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Article

The Relationship Between Hardness and Microstructure in Zn/Mg Ratio-Controlled Al–Zn–Mg Alloys Aged at 120 °C

by
Wanlalak Sanphiboon
1,
Seungwon Lee
2,
Taiki Tsuchiya
2,
Abrar Ahmed
3,
Susumu Ikeno
2,
Tomoo Yoshida
1,4 and
Kenji Matsuda
2,3,*
1
Graduate School of Science and Engineering, University of Toyama, Toyama 930-8555, Japan
2
Faculty of Sustainable Design, University of Toyama, Toyama 930-8555, Japan
3
Advanced Aluminum International Research Center, University of Toyama, Toyama 930-8555, Japan
4
AISIN Keikinzoku Co., Ltd., Toyama 934-8588, Japan
*
Author to whom correspondence should be addressed.
Metals 2026, 16(3), 246; https://doi.org/10.3390/met16030246
Submission received: 23 January 2026 / Revised: 16 February 2026 / Accepted: 21 February 2026 / Published: 25 February 2026
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Abstract

Al–Zn–Mg alloys are widely recognized for their high strength-to-weight ratio, with the primary strengthening precipitates being the η/η′ and T/T′ phases. In this study, Al–Zn–Mg alloys with Zn/Mg molar ratios of 0.17, 0.40, 0.75, 1.3, 2.5, and 6.0 were systematically investigated after aging at 120 °C. η′/η precipitates predominantly strengthened alloys with high Zn/Mg ratios, whereas T′/T precipitates dominated those with low Zn/Mg ratios. In contrast, alloys with an intermediate Zn/Mg ratio (Zn/Mg ≈ 1.3) exhibited a balanced coexistence of η′/η and T′/T phases, resulting in the highest hardness among the six alloys. In addition, novel precipitates were observed, with their length increasing as the Zn/Mg ratio decreased. However, because these novel precipitates constitute only a small fraction of the total precipitate population, their direct contribution to the overall hardness remains unclear and warrants further investigation.

1. Introduction

Al–Zn–Mg series alloys are typical precipitation-hardenable aluminum alloys in which zinc is the principal alloying element, together with additions of magnesium. Owing to their excellent age-hardenability, high strength-to-weight ratio, good formability, and superior mechanical performance, these alloys are widely used as structural materials in aerospace, automotive, and other transportation applications [1,2,3,4]. The precipitation behavior of Al–Zn–Mg alloys is strongly influenced by the Zn/Mg ratio (in mol%). When the Zn/Mg ratio exceeds approximately 2, the formation of η′ and η phases is favored, whereas at lower Zn/Mg ratios, T′ and T phases are more likely to precipitate [5]. In our previous study [6], both high- and low-Zn/Mg Al–Zn–Mg alloys were aged at 120 °C and 200 °C to investigate the relationship between hardness and precipitate microstructure. The results showed that η′/η and T′/T phases formed preferentially in high- and low-Zn/Mg alloys, respectively. Moreover, novel precipitates were observed in low-Zn/Mg alloys aged at lower temperatures.
Based on previous studies [7,8,9,10,11,12,13], the precipitation behavior of Al–Zn–Mg alloys can be broadly classified into three practical regimes according to the Zn/Mg ratio. In Mg-rich alloys with low Zn/Mg ratios (~1.0–1.2 mol), T′/T-phase precipitation is favored. For example, Zhao et al. [8] reported that decreasing the Mg/Zn ratio significantly increases the number density of T′-Mg32(AlZnCu)49 precipitates. Similarly, Lee et al. [10] observed square-shaped T′ precipitates in the matrix of alloys with low Zn/Mg ratios, confirming the dominance of T′-phase precipitation in Mg-rich compositions. At intermediate Zn/Mg ratios (~1.3–1.8 mol), co-precipitation of T′ and η′ phases is commonly observed, leading to enhanced strengthening. Zou et al. [9] demonstrated that the coexistence of T′ and η′ precipitates with a high number density contributes to enhanced strengthening in this compositional range. In contrast, Zn-rich alloys with Zn/Mg ratios ≥ 2.0 mol% predominantly form η′/η (MgZn2-type) precipitates. For instance, Zou et al. [9] reported that η′ precipitation becomes dominant when the Zn/Mg ratio exceeds approximately 2.86. Representative examples reported in the literature include Zn/Mg ≈ 1.10 mol% for T′-dominated systems and Zn/Mg ≈ 2.13 mol% for η′-dominated, Zn-rich designs. In addition to the Zn/Mg ratio, the total solute content (Zn + Mg) plays a main role in determining the overall strength of Al–Zn–Mg alloys. Typical high-strength alloys are designed with Zn + Mg contents of approximately 6–7 mol%. For example, ultra-high-strength alloys often contain Zn + Mg ≈ 6.91 mol%, whereas T-phase-strengthened designs have been reported with Zn + Mg ≈ 6.23 mol%.
Although numerous studies have investigated Al–Zn–Mg alloys with various Zn/Mg ratios while maintaining the total Zn + Mg content near ~7 mol%, most of these investigations have been limited to relatively narrow compositional ranges or specific alloy systems. Consequently, a systematic and unified understanding of precipitation behavior across extremely low to extremely high Zn/Mg ratios under identical aging conditions remains lacking. To address this gap, the present study examines an exceptionally wide Zn/Mg ratio range (0.26, 0.40, 0.73, 1.3, 2.5, and 6.0), enabling a direct and comprehensive evaluation of the transition in precipitation behavior across distinct compositional regimes. Aging was performed at 120 °C, which is widely used as a peak-aging (T6) baseline temperature that promotes a fine, high number density of strengthening precipitates while suppressing rapid coarsening and over-aging effects that occur at higher temperatures [14,15,16]. This study aims to systematically investigate the age-hardening response and its relationship with the microstructure of precipitates—particularly the T′/T and η′/η phases—and to examine the characteristics of the novel precipitates in greater detail.

2. Materials and Methods

Six Al–Zn–Mg alloys were prepared from high-purity raw materials: aluminum (99.99%), zinc (99.9%), and magnesium (99.9%). Melting was carried out in atmospheric air, and the alloys were cast into a permanent steel mold. Each casting ingot was sectioned into top and bottom regions, and two measurement points were analyzed in each section. In total, four measurement points per alloy were evaluated, and the average values were calculated. The nominal chemical compositions are summarized in Table 1. Chemical analysis was performed using an Arc/Spark Optical Emission Spectrometer (OBLF QSN 750-II, Witten, Germany). Based on industry standards for spark optical emission spectroscopy (Spark OES) and considering OBLF systems as high-precision instruments, the estimated measurement accuracy for major aluminum alloying elements is approximately ±0.0005 to ±0.005 wt%. This uncertainty range is substantially smaller than the compositional differences among the designed alloys, indicating that the reported chemical compositions and Zn/Mg ratios are reliable and reproducible within experimental uncertainty. The alloys are designated as ZM16, ZM25, ZM34, ZM43, ZM52, and ZM61. The alloys consist of zinc (Zn) and magnesium (Mg), represented by ‘Z’ and ‘M’, respectively. The numbers, 1, 2, 3, 4, 5, and 6, and 6, 5, 4, 3, 2, and 1, correspond to the molar percentages and weight percentages of Zn and Mg. Thermodynamic phase predictions were performed using Thermo-Calc software (version 2024a, Thermo-Calc Software AB, Stockholm, Sweden), as shown in Figure 1 for the aging temperature of 120 °C. Based on the calculated phase diagrams, alloys with low Zn/Mg ratios (ZM16 and ZM25) are expected to preferentially form T-phase precipitates in the Al matrix. Alloys with Zn/Mg ratios close to unity (ZM34) are predicted to promote the formation of both T and η phases. In contrast, alloys with high Zn/Mg ratios (ZM43, ZM52, and ZM61) are expected to predominantly form η-phase precipitates in the Al matrix.
The as-cast ingots were homogenized at 450 °C for 24 h in an air furnace. Subsequently, the ingots were hot-extruded at approximately 400 °C into sheets with a thickness of ~1.5 mm and a width of ~15 mm, followed by cold rolling to a final thickness of 1.0 mm. The rolled sheets were cut with a size of 10 mm width and 10 mm length, and the solution was heat-treated at 475 °C for 60 min in an air furnace and immediately quenched into ice water (approximately 5 °C) to retain a supersaturated solid solution. Artificial aging treatments were conducted at 120 °C and 200 °C in a temperature-controlled silicone oil bath. Vickers microhardness measurements were performed using a Mitutoyo HM-101 hardness tester (Kawasaki, Japan) under a load of 9.8 N with a dwell time of 15 s. For each condition, hardness values were obtained from multiple indents and averaged. For Transmission electron microscopy (TEM) observations, aged alloy specimens were prepared from aged samples by mechanical grinding followed by electrolytic polishing. Transmission electron microscopy (TEM) specimens were prepared from aged samples by mechanical grinding followed by electrolytic polishing. Mechanical thinning was performed using silicon carbide (SiC) papers with grit sizes ranging from 320 to 2500 until the specimen thickness was reduced to approximately 0.10 μm. Initial electrolytic thinning was then carried out using a solution of 1/9 perchloric acid and 8/9 ethanol, reducing the thickness to approximately 0.08 μm. Further thinning before perforation was achieved by single-jet electrolytic polishing in a solution of 1/3 nitric acid and 2/3 methanol at room temperature (~25 °C). Final thinning to perforation was performed again using the 1/9 perchloric acid and 8/9 ethanol solution until a hole was formed. The resulting foils were cut into 3 mm diameter disks with a perforation at the center. TEM observations were conducted using a Topcon EM-002B microscope (Tokyo, Japan) operated at an accelerating voltage of 120 kV, and both high-resolution TEM (HRTEM) images and selected-area electron diffraction (SAED) patterns were acquired.

3. Results and Discussion

3.1. Vickers Microhardness

The Vickers microhardness results are presented in Figure 2. The alloys with different Zn/Mg ratios exhibit distinct hardness–aging behaviors, characterized by variations in hardening rate, peak hardness, and subsequent softening. During the early stages of aging, ZM52, ZM43, and ZM61 exhibited a more rapid increase in hardness. This behavior can be interpreted in light of the findings of Zhao et al. [8], who reported that a lower Mg/Zn ratio (i.e., a higher Zn/Mg ratio) enhances and accelerates the aging response through accelerating precipitate evolution and increasing the number density of precipitates. Accordingly, the higher Zn/Mg alloys in the present study are likely to promote the rapid formation of nanoscale strengthening features, such as GP zones, as well as the early nucleation of precipitates. These processes lead to a higher density of obstacles to dislocation motion at short aging times, resulting in a faster increase in hardness [11,17]. Nevertheless, further investigations are required to verify whether the present alloys strictly follow this mechanism quantitatively. ZM16 and ZM25 maintained nearly constant as-quenched hardness during the initial aging period, followed by a rapid increase to peak hardness and a subsequent decline. In contrast, ZM34 showed an immediate increase in hardness from the early stages of aging, reaching its peak more rapidly before decreasing. ZM43 exhibited a similar aging response to ZM34 but attained a higher overall hardness, achieving the highest peak hardness among all the alloys. ZM52 displayed higher hardness than ZM43 during the early aging stage; however, its hardening rate decreased before reaching peak aging, resulting in a lower peak hardness than both ZM43 and ZM34. Similarly, ZM61 showed a rapid increase in hardness at the early aging stage, followed by a pronounced deceleration in hardening and a plateau during intermediate aging. Consequently, the peak-aged hardness of ZM61 was lower than that of ZM16 and ZM25. The relationship between the Zn/Mg ratio and the difference between the peak-aged hardness and the as-quenched hardness, which represents the age-hardening ability of each alloy, is shown. As the Zn/Mg ratio increases from ZM16 (Zn/Mg = 0.26) to ZM43 (Zn/Mg = 1.3), the age-hardening ability increases continuously. However, a slight decrease is observed for ZM52 (Zn/Mg = 2.5), followed by a more pronounced reduction in ZM61 (Zn/Mg = 6.0). During the early stages of aging, distinct hardening behaviors are observed among alloys with different Zn/Mg ratios. These differences are consistent with previous studies and can be explained by variations in precipitation kinetics associated with alloy composition. Earlier investigations have demonstrated that the early-stage age-hardening response of Al–Zn–Mg(–Cu) alloys is strongly dependent on the Zn/Mg ratio. Yin et al. [18] reported that increasing the Zn/Mg ratio significantly accelerates the aging response and hardness evolution, whereas alloys with lower Zn/Mg ratios exhibit a delayed hardness increase during artificial aging, indicating slower precipitation kinetics in the initial stage.
This delayed hardening behavior is commonly manifested as a hardness plateau, which has been interpreted as an incubation period associated with the nucleation of strengthening precipitates. M.M. Shea et al. [19] showed that, in 7075 alloy, the early-stage hardness plateau corresponds to an incubation period for η′ nucleation, and that enhanced vacancy mobility (achieved via ultrasonic vibration) shortens this incubation period and accelerates age hardening. These findings suggest that higher Zn/Mg ratios promote faster formation of GP zones and η′ precipitates, thereby reducing the incubation time and leading to earlier peak aging. To further clarify the origin of the observed peak-aging behavior and to better understand precipitation hardening in Zn/Mg-controlled Al–Zn–Mg alloys, the microstructures of the alloys at their respective peak-aged conditions were examined by transmission electron microscopy (TEM).

3.2. TEM Observation

Representative bright-field TEM images and the corresponding selected area electron diffraction (SAED) patterns for all six alloys are shown in Figure 3. The orientation relationships, morphologies, and SAED spot positions of the precipitates were identified by comparison with previous studies [10,11,13,20,21,22,23,24,25]. Specifically, ZM16, ZM25, and ZM34 were examined along the (100)Al zone axis, whereas ZM43, ZM52, and ZM61 were observed along the (110)Al zone axis. Based on the TEM bright-field observations, the precipitate number densities for each alloy are summarized in Figure 4a as a function of the Zn/Mg ratio. The results show that the precipitate density remains nearly constant at low Zn/Mg ratios, increases sharply around Zn/Mg ≈ 1, and then reaches a plateau at Zn/Mg ≈ 2.5, remaining nearly unchanged up to Zn/Mg ≈ 6.0. In addition, the precipitate sizes can be classified into two distinct groups. ZM16 and ZM25 contain relatively coarse precipitates with sizes of approximately 16 and 6 nm, respectively, whereas ZM34, ZM43, and ZM52 exhibit finer precipitates with sizes of approximately 3 nm. Four types of microstructural features were identified: η′/η phases, T′/T phases, novel precipitates, and clusters that could not be classified based on known morphologies. The relationship between the Zn/Mg ratio and the fraction of identified precipitate types (η′/η phases, T′/T phases, and novel precipitates) is summarized in Figure 4b. The fraction of η′/η phases increases with Zn/Mg ratio up to approximately Zn/Mg ≈ 1.3 and then remains nearly constant up to Zn/Mg ≈ 6.0. In contrast, the fraction of T′/T phases exhibits an opposite trend, decreasing with increasing Zn/Mg ratio up to Zn/Mg ≈ 1.3 and remaining nearly unchanged thereafter. ZM16 and ZM25 exhibit similar selected area electron diffraction (SAED) patterns. In contrast, ZM34 shows noticeably stronger diffraction spots corresponding to the η′ phase than those observed in ZM16 and ZM25. ZM43 and ZM52 also present similar SAED patterns; however, ZM52 exhibits more pronounced η′-phase streaks than ZM43. These η′-phase streaks are not clearly observed in ZM61, which appears to show mostly diffraction spots associated with the η phase. Based on the SAED patterns of the η′/η phases, η′ phases are increasingly evident from ZM34 to ZM52, whereas in ZM61, the η′-phase streaks disappear and only η-phase spots are observed. Diffraction spots corresponding to the T′/T phases are observed in all alloys except ZM61. Notably, the observed orientation relationships are consistent with those reported for novel precipitates in previous studies [11]. These novel precipitates, aligned along the [110]Al and [110]Al directions, are observed only in alloys with Zn/Mg ratios below 1.0. Their fraction increases as the Zn/Mg ratio increases from 0.16 to 0.73, while their length increases with decreasing Zn/Mg ratio. However, because these novel precipitates account for only approximately 20% of the total precipitate population, their contribution to the overall hardness remains unclear and requires further investigation.
Based on the hardness measurements and TEM observations of precipitate size and number density, the age-hardening response increases with increasing precipitate density up to a Zn/Mg ratio of approximately 1.3, indicating a strong correlation between precipitate number density and age-hardening ability. In addition, the finer precipitates observed in ZM34, ZM43, and ZM52 are also likely to contribute to the enhanced age-hardening response, as finer precipitates are known to be more effective in increasing hardness [26,27].
According to the relationship shown in Figure 4b, the influence of precipitates on the age-hardening behavior can be classified into three major groups. ZM16 and ZM25 exhibit a high density of T′/T phases [28,29]. Although these two alloys show similar peak-aging hardness, differences are observed in their precipitate sizes and in the lengths of the novel precipitates. Despite the coarser precipitates in ZM16 compared with ZM25, their comparable peak hardness can be attributed to the higher calculated solid-solution strengthening in ZM16 [4,30,31,32]. ZM34 and ZM43 contain a balanced distribution of η′/η and T′/T phases [13,29]. The coexistence of η′/η and T′/T phases indicates co-precipitation, which is known to have a beneficial effect on hardness. In contrast, η′/η phases dominate in ZM52 and ZM61 [28,29]. Among all alloys, ZM61 exhibits the lowest peak-aging hardness. Based on the SAED patterns and bright-field TEM images, although ZM61 contains a large number of η phases (with a higher fraction of η than η′), its precipitates are relatively coarse, and its calculated solid-solution strengthening is lower than that of the other alloys [4,30,31,32]. As reported by Sato et al. [33], the solid-solution strengthening coefficients for Mg and Zn are approximately 25.2 and 6.3 MPa/√C, respectively, indicating that Zn contributes significantly less strengthening per atom than Mg. Consequently, the overall hardness of ZM61 is governed not only by precipitate density but also by the reduced solid-solution strengthening associated with its lower Mg content.

4. Conclusions

In conclusion, Al–Zn–Mg alloys with varying Zn/Mg ratios of 0.26 (ZM16), 0.40 (ZM25), 0.73 (ZM34), 1.3 (ZM43), 2.50 (ZM52), and 6.0 (ZM61) aged at 120 °C were investigated to clarify the effects of Zn/Mg ratio on precipitation behavior and hardness.
  • Vickers microhardness measurements show that the Zn/Mg ratio strongly governs the aging response and age-hardening ability of Al–Zn–Mg alloys. Higher Zn/Mg ratios (ZM43, ZM52, ZM61) result in faster initial hardening; however, the maximum peak hardness is achieved at an intermediate Zn/Mg ratio (ZM43, Zn/Mg = 1.3). At higher Zn/Mg ratios, the age-hardening ability decreases, particularly in ZM61, indicating the existence of an optimal Zn/Mg ratio for strengthening. Thus, although high Zn/Mg ratios accelerate early-stage hardening, excessive Zn/Mg leads to reduced peak hardness due to changes in precipitation behavior.
  • TEM observations at peak-aging conditions reveal that the precipitate number density is low at low Zn/Mg ratios, increases to a maximum around Zn/Mg ≈ 1.0, and then remains nearly unchanged at higher Zn/Mg ratios (≥2.5). Two distinct precipitate size regimes were identified: relatively coarse precipitates in ZM16 (~16 nm) and ZM25 (~6 nm), and finer precipitates in ZM34, ZM43, and ZM52 (~3 nm). With increasing Zn/Mg ratio, the fraction of η′/η phases increases up to Zn/Mg ≈ 1.3 and subsequently saturates, whereas the fraction of T′/T phases decreases correspondingly and remains nearly constant at higher Zn/Mg ratios.
  • The age-hardening response increases with increasing precipitate number density up to a Zn/Mg ratio of approximately 1.3 (ZM16, ZM25, ZM34, and ZM43), indicating a strong correlation between precipitate density and age-hardening ability. In addition, the finer precipitates observed in ZM34, ZM43, and ZM52 further contribute to enhanced hardening. The most pronounced age-hardening response is associated with the co-precipitation of η′/η and T′/T phases.
  • The novel precipitate aligned along [110]Al and [110]Al was observed only in alloys with Zn/Mg < 1.0. Their fraction increases as Zn/Mg increases from 0.16 to 0.73 (ZM16, ZM25, and ZM34). Their length increases with decreasing Zn/Mg ratio. These precipitates account for ~20% of the total precipitate population. Their contribution to overall hardness remains unclear and requires further investigation.

Author Contributions

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

Funding

A part of this research was supported by COI-NEXT, JST (JPMJPF2216).

Data Availability Statement

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

Acknowledgments

The authors thank the Advanced Aluminum International Research Center (ARC), University of Toyama.

Conflicts of Interest

Author Tomoo Yoshida was employed by the company AISIN Keikinzoku 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.

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Figure 1. Calculated isothermal section of the Al–Zn–Mg phase diagram at 120 °C using Thermo-Calc, showing the equilibrium phase regions.
Figure 1. Calculated isothermal section of the Al–Zn–Mg phase diagram at 120 °C using Thermo-Calc, showing the equilibrium phase regions.
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Figure 2. Variation of Vickers microhardness with aging time for Al–Zn–Mg alloys aged at 120 °C for ZM16, ZM25, ZM34, ZM43, ZM52, and ZM61.
Figure 2. Variation of Vickers microhardness with aging time for Al–Zn–Mg alloys aged at 120 °C for ZM16, ZM25, ZM34, ZM43, ZM52, and ZM61.
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Figure 3. The TEM bright field images, SAED pattern, and corresponding illustrated SAED pattern of (a–c) ZM16, (d–f) ZM25, (g–i) ZM34, (j–l) ZM43, (m–o) ZM52, and (p–r) ZM61, respectively.
Figure 3. The TEM bright field images, SAED pattern, and corresponding illustrated SAED pattern of (a–c) ZM16, (d–f) ZM25, (g–i) ZM34, (j–l) ZM43, (m–o) ZM52, and (p–r) ZM61, respectively.
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Figure 4. (a) Relationship between the Zn/Mg ratio and precipitate number density. (b) Relationship between the Zn/Mg ratio and the identified precipitate types.
Figure 4. (a) Relationship between the Zn/Mg ratio and precipitate number density. (b) Relationship between the Zn/Mg ratio and the identified precipitate types.
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Table 1. The chemical composition of the alloys.
Table 1. The chemical composition of the alloys.
Alloymol%wt%Al
ZnMgZn/MgZn + MgZnMgZn/MgZn + Mg
ZM161.495.820.267.313.465.110.678.58Bal.
ZM252.095.240.407.334.904.591.079.49Bal.
ZM342.974.090.737.066.913.521.9610.4Bal.
ZM434.173.291.277.469.642.803.4512.4Bal.
ZM524.781.892.536.6711.01.636.7412.6Bal.
ZM615.991.015.937.0013.40.8316.114.2Bal.
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MDPI and ACS Style

Sanphiboon, W.; Lee, S.; Tsuchiya, T.; Ahmed, A.; Ikeno, S.; Yoshida, T.; Matsuda, K. The Relationship Between Hardness and Microstructure in Zn/Mg Ratio-Controlled Al–Zn–Mg Alloys Aged at 120 °C. Metals 2026, 16, 246. https://doi.org/10.3390/met16030246

AMA Style

Sanphiboon W, Lee S, Tsuchiya T, Ahmed A, Ikeno S, Yoshida T, Matsuda K. The Relationship Between Hardness and Microstructure in Zn/Mg Ratio-Controlled Al–Zn–Mg Alloys Aged at 120 °C. Metals. 2026; 16(3):246. https://doi.org/10.3390/met16030246

Chicago/Turabian Style

Sanphiboon, Wanlalak, Seungwon Lee, Taiki Tsuchiya, Abrar Ahmed, Susumu Ikeno, Tomoo Yoshida, and Kenji Matsuda. 2026. "The Relationship Between Hardness and Microstructure in Zn/Mg Ratio-Controlled Al–Zn–Mg Alloys Aged at 120 °C" Metals 16, no. 3: 246. https://doi.org/10.3390/met16030246

APA Style

Sanphiboon, W., Lee, S., Tsuchiya, T., Ahmed, A., Ikeno, S., Yoshida, T., & Matsuda, K. (2026). The Relationship Between Hardness and Microstructure in Zn/Mg Ratio-Controlled Al–Zn–Mg Alloys Aged at 120 °C. Metals, 16(3), 246. https://doi.org/10.3390/met16030246

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