sc modification.

4. Discussion

4.1. Grain Refinement Induced by Sc Modification During Solidification

Compared with the CREed AM alloy, a superior grain refinement effect is achieved in the CREed AM alloy modified by Sc. It is well-known that undercooling and heterogeneous nucleation are the main methods for microalloying elements to refine the microstructures of Al alloys during solidification [33,34]. Owing to the chilling effect induced by the extrusion wheel and shoe during CRE, the cooling rate of the AM(–xSc) alloy melt is enhanced, thus contributing to the refinement of primary microstructures of the alloys. Moreover, the total undercooling (∆T) at the dendrite tips is described as follows [35]:
∆T = ∆Tt + ∆Tc + ∆Tr + ∆Tk
where ∆Tt and ∆Tc are thermal and solutal undercooling and ∆Tr and ∆Tk are curvature and kinetic undercooling, respectively. Due to the large atomic radius and low solubility of Sc in the α-Al matrix, Sc atoms tend to enrich in front of the solid–liquid interface during solidification [19]. Thus, solute redistribution occurs and solutal undercooling is enhanced upon increasing the amount of Sc, contributing to the reduction in the melting point, promoting the grain nucleation, and refining the grains of the AM–xSc alloys [18]. In addition, the growth restriction factor (QGRF) is utilized to describe the inhibition effect of Sc element enrichment on the grain growth of Al alloys, which is expressed as follows [36]:
QGRF = mSc CSc (kSc − 1)
where mSc is the concentration of solute Sc in the alloy melt and CSc and kSc are the liquidus slope and equilibrium partition coefficient in the Al–Sc binary alloy-phase diagram, respectively. Therefore, the growth restriction factor is enhanced upon increasing the Sc content. Furthermore, the Sc element’s enrichment at the solid/liquid interface tends to affect the diffusion of Al, inhibit the supplementation of Al in the liquid phase, and behave as a barrier to defer the growth of the primary α-Al matrix [37].
On the other hand, recent studies reported [11,19] that no compounds were formed with Mg and Sc, while Al3Sc-phase particles tended to form at a eutectic reaction temperature in Al alloys due to the low solid solubility of Sc in the α-Al matrix. In addition, the solubility of Sc in solid solution is decreased by the existence of Mg in Al alloys [16]. Thus, Al3Sc-phase particles tend to form in the alloy melt as the solidification temperature decreases. Based on the solidification theory [20], the heterogeneous nucleation potency of secondary-phase particles is closely related to the interfacial energy of the particle/matrix interface. The smaller the lattice misfit between particles and the α-Al matrix, the lower the interfacial energy, and stronger heterogeneous nucleation potency of particles is achieved [19]. The degree of lattice misfit (δ) is proposed to analyze the lattice misfit between the α-Al matrix and nucleated particles, as follows [38]:
δ = (α1 − α0)/α0
where α1 and α0 are lattice constants of secondary-phase particles and the α-Al matrix, respectively. Superior and moderate heterogeneous nucleation effects are obtained with a degree of lattice misfit below 6% and between 6% and 12%, respectively [39]. It is noticed that the lattice constant of Al3Sc-phase particles is close to that of the α-Al matrix with a similar crystal structure and consistency in orientation [19]. Thus, significant grain refinement is achieved due to the formation of primary Al3Sc-phase particles. However, primary Al3Sc-phase particles tend to form only when Sc addition reaches eutectic composition [18]. Thus, a limited grain refinement effect is achieved in the CREed AM alloy with Sc In addition, further grain refinement effect is obtained in the CREed AM–0.5Sc alloy, which is also related to the recrystallization process during CRE.

4.2. Grain Refinement Induced by Al3Sc-Phase Particles During Recrystallization

After solidification, the alloys undergo three stages of shear deformation during CRE, which are friction shear deformation, angular shear deformation, and extended shear deformation. The accumulative shear strain increases as the shear deformation proceeds. The total equivalent strain is calculated to be 3.8, and the primary Al6(Mn, Fe)-phase particles at the microscale are cracked and refined to the nanoscale during CRE [29]. Therefore, the high equivalent strain during CRE contributes to the uniform distribution and refinement of Al3Sc-phase particles in the AM–0.5Sc alloy, as presented in Figure 4. Moreover, continuous dynamic recrystallization (CDRX) is regarded as the main grain refinement mechanism during CRE [40]. The driving force of CDRX (Fd) is in direct proportion to the dislocation density (ρ) in Al alloys, which is presented as follows [41]:
Fd = 0.5Gb2ρ
ρ = ρAl + ρsp = ρAl + 6fvS/dspb
where G and b are the shear modulus and Burger’s vector of the α-Al matrix and ρAl and ρsp are the dislocation density of the α-Al matrix and the dislocation density increment induced by secondary-phase particles during deformation, respectively. fv and dsp are the volume fraction and the average diameter of secondary-phase particles, respectively. S is the shear strain during deformation. With the accumulative shear deformation during CRE, Al3Sc-phase particles in the AM–0.5Sc alloy are cracked and refined into nanoscale, contributing to the enhancement of fv and S. Meanwhile, dsp is decreased due to the formation of nano-sized Al3Sc-phase particles. Furthermore, the nano-sized Al3Sc-phase particles distributed within the grains have a strong inhibition effect on the dislocations in motion during deformation, which are beneficial for the enhancement of the driving force of CDRX and the refinement of grains in the alloy.
In addition, the Zener drag force (Fz), induced by the secondary-phase particles, is crucial to the migration velocity of grain boundaries and the grain size of Al alloys [42]. Thus, it is essential to analyze the Zener drag force generated by the nano-sized Al3Sc-phase particles, which is described as follows [41]:
Fz = 3fvγ/dsp
where γ is the grain boundary energy of the α-Al matrix. It is noticed that nano-sized Al3Sc-phase particles have strong impeding and pinning effects on the migration and growth of grain boundaries of Al alloys [19]. Meanwhile, the Zener drag force is enhanced, which is attributable to the fv increment and dsp decrement of Al3Sc-phase particles from microscale to nanoscale during CRE. Thus, a superior grain refinement effect is achieved in the CRE AM–0.5Sc alloy in comparison to the alloy without Sc modification.

4.3. Strengthening Mechanisms of the CREed AM Alloy with Sc Modification

Refined grains with enhanced mechanical properties are achieved in the CREed AM alloy with Sc modification. Thus, it is imperative to investigate the relationship between YS enhancement and microstructural variation and reveal the strengthening mechanisms of the CREed AM(–Sc) alloys. The yield strength of AM alloys is determined by the externally applied stress, which is crucial for driving dislocations to overcome various obstacles, such as Mg solutes, grain boundaries, nanoscale secondary-phase particles, and dislocation structures within the alloys [23]. Moreover, the Al matrix is strengthened by Mg solutes by directly pinning moving dislocations and indirectly dragging dislocations by diffusing to dislocation cores to form solute clusters [24]. Furthermore, the strength increment (∆σSS) induced by the above interaction approaches is expressed as follows [43]:
∆σSS = kSSCn
where kSS and n are material-related parameters and C is the Mg solute content in the Al crystal lattice. In this work, similar content and a fully solid solution of Mg atoms are achieved in the CREed AM(–Sc) alloys. Hence, the improvement of YS induced by Mg solute strengthening is insignificant. In addition, the strength enhancement generated by dislocation pileups at grain boundaries (∆σGB) is estimated using the Hall–Petch equation [17]:
∆σGB = kHPd−0.5
where kHP and d are the Hall–Petch coefficient and the average grain size of the CREed AM(–Sc) alloys, respectively. It is noticed that the obvious decrement in the average grain size from 52.6 μm to 2.4 μm is achieved in the CREed AM–0.5Sc alloy in comparison to the CREed AM alloy. Thus, a superior grain boundary strengthening effect is obtained in the CREed AM–0.5Sc alloy.
Furthermore, second-phase strengthening (∆σOr) induced by the interaction between nanoscale Al3Sc-phase particles and gliding dislocations via the Orowan mechanism is estimated using the following equation [16]:
∆σOr = Gb(fv/2π)0.5/3dsp
Hence, the second-phase strengthening effect is enhanced due to the formed Al3Sc-phase particles from micron-sized to nano-sized in the CREed AM–0.5Sc alloy in contrast with the CREed AM alloy with no secondary-phase particle precipitation.
Meanwhile, the dislocation structures formed during CRE have an inhibition effect on the slip of mobile dislocations and provide a superior dislocation strengthening (∆σDis) effect in the alloy, which is expressed via the Taylor equation, as shown below [29]:
∆σOr = αGbMρ0.5
where α, b, and M are the constant and the magnitudes of the Burgers vector and the Taylor factor, respectively. Massive studies have reported that nanoscale Al3Sc-phase particles and Mg solutes have a strong pinning effect on dislocations in motion. Hence, the dislocation density in the CREed AM–0.5Sc alloy is enhanced, and the dislocation strengthening effect is improved. The physical meaning and values of the symbols utilized in the calculation Equations (7)–(10) are summarized in Table 3. The calculated YS strength increment is 131.1 MPa, which is close to the experimentally measured YS increment (120.3 MPa). The difference between the measured and calculated results may result from the interaction between strengthening mechanisms [29]. Therefore, the strengthening mechanisms of the CREed AM–0.5Sc alloy are grain boundary strengthening, second-phase strengthening, and dislocation strengthening.
During tensile loading, plastic deformation of Al alloys is realized via dislocation slip [46]. However, the nanoscale Al3Sc-phase particles have a strong pinning effect on dislocations during motion, leading to the difficulty in dislocation slip [47]. Thus, inhomogeneous deformation still occurs between the Al3Sc-phases and the Al matrix. With the increase in strain, the stress concentration is further accumulated. As the accumulative stress concentration and inhomogeneous deformation exceed the critical value, microcracks form between the Al3Sc-phases and the Al matrix. The microcracks gradually grow, propagate, and connect with the neighboring microcracks. Consequently, circular cracks around Al3Sc-phase particles are formed. Therefore, the CREed Al–5Mg–xSc alloys with nano-sized Al3Sc-phase particles had low elongation in comparison to the CREed Al–5Mg alloys.

5. Conclusions

In this work, the microstructural evolution and mechanical property response of the AM alloy prepared through CRE and Sc modification were investigated. The grain refinement and strengthening mechanisms induced by nanoscale Al3Sc-phase particles in the alloys were discussed. The following conclusions were drawn:
(1) An obvious grain refinement effect was achieved in the CREed AM alloy, with the average grain size reduced from 52.6 μm to 11.2 μm as the Sc content increased from 0 to 0.3 wt%. A further reduction in the average grain size was obtained as the Sc content reached 0.5 wt%, representing a 95.4% decline in comparison to that of the alloy without Sc modification.
(2) The primary Al3Sc-phase particles formed during solidification acted as heterogeneous nucleation sites for α-Al matrix. Meanwhile, the nanoscale Al3Sc-phase particles achieved during CRE enhanced the driving force of the CDRX and the Zener drag force, resulting in a superior grain refinement effect.
(3) The UTS, YS, and hardness were enhanced with a loss in ductility as the amount of Sc increased from 0 to 0.5 wt%. Grain boundary strengthening, second-phase strengthening, and dislocation strengthening were the main strengthening mechanisms of the CREed AM alloy modified with Sc.

Author Contributions

Conceptualization, B.Y. and M.G.; methodology, B.Y.; software, W.L.; validation, W.L.; formal analysis, X.L.; investigation, B.Y. and X.L.; resources, D.Y.; data curation, W.L.; writing—original draft preparation, B.Y.; writing—review and editing, B.Y. and M.G.; visualization, D.Y.; supervision, D.Y. and M.G.; project administration, D.Y.; funding acquisition, M.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (Nos. 52371019 and 52301034), Natural Science Foundation of Liaoning Province, grant number (No. 2023-BS-170), and the Open Research Fund of Songshan Lake Materials Laboratory, grant number (No. 2023SLABFN11).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

Authors Bowei Yang, Wenyue Liu, Xin Liu are employed by the company Ansteel Beiing Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Zhang, H.T.; Zhang, Q.D.; Wang, F.Y.; Guo, C.; Yang, D.H.; Wang, Z.; Tang, X.C.; Li, Z.P.; Nagaumi, H. Influence of Mo on microstructure, mechanical properties and intergranular corrosion properties of Al–Mg–Mn alloys. J. Alloys Compd. 2024, 1007, 176284. [Google Scholar] [CrossRef]
  2. Nagaraja, S.; Anand, P.B.; Mariswamy, M.; Alkahtani, M.Q.; Islam, S.; Khan, M.A.; Khan, W.A.; Bhutto, J.K. Friction stir welding of dissimilar Al–Mg alloys for aerospace applications: Prospects and future potential. Rev. Adv. Mater. Sci. 2024, 63, 20240033. [Google Scholar] [CrossRef]
  3. Guo, W.; Zhuo, Y.C.; Zhao, Y.L.; Li, H.; Han, B.Y. Wetting behaviors of Al–Si–Cu–Mg–Zn brazing materials on 5083 aluminum alloy. Metals 2024, 14, 1183. [Google Scholar] [CrossRef]
  4. Tian, T.; Zha, M.; Jia, H.L.; Hua, Z.M.; Ma, P.K.; Wang, H.Y. The effect of high solid solution Mg contents (7–13 wt%) on the dynamic strain aging behavior of Al–Mg alloys. Mater. Sci. Eng. A 2023, 880, 145376. [Google Scholar] [CrossRef]
  5. Zha, M.; Zhang, H.M.; Meng, X.T.; Jia, H.L.; Jin, S.B.; Sha, G.; Wang, H.Y.; Li, Y.J.; Roven, H.J. Stabilizing a severely deformed Al–7Mg alloy with a multimodal grain structure via Mg solute segregation. J. Mater. Sci. Technol. 2021, 89, 141–149. [Google Scholar] [CrossRef]
  6. Raabe, D.; Tasan, C.C.; Olivetti, E.A. Strategies for improving the sustainability of structural metals. Nature 2019, 575, 64–74. [Google Scholar] [CrossRef]
  7. Liu, Z.B.; Sun, J.N.; Yan, Z.G.; Lin, Y.J.; Liu, M.P.; Roven, H.J.; Dahle, A.K. Enhanced ductility and strength in a cast Al–Mg alloy with high Mg content. Mater. Sci. Eng. A 2021, 806, 140806. [Google Scholar] [CrossRef]
  8. Jia, J.; Zhuang, W.; Li, J.; Cao, Q.; Liu, J. Effect of La on microstructure, mechanical properties and friction behavior of in situ synthesized TiB2/6061 composites. Metals 2024, 14, 1169. [Google Scholar] [CrossRef]
  9. Tian, N.; Liu, H.; Zhang, Z.S.; Liu, J.C.; Zhang, Y.Z.; Zhou, Y.R.; Zhao, G.; Qin, G.W. Portevin-Le Chatelier characterization of annealed Al–Mg alloy sheets with different Mg contents. Mater. Sci. Eng. A 2024, 893, 146118. [Google Scholar] [CrossRef]
  10. Zhou, D.S.; Zhang, X.Z.; Wang, H.; Li, Y.; Sun, B.H.; Zhang, D.L. Influence of Mg on tensile deformation behavior of high Mg-content Al–Mg alloys. Int. J. Plast. 2022, 157, 103405. [Google Scholar] [CrossRef]
  11. Jiang, J.Y.; Wang, H.L.; Tong, M.M.; Jiang, F.; Zhang, M.H. Effect of cryogenic environment on tensile property and microstructure evolution of an Al–Mg–Sc alloy. Mater. Charact. 2023, 195, 112550. [Google Scholar] [CrossRef]
  12. Mofarrehi, M.; Javidani, M.; Chen, X.G. Effect of Mn content on the hot deformation behavior and microstructure evolution of Al–Mg–Mn 5xxx alloys. Mater. Sci. Eng. A 2022, 845, 143217. [Google Scholar] [CrossRef]
  13. Borodianskiy, K.; Selivorstov, V.; Dotsenko, Y.; Zinigrad, M. Effect of additions of ceramic nanoparticles and gas-dynamic treatment on Al casting alloys. Metals 2015, 5, 2277–2288. [Google Scholar] [CrossRef]
  14. Borodianskiy, K. Effect of carbon nanotubes’ addition on mechanical properties and thermal conductivity of copper. J. Mater. Sci. 2019, 54, 13767–13774. [Google Scholar] [CrossRef]
  15. Ji, J.S.; Wang, L.L.; Lyu, F.; Gao, Z.N.; Zhan, X.H. Strength-ductility synergy of deposited Al–Mg–Sc alloy with a homogeneous phase distribution brought by heat treatment. Mater. Sci. Eng. A 2024, 913, 147034. [Google Scholar] [CrossRef]
  16. Zhang, H.M.; Zha, M.; Jia, H.L.; Tian, T.; Zhang, X.H.; Wang, C.; Ma, P.K.; Gao, D.; Wang, H.Y. Influences of the Al3Sc particle content on the evolution of bimodal grain structure and mechanical properties of Al–Mg–Sc alloys processed by hard-plate rolling. Mater. Sci. Eng. A 2021, 802, 140451. [Google Scholar] [CrossRef]
  17. Qiu, Y.C.; Yang, X.F.; Li, J.X.; Xiang, S.H.; Shi, J.; Xu, J.Y.; Sanders, R.E. The influence of Sc and Zr additions on microstructure and corrosion behavior of AA5182 alloy sheet. Corros. Sci. 2022, 199, 110181. [Google Scholar] [CrossRef]
  18. Zhou, S.A.; Zhang, Z.; Li, M.; Pan, D.J.; Su, H.L.; Du, X.D.; Li, P.; Wu, Y.C. Effect of Sc on microstructure and mechanical properties of as-cast Al–Mg alloys. Mater. Des. 2016, 90, 1077–1084. [Google Scholar] [CrossRef]
  19. Zhang, J.Y.; Gao, Y.H.; Yang, C.; Zhang, P.; Kuang, J.; Liu, G.; Sun, J. Microalloying Al alloys with Sc: A review. Rare Metals 2020, 39, 636–650. [Google Scholar] [CrossRef]
  20. Li, C.L.; Li, X.W.; Zhang, Y.A.; Wen, K.; Xiao, W.; Li, Y.N.; Yu, M.Y.; Gao, G.J.; Li, Z.H.; Xiong, B.Q. Effect of Sc content on microstructure characteristics and evolution of W phase in Al–Cu–Li alloys under as-cast and homogenization conditions. J. Mater. Res. Technol. 2023, 25, 7335–7352. [Google Scholar] [CrossRef]
  21. Yang, Z.; Tang, J.; Mo, X.D.; Chen, W.T.; Fu, D.F.; Zhang, H.; Teng, J.; Jiang, F.L. Microstructure, mechanical properties, and strengthening mechanisms of ultra-high strength Al–Zn–Mg–Cu alloy prepared by continuous extrusion forming process. Mat. Des. 2024, 242, 112985. [Google Scholar] [CrossRef]
  22. Lu, R.Q.; Zhang, L.; Zheng, S.W.; Fu, D.F.; Teng, J.; Chen, J.C.; Zhao, G.D.; Jiang, F.L.; Zhang, H. Microstructure, mechanical properties and deformation mechanisms of an Al-Mg alloy processed by the cyclical continuous expanded extrusion and drawing approach. Int. J. Min. Met. Mater. 2022, 29, 108–118. [Google Scholar] [CrossRef]
  23. Li, Q.L.; Huang, G.J.; Cao, Y.; Zhang, C.H.; He, J.; Jiang, H.A.; Lin, L.; Liu, Q. Microstructure refinement, strengthening and ductilization mechanisms in Al–Mg–Mn–Er–Zr alloy with high Mn content by friction stir processing. Mat. Charact. 2022, 189, 111939. [Google Scholar] [CrossRef]
  24. Liu, Y.; Liu, M.P.; Chen, X.F.; Cao, Y.; Roven, H.J.; Murashkin, M.; Valiev, R.Z.; Zhou, H. Effect of Mg on microstructure and mechanical properties of Al–Mg alloys produced by high pressure torsion. Scr. Mat. 2019, 159, 137–141. [Google Scholar] [CrossRef]
  25. Ciemiorek, M.; Chrominski, W.; Jasinski, C.; Lewandowska, M. Microstructural changes and formability of Al–Mg ultrafine-grained aluminum plates processed by multi-turn ECAP and upsetting. Mater. Sci. Eng. A 2022, 831, 142202. [Google Scholar] [CrossRef]
  26. Santos, I.C.D.; Mazzer, E.M.; Figueiredo, R.B.; Langdon, T.G.; Pereira, P.H.R. Evidence for two-stage hardening in an Al–Zn–Mg–Cu alloy processed by high-pressure torsion. J. Alloys Compd. 2023, 941, 168839. [Google Scholar] [CrossRef]
  27. Lee, S.W.; Yeh, J.W. Microstructural evolution and superplasticity of Al–5.8Mg–0.23Mn alloys processed by reciprocating extrusion. Metall. Mater. Trans. A 2005, 36, 2225–2234. [Google Scholar] [CrossRef]
  28. Yang, B.W.; Gao, M.Q.; Wang, Y.; Guan, R.G. Dynamic recrystallization behavior and mechanical properties response of rheo-extruded Al–Mg alloys with various Mg contents. Mater. Sci. Eng. A 2022, 849, 143450. [Google Scholar] [CrossRef]
  29. Yang, B.W.; Wang, Y.; Gao, M.Q.; Wang, C.F.; Guan, R.G. Microstructural evolution and strengthening mechanism of Al–Mg alloys with fine grains processed by accumulative continuous extrusion forming. J. Mater. Sci. Tech. 2022, 128, 195–204. [Google Scholar] [CrossRef]
  30. Kouhgard, M.; Daneshifar, M.H.; Jabbareh, M.A. Multipass friction stir welding of dissimilar Al–Si and Al–Mg cast aluminum alloys. Mater. Chem. Phys. 2024, 315, 128987. [Google Scholar] [CrossRef]
  31. Yan, K.; Chen, Z.W.; Lu, W.J.; Zhao, Y.N.; Le, W.; Naseem, S. Nucleation and growth of Al3Sc precipitates during isothermal aging of Al–0.55 wt% Sc alloy. Mat. Charact. 2021, 179, 111331. [Google Scholar] [CrossRef]
  32. Kishchik, M.S.; Mochugovskiy, A.G.; Cuda, M.; Kishchik, A.A.; Mikhaylovskaya, A.V. Particle stimulated nucleation effect for Al–Mg–Zr–Sc alloys with Ni addition during multidirectional forging. Metals 2023, 13, 1499. [Google Scholar] [CrossRef]
  33. Li, X.C.; Zhao, K.; Yang, L.Y.; Shi, S.Y.; Guo, E.Y.; Kang, H.J.; Hao, Z.G.; Chen, Z.N.; Wang, T.M. The role of TiB2 nanoparticles in reducing the microstructural sensitivity of as-cast Al–Mg–Mn alloy to cooling rate. Mater. Sci. Eng. A 2024, 894, 146157. [Google Scholar] [CrossRef]
  34. Zhu, Y.X.; Zhao, Y.; Chen, B. A study on Sc- and Zr-modified Al–Mg alloys processed by selective laser melting. Mater. Sci. Eng. A 2022, 833, 142516. [Google Scholar] [CrossRef]
  35. Dang, B.; Jian, Z.Y.; Xu, J.F. The effect of phosphorus on solidification behaviour of undercooled Al–70 wt.%Si alloys. Sci. Rep. 2020, 10, 18230. [Google Scholar] [CrossRef] [PubMed]
  36. Zheng, Q.J.; Zhang, L.L.; Jiang, H.X.; Zhao, J.Z.; He, J. Effect mechanisms of micro-alloying element La on microstructure and mechanical properties of hypoeutectic Al–Si alloys. J. Mater. Sci. Technol. 2020, 47, 142–151. [Google Scholar] [CrossRef]
  37. Luo, S.X.; Shi, Z.M.; Li, N.Y.; Lin, Y.M.; Liang, Y.H.; Zeng, Y.D. Crystallization inhibition and microstructure refinement of Al–5Fe alloys by addition of rare earth elements. J. Alloys Compd. 2019, 789, 90–99. [Google Scholar] [CrossRef]
  38. Saha, S.; Todorova, T.Z.; Zwanziger, J.W. Temperature dependent lattice misfit and coherency of Al3X (X = Sc, Zr, Ti and Nb) particles in an Al matrix. Acta. Mater. 2015, 89, 109–115. [Google Scholar] [CrossRef]
  39. Li, H.T.; Wang, Y.; Fan, Z. Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al–Mg alloys. Acta. Mater. 2012, 60, 1528–1537. [Google Scholar] [CrossRef]
  40. Guan, R.G.; Tie, D.; Li, Z.; An, Y.N.; Wang, X.; Li, Q.; Chen, X.B. Microstructure evolution and mechanical property improvement of aluminum alloys with high magnesium content during continuous rheo-extrusion. Mater. Sci. Eng. A 2018, 738, 31–37. [Google Scholar] [CrossRef]
  41. Shen, Y.F.; Guan, R.G.; Zhao, Z.Y.; Misra, R.D.K. Ultrafine-grained Al–0.2Sc–0.1Zr alloy: The mechanistic contribution of nano-sized precipitates on grain refinement during the novel process of accumulative continuous extrusion. Acta. Mater. 2015, 100, 247–255. [Google Scholar] [CrossRef]
  42. Liu, F.Z.; Zhu, X.H.; Qin, J.; Zhou, W.; Ling, J.Q.; Dong, Q.P.; Yu, J.M.; Nagaumi, H. Effect of Mn/Cr ratio on precipitation behaviors of α-Al(FeMnCr)Si dispersoids and mechanical properties of Al–Mg–Si–Cu alloys. Mater. Sci. Eng. A 2022, 860, 144269. [Google Scholar] [CrossRef]
  43. Malopheyev, S.; Kulitskiy, V.; Kaibyshev, R. Deformation structures and strengthening mechanisms in an Al–Mg–Sc–Zr alloy. J. Alloys Compd. 2017, 698, 957–966. [Google Scholar] [CrossRef]
  44. Zhang, M.T.; Jiang, T.; Xie, Y.F.; Feng, X.N.; Su, Y.; Shen, Z.K.; Sun, Z.G.; Xu, Y.X.; Li, W.Y. Microstructure evolution and strengthening mechanisms of an additive friction stir deposited multi-layer Al–Mg–Sc–Zr alloy. J. Alloys Compd. 2024, 1004, 175783. [Google Scholar] [CrossRef]
  45. Ouyang, Y.; Liu, F.; Chen, H.; Tao, X.; Du, Y.; He, Y. The structural stability, elastic constants and electronic structure of Al–Sr intermetallics by first-principles calculations. Phys. B 2011, 406, 3681–3686. [Google Scholar] [CrossRef]
  46. Jang, D.H.; Park, Y.B.; Kim, W.J. Significant strengthening in superlight Al–Mg alloy with an exceptionally large amount of Mg (13 wt%) after cold rolling. Mater. Sci. Eng. A 2019, 744, 36–44. [Google Scholar] [CrossRef]
  47. Oguocha, I.N.A.; Tiamiyu, A.A.; Rezaei, M.; Odeshi, A.G.; Szpunar, J.A. Experimental investigation of the dynamic impact responses of as-cast and homogenized A535 aluminum alloy. Mater. Sci. Eng. A 2020, 771, 138536. [Google Scholar] [CrossRef]
Metals 15 00054 g001
Figure 1. OM images and statistical average grain size result of the CREed AM alloys modified with different Sc additions: (a) AM alloy; (b) AM–0.1Sc alloy; (c) AM–0.3Sc alloy; (d) AM–0.5Sc alloy; (e) statistical average grain size result.
Figure 1. OM images and statistical average grain size result of the CREed AM alloys modified with different Sc additions: (a) AM alloy; (b) AM–0.1Sc alloy; (c) AM–0.3Sc alloy; (d) AM–0.5Sc alloy; (e) statistical average grain size result.
Metals 15 00054 g001
Metals 15 00054 g002
Figure 2. SEM micrographs and EDS results of the CREed AM(–0.5Sc) alloys: (a) AM alloy; (b) AM–0.5Sc alloy; (c) EDS results of point A marked in (a); (d) EDS results of point B marked in (b).
Figure 2. SEM micrographs and EDS results of the CREed AM(–0.5Sc) alloys: (a) AM alloy; (b) AM–0.5Sc alloy; (c) EDS results of point A marked in (a); (d) EDS results of point B marked in (b).
Metals 15 00054 g002
Metals 15 00054 g003
Figure 3. XRD analysis results of the CREed AM alloys with different Sc content.
Figure 3. XRD analysis results of the CREed AM alloys with different Sc content.
Metals 15 00054 g003
Metals 15 00054 g004
Figure 4. TEM micrographs of (a) the AM alloy and (b) the AM–0.5Sc alloy fabricated through CRE.
Figure 4. TEM micrographs of (a) the AM alloy and (b) the AM–0.5Sc alloy fabricated through CRE.
Metals 15 00054 g004
Metals 15 00054 g005
Figure 5. Engineering stress–strain curves of CREed AM alloys with different Sc additions.
Figure 5. Engineering stress–strain curves of CREed AM alloys with different Sc additions.
Metals 15 00054 g005
Table 1. Chemical compositions of the Al–5Mg–xSc alloys fabricated through CRE (in wt%).
Table 1. Chemical compositions of the Al–5Mg–xSc alloys fabricated through CRE (in wt%).
AlloyMgScAl
Al–5Mg (AM)4.94–Bal.
Al–5Mg–0.1Sc (AM–0.1Sc)4.970.09Bal.
Al–5Mg–0.3Sc (AM–0.3Sc)4.920.31Bal.
Al–5Mg–0.5Sc (AM–0.5Sc)4.960.47Bal.
Table 2. Tensile properties and hardness results of the AM alloys prepared through CRE and Sc modification.
Table 2. Tensile properties and hardness results of the AM alloys prepared through CRE and Sc modification.
AlloyUTS (MPa)YS (MPa)EL (%)Hardness (HV)
AM257.6 ± 1.799.8 ± 2.152.8 ± 4.269.8 ± 0.7
AM–0.1Sc331.3 ± 2.4133.5 ± 1.241.8 ± 1.1101.4 ± 1.5
AM–0.3Sc389.2 ± 3.9181.3 ± 3.232.0 ± 2.5126.5 ± 1.9
AM–0.5Sc456.4 ± 3.6220.1 ± 2.824.8 ± 1.9143.7 ± 2.2
Table 3. Physical meaning and values of the symbols utilized in the calculation Equations (7)–(10).
Table 3. Physical meaning and values of the symbols utilized in the calculation Equations (7)–(10).
SymbolDescriptionValuesUnitRef.
kSSConstant13.8MPa/(wt%)[43]
nConstant1-[43]
CMg solute content4.94/4.96wt%This work
kHPHall–Petch coefficient0.14MPa·m−0.5[44]
dAverage grain size52.6/2.4μmThis work
GShear modulus28.9GPa[45]
bBurgers vector0.286nm[23]
dspAverage diameter20.5nmThis work
fvVolume fraction0.065-This work
αConstant0.3-[29]
MMean orientation factor3.06-[29]
ρDislocation density1.32 × 1013/9.47 × 1013m−2This work
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Yang, B.; Liu, W.; Liu, X.; Yang, D.; Gao, M. Microstructure and Tensile Property Tailoring of Al–5Mg (wt%) Alloy Combined with Continuous Rheo-Extrusion and Sc Modification. Metals 2025, 15, 54. https://doi.org/10.3390/met15010054

AMA Style

Yang B, Liu W, Liu X, Yang D, Gao M. Microstructure and Tensile Property Tailoring of Al–5Mg (wt%) Alloy Combined with Continuous Rheo-Extrusion and Sc Modification. Metals. 2025; 15(1):54. https://doi.org/10.3390/met15010054

Chicago/Turabian Style

Yang, Bowei, Wenyue Liu, Xin Liu, Dalong Yang, and Minqiang Gao. 2025. "Microstructure and Tensile Property Tailoring of Al–5Mg (wt%) Alloy Combined with Continuous Rheo-Extrusion and Sc Modification" Metals 15, no. 1: 54. https://doi.org/10.3390/met15010054

APA Style

Yang, B., Liu, W., Liu, X., Yang, D., & Gao, M. (2025). Microstructure and Tensile Property Tailoring of Al–5Mg (wt%) Alloy Combined with Continuous Rheo-Extrusion and Sc Modification. Metals, 15(1), 54. https://doi.org/10.3390/met15010054

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop