Current Progress in Rheoforming of Wrought Aluminum Alloys: A Review
Round 1
Reviewer 1 Report
The paper represents an interesting state of the art and is well done.
Author Response
Response: Thanks for your encouraging comments.
Reviewer 2 Report
This artice is dedicated to description of progress in rheoforming of aluminum alloys. This article was prepared very well and precisious. Authors used the 137 references for obtain the relevant review in this research field. The article is well organized and clearly described all parts of the review.
For my opinion, between the number and its unit must be inserted the space. For example 0.03 °C-1.
Units of the various values must be, for example, writen as: 20 min.°C-1, 28 mΩ.m-1, such it is writen on p. 11 (275 W.m-1.K-1).
Author Response
Response: Corrections according to the Reviewer’s comments have been made, as marked in red in the draft.
Reviewer 3 Report
Dear Authors,
The review paper aims at covering the last researches on rheoforming of wrought Al alloys, as clearly mentioned in the title. Despite this, I see that the discussion extensively presents also results regarding cast alloy. Furthermore, considering only wrought alloys, most results are relative to one alloy composition (7075 alloy), maximum two (7075 and 2024 alloy) and few others, as evident from table 2, Fig. 4,7-8, and from the manuscript. It appears that the selected topic is not wide enough to require that a review paper that is useful and effective for the reader is written. My suggestion is to focus on a topic that is more complex and wide and tailor the review paper in a different way.
In addition, as you also mentioned, numerous review papers are already available in scientific literature. At L. 57, 14 references are provided and 5 of them were published in the last 4 years). Therefore, it is not clear the reason for writing another review paper on the same topic.
You wrote “Recent rapid growth and intense desire in investigation on rheoforming of wrought Al 58 alloys have motivated this article.” (L. 58-59). I think this is not sufficient.
Finally, in Section 2. “Slurry Preparation of wrought Al alloys”, it appears that new results are discussed and presented in Fig 2-3. Since it is a review paper, it is supposed not to show new results.
Other:
Section 2. Why results for cast alloys are shown? It is suggested to better focus on the topic of the review, which is dedicated to wrought alloy, or to change the topic of the paper. 159-171: references to support the discussion should be provided and details regarding the process you are referring to should be added. Section 4. It is very interesting to show actual parts produced by rheoforming, but again this appears limited to two alloy compositions. Furthermore, no clear correlation between the properties of the components and the process is given. For instance, discussing the possibility to achieve very thin wall (proving values of thickness relative to the shown parts) in relation with globules size or other microstructural features.
Author Response
Reviewer 3:
I see that the discussion extensively presents also results regarding cast alloy. (Section 2. Why results for cast alloys are shown? It is suggested to better focus on the topic of the review, which is dedicated to wrought alloy, or to change the topic of the paper.)
Response: As the Reviewer mentioned, this paper includes some results for cast alloys in section 2 and 3. It is known that the alloys currently used in rheoforming processes are mainly conventional Al–Si casting alloys, such as A356, A357 and 319s. The researches on slurry preparation and rheoforming of these alloys are relatively mature. In section 2.1, we analyzed theoretically the possibility of slurry preparation of wrought alloys and compared their solidification characteristics with cast alloys, so that we added the data for cast alloys for the comparison. In section 2.2, we also compared differences of the slurries between wrought and cast alloys prepared by the same slurry preparation method, to present characteristics of the semi solid slurries of the wrought alloys.
Furthermore, considering only wrought alloys, most results are relative to one alloy composition (7075 alloy), maximum two (7075 and 2024 alloy) and few others, as evident from table 2, Fig. 4,7-8, and from the manuscript. It appears that the selected topic is not wide enough to require that a review paper that is useful and effective for the reader is written. My suggestion is to focus on a topic that is more complex and wide and tailor the review paper in a different way.
Response: As the Reviewer pointed out, many discussions in this paper are relative to 7075 and 2024 alloys. Regarding to the Reviewer’s suggestion, we have extended more data about other wrought alloys as shown in Table 2 (slurry preparation), Fig. 8 (tensile behavior) and the draft. After revision, this paper covers many candidate alloys, including 2xxx series (2014, 2024, 2017), 5xxx series (5052, 5083), 6xxx series (6061, 6063, 6082, 6201), 7xxx series (7075, 7050, 7A04 and 7A09). It should be noted that semi solid behavior and rheoforming of the 2024 and 7075 alloys are the most widely studied and results are published due to their good mechanical properties and easily accessible, so we presented and discussed more about these two alloys.
In addition, numerous review papers are already available in scientific literature. At L. 57, 14 references are provided and 5 of them were published in the last 4 years). Therefore, it is not clear the reason for writing another review paper on the same topic.
Response: The most studies and applications for semi solid processing have been done on Al-Si casting alloys. These Al-Si alloys have however limited strength and ductility. To develop further application of the semi solid processing, higher strength and ductility alloys are highly desirable [1]. This is the main purpose of this review publication. The most of the review papers up to now were mainly focusing on good castable Al-Si alloys. There are indeed some reviewes on wrought alloys, but lack of comprehensive reviews were reported. For example, in the 5 reviews published in last 4 years, ref [2] focused on the critical assessment of the materials for SSP, including Al alloys, Mg alloys and high temperature alloys; ref [3] reviewed the thixoforming of alloys; ref [4] was concentrated on the relationship of microstructure and properties of aluminum alloys (almost all of them are cast alloys) fabricated by SSP; ref [5] was similar to ref [4]; ref [6] was published very recently and it mainly presented the development and application of the SSP technology. Therefore, a review on the rheoforming of wrought alloys to show the current development and future trend of rheoforming of wrought alloys is valuable and interesting for wider industrial applications.
You wrote “Recent rapid growth and intense desire in investigation on rheoforming of wrought Al alloys have motivated this article.” (L. 58-59). I think this is not sufficient.
Response: We have made modification according to the Reviewer’s comments as:”This paper aims at reviewing the recent development of rheoforming of wrought aluminum alloys” and marked in blue in revised paper.
Finally, in Section 2. “Slurry Preparation of wrought Al alloys”, it appears that new results are discussed and presented in Fig 2-3. Since it is a review paper, it is supposed not to show new results.
Response: Agree with the Reviewer suggestion. Here is our misinterpretation or unclear description, the Fig. 2 and Fig. 3 actually are not new results. The content of Fig. 2, namely the liquid fraction curves for some common aluminum alloys employed in rheoforming, was used to demonstrate the difference of wrought and cast alloys. And it has been displayed in some other papers, such as ref [1]. The curves displayed in Fig. 2 were simulated by the latest software and maybe have some difference with previous versions. As for Fig. 3, the picture drew by the authors was a diagrammatic sketch of flow state in a thin channel of semi-solid slurry and liquid metal according to the opinion of Flemings [7] and Wannasion [8] etc, as stated in the L 194~200. Therefore, this has been rewritten.
“Others”:
L159-171: references to support the discussion should be provided and details regarding the process you are referring to should be added.
Response: We have corrected this part according to the Reviewer’s comments and marked in blue in the revised paper.
Section 4. It is very interesting to show actual parts produced by rheoforming, but again this appears limited to two alloy compositions. Furthermore, no clear correlation between the properties of the components and the process is given. For instance, discussing the possibility to achieve very thin wall (proving values of thickness relative to the shown parts) in relation with globules size or other microstructural features.
Response: As we mentioned in the paper, “in recent years, rheoforming of wrought Al alloys has attracted increasing interest and some progress has been achieved. However, the wrought Al parts produced by rheoforming are very limited. And almost all the parts were made by common 2024/6063/7075 alloys [9-14], so we presented and discussed more about these alloys. Considering the Reviewer’s suggestion, we have discussed the relationship between the properties of the actual parts and the rheoforming process in section 4.1 and 4.2.
Reference
1. Atkinson, H.V. Alloys for semi-solid processing. Solid State Phenom. 2013, 192, 16-27.
2. Rogal, Ł. Critical assessment: opportunities in developing semi-solid processing: aluminium, magnesium, and high-temperature alloys. Mater. Sci. Technol. 2017, 33, 759-764.
3. Czerwinski, F. Thermomechanical Processing of Metal Feedstock for Semisolid Forming: A Review. Metall. Mater. Trans. B 2018, 49, 3220-3257.
4. Pola, A.; Tocci, M.; Kapranos, P. Microstructure and Properties of Semi-Solid Aluminum Alloys: A Literature Review. Metals 2018, 8, 181.
5. Pola, A. Correlation between Microstructure and Properties of Semi-Solid Products. Solid State Phenom. 2019, 285, 12-23.
6. Kapranos, P. Current State of Semi-Solid Net-Shape Die Casting. Metals 2019, 9, 1301. 7. Flemings, M.C. Solidification processing. Metall. Trans. 1974, 5, 2121-2134.
8. Chucheep, T.; Wannasin, J.; Canyook, R.; Rattanochaikul, T.; Janudom, S.; Wisutmethangoon, S.; Flemings, M.C. Characterization of Flow Behavior of Semi-Solid Slurries with Low Solid Fractions. Metall. Mater. Trans. A 2013, 44A, 4754-4763.
9. Qi, M.; Kang, Y.; Zhou, B.; Liao, W.; Zhu, G.; Li, Y.; Li, W. A forced convection stirring process for Rheo-HPDC aluminum and magnesium alloys. J. Mater. Process. Technol. 2016, 234, 353-367.
10. Chen, G.; Yang, M.; Jin, Y.; Zhang, H.; Han, F.; Chen, Q.; Zhao, Z. Ultrasonic assisted squeeze casting of a wrought aluminum alloy. J. Mater. Process. Technol. 2019, 266, 19-25.
11. Wannasin, J. SSM slurry making process by GISS technology. In Proceedings of The 2nd International GISS Technology Forum., Shanghai, China.
12. Jarfors, A.E.W. Recent Advances in Commercial Application of the Rheometal Process in China and Europe. In Proceedings of 15th International conference on Semi-Solid Processing of Alloys and Composites, Shenzhen, China.
13. Moller, H.; Curle, U.A.; Masuku, E.P. Characterization of surface liquid segregation in SSM-HPDC aluminium alloys 7075, 2024, 6082 and A201. Trans. Nonferrous Met. Soc. China 2010, 20, Supplement 3, s847-s851.
14. Li, C.; Zhang, Z.F.; Fan, J. Applicaiton Research on Semi-solid Precision Forming Technology of High Strength Aluminum Alloy. Electro-Mechanical Engineering 2016, 32, 49-51.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 3 Report
Dear Authors,
thank you for your effort in revising the manuscript. I see your point in the answers to my concerns about the paper. I think the aim of the review paper now is clearer and the discussion of industrial application more complete.
My recommendation is to accept the paper in the present form.
