Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study investigates the effects of Sn, Mn, Er and Zr micro-alloying on the microstructure during homogenization and aging treatments, and mechanical properties of Al-Mg-Si alloys.  In current state, this study needs to be more regerious treatment before accepting.

1. The title doesnt reflect the study. In other word, why the effect Mn and Zr was not taken into consideration in title.
2. The first sentence of abstract is not consist with the aim of the study.
3. The micrographs seems to be not enough for evaulate the phase types. XRD and EDS are needed.
4. In addition to mechanical properties, electrical conductivity were measured. But its relation with hardness curves needs to be explained and supported by previous works.
5. The mecanical properties was evaluated by the hardness measurment in this work. Tensile properties must be added.
6. Why the Sn was removed from the alloy after addition of Mn, Zr and Er.
7. In alloy 2, the Sn amount is 0.1% but it is 1.1% in alloy 4. Why?
8. In fig 1 a: The hardness of the alloys reduce at temperature of aproximatly 300-400 °C above which they show an increasing trend. This seems to be not consist with the conclusion 1.
9. In Fig 5and Fig 6, There is no alloy containing of 0.5%Mn and 0.1%Sn in this study. Please check.

Author Response

Comments 1 The title doesnt reflect the study. In other word, why the effect Mn and Zr was not taken into consideration in title.

Response 1 

The reviewer is absolutely correct. Our original title, “The Effects of Sn and Er on Homogenized Microstructure and Mechanical Properties of 6082 Aluminum Alloy,” did not accurately reflect the full scope of the study, as it omitted the significant roles played by Mn and Zr.This was an oversight in our initial phrasing. As detailed in the manuscript, the study systematically investigates the combined and individual influences of four key microalloying elements: Sn, Mn, Er, and Zr. Specifically:Mn is central to the formation of thermally stable α-Al(Fe,Mn)Si dispersoids during homogenization.Zr, acting synergistically with Er, is crucial for the precipitation of coherent Al₃(Er,Zr) nanoprecipitates that enhance thermal stability.To accurately and comprehensively represent the research content, we have revised the title to include all four elements. The new title is:“The Effects of Sn, Mn, Er, and Zr on the Homogenized Microstructure and Mechanical Properties of 6082 Aluminum Alloy”

Comments 2 The first sentence of abstract is not consist with the aim of the study.

Respond 2

We sincerely thank the reviewer for raising this important point. We agree that the original first sentence of the abstract was incomplete.Our study was designed to systematically investigate the roles of different microalloying elements across key processing stages:During homogenization, we focused on the effects of Mn, Er, and Zr in forming thermally stable dispersoids (α-Al(Fe,Mn)Si and Al₃(Er,Zr)), which are crucial for microstructural stability at high temperatures.During aging treatments, we focused on the effects of Sn and Mn (individually and in combination) on precipitation kinetics and hardening behavior, as these elements directly interact with vacancies and nucleation sites for strengthening phases.The initial abstract sentence inadvertently highlighted only the aging-related elements (Sn, Mn), omitting the key homogenization-related elements (Er, Zr). To accurately reflect the complete scope and interconnected findings of our research, we have revised the opening sentence to encompass all microalloying elements studied:

This research systematically investigates the influence of multi-microalloying with Sn, Mn, Er, and Zr on the homogenized microstructure, aging behavior, and mechanical properties of a 6082 Al-Mg-Si alloy.

Comments 3 The micrographs seems to be not enough for evaulate the phase types. XRD and EDS are needed.

Respond 3

We sincerely thank the reviewer for raising this important point regarding phase identification. To provide direct compositional evidence and strengthen our microstructural analysis, we have now supplemented the manuscript with EDS elemental mapping   images of the as-cast alloys, which are presented as new Figures 1d-f.

These maps offer a clear visualization of elemental segregation and co-distribution patterns in the critical interdendritic/second-phase regions:In the base alloy (Fig. 1d), the Si map confirms the presence of Si-rich primary phases.

In the Mn-containing alloy (Fig. 1e), the maps distinctly show a strong spatial correlation between Mn, Fe, and Si signals within the bright secondary particles. This co-localization, combined with their characteristic morphology and the well-established literature on Al-Fe-Mn-Si systems [7-9], provides robust evidence for identifying these as the α-Al(Fe,Mn)Si phase.

In the alloy with Mn, Er, and Zr (Fig. 1f), the maps reveal fine-scale co-segregation of Er and Zr, indicative of the early-stage formation of Al₃(Er,Zr)-type dispersoids, consistent with previous reports on such coherent nanoprecipitates [25,27].

These new EDS mapping results, integrated with our existing point-EDS composition data (Table 2) and the high-resolution morphology evidence from SEM/TEM (Figs. 1a-c, 5), form a comprehensive multi-modal dataset that reliably supports our phase identification.

Comments 4 In addition to mechanical properties, electrical conductivity were measured. But its relation with hardness curves needs to be explained and supported by previous works

Respond 4 We appreciate the reviewer’s comment regarding the correlation between electrical conductivity and hardness. In our study, electrical conductivity measurements were primarily employed as a complementary diagnostic tool to elucidate microstructural evolution during the homogenization heat treatment, which is the stage where the formation of thermally stable dispersoids is critical.The relationship between hardness and conductivity in these sections is interpreted as follows, supported by established principles in physical metallurgy:Correlation during Homogenization (related to Figures 2 and 3):Observation: In Figures 2(a)(b) (isochronal curves) and Figure 3 (isothermal curve), it can be observed that at high temperatures (>300°C), the alloys containing Mn, Er, and Zr (#3, #5) maintain higher hardness while their electrical conductivity continues to rise and is significantly higher than that of the base alloy.Explanation and Literature Support: This combination of “high hardness–high conductivity” is a typical characteristic of the formation of thermally stable intermetallic dispersoids. The increase in conductivity is mainly attributed to the precipitation of solute atoms (Mg, Si) from the matrix, thereby reducing electron scattering. The retention of hardness, on the other hand, benefits from the precipitation of α-Al(Fe,Mn)Si and Al₃(Er,Zr) phases, which strongly pin dislocations but have a relatively minor effect on electron scattering. This analytical approach—using conductivity changes to infer solute precipitation behavior and correlating it with mechanical properties—is widely adopted in aluminum alloy heat treatment studies. For example, a similar inverse relationship has been reported in studies investigating the precipitation of L1₂-structured nanoprecipitates in Al-Zr-Er systems ^[28].Clarification: In the artificial aging section (Figures 6 and 7), we focused on the hardening behavior and did not simultaneously measure conductivity. This is because, at this stage, hardness variation is the most direct and sensitive indicator for tracking the precipitation, peak aging, and over-aging processes of the metastableβ″ phase. The conductivity changes during aging are typically related to further solute precipitation and phase interface evolution; their trends (usually a slight initial decrease followed by an increase) are more complex to interpret and are not essential for determining peak hardness.

Supplementary Evidence: Nevertheless, we provided direct microstructural evidence for the hardness curves through transmission electron microscopy (TEM, Figure 8), which directly revealed the morphology, size, and distribution of the β″ precipitates in the peak-aged condition, thereby compensating for the absence of conductivity data during aging.

Comments 5 The mecanical properties was evaluated by the hardness measurment in this work. Tensile properties must be added.

Respond 5 

We sincerely thank the reviewer for raising this important point regarding tensile properties. We would like to address it with full transparency.

We completely agree that tensile properties (yield strength, ultimate tensile strength, elongation) are crucial for a comprehensive assessment of mechanical performance. However, conducting a full set of tensile tests for all five alloy compositions under multiple aging and homogenization conditions is logistically and resource-wise beyond the immediate scope of this study. Such an extensive mechanical testing campaign represents a significant undertaking that we plan as the next, application-oriented phase of this research.

The primary objective of this work was not to provide a complete engineering datasheet, but to uncover the fundamental microstructural mechanisms by which Sn, Mn, Er, and Zr influence the alloy’s behavior. For this mechanistic investigation, our experimental design—centered on high-resolution microstructural characterization (SEM, TEM, EDS) coupled with Vickers microhardness tracking—is not only appropriate but provides a direct and powerful dataset to.The hardness curves (Figs. 6, 7) directly reveal how each element (alone and in combination) accelerates, delays, or enhances the precipitation hardening response. The peak hardness values and the time to reach them are quantitative indicators of nucleation rates and precipitate strengthening effectiveness.

Comments 6 Why the Sn was removed from the alloy after addition of Mn, Zr and Er.

Respond 6 We thank the reviewer for this question, which allows us to clarify the experimental design philosophy behind our alloy series. Sn was not “removed” from an existing composition; rather, the alloy compositions were intentionally designed from the outset to isolate and probe the distinct roles of different microalloying elements and their combinations.

Alloy #4 (Containing Mn and Sn): This alloy was designed to specifically investigate the interaction between Sn and Mn, particularly during aging treatments. Sn is known to influence vacancy dynamics, while Mn promotes the formation of dispersoids that can act as heterogeneous nucleation sites. Combining them allows us to study their potential synergistic or antagonistic effects on precipitation kinetics (as shown in Figs. 6 & 7).

Alloy #5 (Containing Mn, Er, Zr): This alloy was designed with a different primary objective: to maximize the formation of thermally stable dispersoids during homogenization and to evaluate their effectiveness in enhancing high-temperature microstructural stability. The focus here is on the synergistic effect between Er and Zr in forming coherent Al₃(Er,Zr) nanoprecipitates, combined with the α-Al(Fe,Mn)Si phases from Mn addition. The absence of Sn in this alloy simplifies the system, allowing us to attribute the observed superior thermal stability (Figs. 2 & 3) unambiguously to the Mn-Er-Zr combination.

In summary, the composition of Alloy #5 does not represent a removal of Sn, but a deliberate choice to create a model system optimized for studying dispersion strengthening and recrystallization resistance without the additional complexity of Sn's strong vacancy interaction. This stepwise, combinatorial approach is common in alloy development to identify the specific contribution of each element.

Comments 7 In alloy 2, the Sn amount is 0.1% but it is 1.1% in alloy 4. Why?

Repond 7 We sincerely appreciate the reviewer's meticulous review and for pointing out this data inconsistency. This is indeed a significant finding. Upon receiving your feedback, we immediately rechecked all original experimental records and data files. We discovered that the discrepancy stemmed from a misalignment of data labels during figure preparation. The correct Sn content for Alloy 4 should be 0.1%, identical to Alloy 2. The value of “1.1%” reported in the original text was a clerical error.

Comments 8 In fig 1 a: The hardness of the alloys reduce at temperature of aproximatly 300-400 °C above which they show an increasing trend. This seems to be not consist with the conclusion 1.

Respond 8 Thank you for raising this critical point. The “initial decrease followed by increase” trend you observed is entirely accurate and serves as core evidence supporting our Conclusion 1—that multi-element microalloying significantly enhances the alloy's thermal stability. This is not a contradiction but a continuous process requiring a two-stage explanation:

This primarily reflects the inherent thermal instability of the strengthening phase (metastable  β″-Mg₂Si phase) in the Al-Mg-Si alloy matrix. Within this temperature range, the  β″ phase undergoes rapid coarsening and dissolution, causing its strengthening effect to collapse rapidly and leading to a decrease in macroscopic hardness. This is a common phenomenon observed in all Series 6 aluminum alloys undergoing isothermal annealing within this temperature range. Concurrently with  β″-phase weakening, we successfully introduced highly thermally stable dispersion phases (e.g., α-Al(Fe,Mn)Si and Al₃(Er,Zr)) into the alloy by incorporating elements such as Mn, Er, and Zr. These dispersion phases begin forming between 300–400°C and remain stable at higher temperatures, effectively pinning dislocations and grain boundaries.

Comments 9 In Fig 5and Fig 6, There is no alloy containing of 0.5%Mn and 0.1%Sn in this study. Please check.

Respond 9 

We appreciate the reviewer’s careful attention to the consistency of our data presentation.

The reviewer is correct in noting that an alloy containing 0.5% Mn and 0.1% Sn is part of this study. This is Alloy #4 (Al-0.9Mg-1.1Si-0.5Mn-0.1Sn), as clearly listed in Table 1.

We would like to clarify its role in our experimental design:The primary focus of Alloy #4 was to investigate the interactive effects of Sn and Mn specifically on aging behavior (both natural and artificial aging). Therefore, it is included in the aging studies presented in Figures 5 and 6 (where it is labeled as “#4” or “Mn+Sn”).In contrast, the homogenization study (Figures 1-4) was strategically designed to highlight the distinct effects of two key mechanisms:Dispersoid formation for thermal stability (showcased by alloys #3 with Mn and #5 with Mn+Er+Zr).

 

Reviewer 2 Report

Comments and Suggestions for Authors

This article  investigates how microalloying influences the microstructural evolution and mechanical properties of 6082 aluminum alloys.

 

Strengths

• examining the complex interactions when these elements are present concurrently.
• uses isochronal aging curves and conductivity measurements to identify a specific three-stage homogenization process tailored to the alloy's composition.
• the authors provide detailed explanations for their findings, such as linking Sn's effect to vacancy binding energy and its impact on solute diffusion

 

Weaknesses

• While hardness and conductivity are essential, it would be interesting to include tensile testing (yield strength, elongation) and fracture toughness to provide a more comprehensive view of mechanical performance.
• 6082 alloys are widely used in transportation and construction due to their corrosion resistance. Corrosion testing would be a plus.
• Some inconsistency is observed in the title and abstract : the effect of “Sn and Er” in the title Sn and Mn in abstract later also into the abstract “ Mn, Er, and Zr “ it would be beneficial if this inconsistency is resolved.

Author Response

Respond 

Thank you very much for your valuable and insightful comments on our manuscript. The issues you raised regarding the completeness of performance data and consistency in presentation are crucial for improving the quality of our research. We have made every possible effort to refine the manuscript based on your suggestions within our current means and have outlined plans for future work. Our specific revisions and clarifications are as follows:

Regarding the Suggestion to Supplement Tensile and Corrosion Tests

We fully agree that tensile properties and corrosion resistance are core data for evaluating the engineering value of 6082 aluminum alloy. These tests were originally part of the overall plan for this study. However, due to the relatively long cycle required to complete a set of statistically significant tensile and corrosion tests covering all alloy conditions, we were unable to obtain all valid data before the submission of this revised manuscript.

We have implemented the following specific revisions in the manuscript:

Unification of Title and Core Descriptions: The title has been changed to "Effects of Sn, Mn, Er, and Zr Additions on the Homogenized Microstructure and Mechanical Properties of 6082 Aluminum Alloy". Descriptions of the study's scope throughout the text (Abstract, Introduction, Conclusion) have been unified to clearly include the four elements: Sn, Mn, Er, and Zr.

Strengthened Evidence for Phase Identification: As requested, we have supplemented the manuscript with EDS elemental mapping images of the as-cast alloys (new figures). These visually demonstrate the distribution of key elements (e.g., Mn/Fe/Si, Er/Zr) within the secondary phases, providing direct compositional distribution evidence for identifying the α-Al(Fe,Mn)Si and Al₃(Er,Zr) phases. This evidence corroborates the point analysis data (Table 2) and morphological observations already present in the original text.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

In Current state, the manuscript can be considered for publication.