Influences of Cu Content on the Microstructure and Strengthening Mechanisms of Al-Mg-Si-xCu Alloys
Round 1
Reviewer 1 Report
The work submitted for review concerns an important topic. The article is very interesting and comprehensively describes the effect of Cu on the microstructure and properties of Al-Mg-Si-xCu alloys.
A few faults of editorial nature were observed:
line 23: 0.5 wt.% to 4.5 wt.%
line 35: at the end is a divided paragraph
line 40: as 0.1 wt.%
line 42: 0.2 to 1.5 wt.%
line 45: 37.5%
line 53: 0.3 wt.% and 0.6 wt.%
line 56-57: 1.48 wt% to 1.86 wt.%
line 62: 0.2-0.7 Cu wt.%
line 100: 440oC
line 114: HF (2 ml), HCl (3 ml), HNO3 (5 ml), and H2O (200 ml).
line 180: (at 165oC)
line 183: the record "14,400 min" is unclear. Maybe it would be better to write "14 400 min"
line 245: (165oC/360 min)
line: 248: (165oC/360 min)
line 260: (165oC/480 min)
line 284: (165oC/480 min)
line 287: (165oC/540 min)
line 289: (165oC/540 min)
line 306: (165oC/960 min)
line 339: (165oC/960 min)
line 353: (0.5 wt.%)
line 438: wt.%
line 470: 61.3 MPa
line 496: to 4.5 wt.%.
line 498: 4.0 wt.%
line 500: wt.%).
line 544: -1.6%, -9.1%, and -10.9%.
Author Response
Point 1: The work submitted for review concerns an important topic. The article is very interesting and comprehensively describes the effect of Cu on the microstructure and properties of Al-Mg-Si-xCu alloys.
A few faults of editorial nature were observed:
line 23: 0.5 wt.% to 4.5 wt.%
line 35: at the end is a divided paragraph
line 40: as 0.1 wt.%
line 42: 0.2 to 1.5 wt.%
line 45: 37.5%
line 53: 0.3 wt.% and 0.6 wt.%
line 56-57: 1.48 wt% to 1.86 wt.%
line 62: 0.2-0.7 Cu wt.%
line 100: 440oC
line 114: HF (2 ml), HCl (3 ml), HNO3 (5 ml), and H2O (200 ml).
line 180: (at 165oC)
line 183: the record "14,400 min" is unclear. Maybe it would be better to write "14 400 min"
line 245: (165oC/360 min)
line: 248: (165oC/360 min)
line 260: (165oC/480 min)
line 284: (165oC/480 min)
line 287: (165oC/540 min)
line 289: (165oC/540 min)
line 306: (165oC/960 min)
line 339: (165oC/960 min)
line 353: (0.5 wt.%)
line 438: wt.%
line 470: 61.3 MPa
line 496: to 4.5 wt.%.
line 498: 4.0 wt.%
line 500: wt.%).
line 544: -1.6%, -9.1%, and -10.9%.
Response 1: Thank you for your helpful comments! These mistakes have been corrected in the revised manuscript.
Reviewer 2 Report
The manuscript entitled: 'Influences of Cu content on the microstructure and strengthening mechanisms of Al-Mg-Si-xCu alloys' focuses on the effect of Cu on the Al-Si-Mg alloys, especially their precipitation and strengthening behaviors. In principle, the manuscript is nicely articulated. However, I have some minor comments that need to be addressed, before it may be accepted for publication.
- Representative tensile curves should be introduced, so that the readers may have an idea about the modulus, strength and ductility levels in a better fashion than just reading their values.
- XRD and/or EBSD patterns should be introduced so that the effect of crystallite size/grain size and/or texture in these materials can be studied. They are very important variable to be considered when dealing with the strengthening mechanisms.
Author Response
The manuscript entitled: 'Influences of Cu content on the microstructure and strengthening mechanisms of Al-Mg-Si-xCu alloys' focuses on the effect of Cu on the Al-Si-Mg alloys, especially their precipitation and strengthening behaviors. In principle, the manuscript is nicely articulated. However, I have some minor comments that need to be addressed, before it may be accepted for publication.
Point 1: Representative tensile curves should be introduced, so that the readers may have an idea about the modulus, strength and ductility levels in a better fashion than just reading their values.
Response 1: We appreciate the referee for this advice. The histograms of mechanical properties have been replaced by the tensile curves in the revised manuscript. In our study, it shows that either the Cu content or the aging treatment has little influence on the elastic modulus of aluminium alloy. This is in accordance with the results of previous studies (Metals 2016, 6, 43-55; Metals 2018, 8, 300-312).
Point 2: XRD and/or EBSD patterns should be introduced so that the effect of crystallite size/grain size and/or texture in these materials can be studied. They are very important variable to be considered when dealing with the strengthening mechanisms.
Response 2: We appreciate the modification suggestion. In the revised manuscript, the {200} pole figures of four as-quenched alloys have been added in which an evident fiber texture developed on the {200} planes is observed. This confirms that the recrystallisation is more pronounced in the alloy with a higher Cu content, since the {200} fibre texture is known to be a typical recrystallisation texture in aluminium alloys (Mater. Charact. 2014, 88, 111–118).
Author Response File: 
Author Response.pdf
Reviewer 3 Report
It is an interesting piece of work in microstructure/precipitate and mechanical properties relations in different Cu containing Al-Mg-Si alloys. There are some comments that the authors could consider as follows.
- What is the room temperature storage time? Have you considered the effect of room temperature storage time on the precipitation and the resultant strengthening mechanism? This question is because the results of hardness and mechanical properties are largely influenced by the room temperature storage time. E.g., in Figure 9, how long did it take after solution heat treatment in “as-quenched” condition?
- Do you have measured compositions?
- How did you measure grain size? Do you have any more concreate description more than “The grain size was statistically analysed using a JSM-7001F instrument.”?
- How about grain refiner additions in the materials? Also do you have any comments on grain growth during solutionzing?
- In Figure 3, “Rolling direction” means “Extrusion direction”?
Author Response
It is an interesting piece of work in microstructure/precipitate and mechanical properties relations in different Cu containing Al-Mg-Si alloys. There are some comments that the authors could consider as follows.
Point 1: What is the room temperature storage time? Have you considered the effect of room temperature storage time on the precipitation and the resultant strengthening mechanism? This question is because the results of hardness and mechanical properties are largely influenced by the room temperature storage time. E.g., in Figure 9, how long did it take after solution heat treatment in “as-quenched” condition?
Response 1: Sorry for this missing information. We have specified it in the “Experimental Methods” section of the revised manuscript. The artificial aging treatment of all samples in this study was undertaken immediately after quenching. Since the room-temperature storage time is extremely short (<30 s), its effect on the hardness and mechanical properties of alloys is not considered in the current work, but it will be investigated in our future work.
Point 2: Do you have measured compositions?
Response 2: Thank you for your helpful comments! The practical compositions of four alloys ingots were carefully examined after homogenization treatment, which were quite close to the nominal ones.
Point 3: How did you measure grain size? Do you have any more concreate description more than “The grain size was statistically analysed using a JSM-7001F instrument.”?
Response 3: Sorry for this missing information. In this study, the grain size was determined by a line intersection method according to ASTM E112-96, which involves an actual count of the number of grains intercepted by a test line. For each testing sample, at least 200 grains were considered. We have specified it in the “Experimental Methods” section of the revised manuscript.
Point 4: How about grain refiner additions in the materials? Also do you have any comments on grain growth during solutionzing?
Response 4: Thanks for pointing that out. In this study, a slight amount of Al-5%Ti-1%B was added during melting process as grain refiner. We have specified it in the “Experimental Methods” section of the revised manuscript. In order to focus on the copper content effect, the grain refiner effect on the microstructure and properties of alloys were not discussed in current work since the amounts of grain refiner are quite small and generally equal for all four alloys.
During solution treatment, on one hand, the coarse second-phase particles can act as nucleation sites for the recrystallised grains (e.g. particle-stimulated nucleation of recrystallisation (PSN)). On the other hand, these coarse second-phase particles can also exert a pinning force on the grain boundaries and thus limit the grain growth (Acta Mater. 1984, 32, 1407–1414). Therefore, the increasing amount of coarse second-phase particles led by Cu addition produced an obvious grain refinement effect.
Point 5: In Figure 3, “Rolling direction” means “Extrusion direction”?
Response 5: Thanks for pointing that out. This has been corrected in the revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The authors revised the manuscript according to reviewer's comments. The manuscript is recommended for publication.
