Improvement of Fatigue Strength in Additively Manufactured Aluminum Alloy AlSi10Mg via Submerged Laser Peening

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this study, fatigue properties of as-built PBF-LS/AlSi10Mg specimens treated by SLP using a fiber laser and/or a Nd:YAG laser with Q-switch were studied. XRD, SEM, profilometer and hardness tester were used to characterize the microstructures. It has been found that SLP using the fiber laser was laser treatment (LT) rather than laser cavitation peening (LCP). And the fatigue strength at N = 10⁷ was 85 MPa for LCP, and 103 MPa for combined process of blasting (B)+LT+LCP, whereas the fatigue strength of as-built specimen was 54 MPa. The review believes that this study is of interest to the community. There are some revisions necessary before this manuscript can be accepted for publication.

1. The quality of English should be improved. There are problems with sentence structure, verb tense, and clause construction, such as in 48 line, 49 line, 51 line, 52 line,56 line, 62 line, 68 line, 71 line, 73 line, 87 line, 172 line, 214 line, 247 line, 258 line,294 line,303 line and so on. In the manuscript, only one of the terms 'Figure' or 'Fig' should appear. The abbreviation should be clarified the first time it appears, and does not need to be explained again after the second occurrence such as 250 line and 259 line.

2. The figure in Figure 7 does not correspond to the caption. It requires revision.

3. The diagrams of the testing equipment used in this study are not necessary to include in the manuscript, such as Figure 6 and 7.

4. In 132 line, in Eq.1, what are the units of V_h and S_v?

5. Figure 9 (b) describes the relationship between time after irradiated pulsed laser t_L and sound pressure p_s. However, the manuscript only refers to the amplitude. Please explain the relationship between sound pressure p_s, amplitude, and LC-collapse impact.

6. From Figure 9, at t_w= 20 μs, the noise data corresponds to the video data. However, at t_w= 300 μs, the noise data doesn’t correspond to the video data. Please explain.

7. During SLP, sound pressure p_s using a Nd:YAG laser with Q-switch is two orders of magnitude higher than that using a fiber laser. Please explain it.

8. When observing the surface of the specimen with a digital microscope, was the surface of the specimen treated? If so, please provide a detailed description.

9. Figure 12 is very unclear, making it impossible to observe the microstructures, and it needs to be retaken. Additionally, some features in the image should be clearly marked.

10. In Figure 13, (e), (f) and (g) lack a scale and are unclear, and some features in the images need to be clearly marked such as partially melted particles, columnar structures and roughened edge. The narration in the manuscript does not correspond to the images, as they cannot be found within the figures. It can be seen from the images that there are a large number of circular defects in the microstructure, and the reasons for their formation need to be explained.

11. The combined process (B + LT + LCP) should clearly specify the order of each process. Please add more information.

12. According to the manuscript, the size of microstructures in specimens through LCP is the smallest. And from figure 12 and 13, microstructure defect is not found in specimens through LCP. However, the hardness and fatigue aren’t best. Please explain it.

Comments on the Quality of English Language

The quality of English should be improved.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Further annotations on Fig. 12 and Fig. 13 are needed to clarify the microstructure changes and phases. 

2. Please add ruler to all the images in Fig. 13. 

3. Can the authors add more results about the Fatigue test? such as the fatigue location/morphology. 

Comments on the Quality of English Language

Good.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Section 2: Please indicate how many samples were made and used for this effort. Discuss, where appropriate, how many replicates were used to produce the data that you are displaying. 

Figure 3: What was the window material used for liquid container?

Figure 4 and 5: you use the word Covex where it should be Convex. 

Figure 4 and 5: Please provide the laser beam diameter, the estimated focal spot size, and the beam quality of the laser output for each laser system. Also how many shots would you estimate that each area of the test coupon received for each system tested?

Figure 7: This image looks like an XRD machine, please update and clarify. 

Section 3.2 Line 306: Please provide a small description as to why one test piece would become concave or convex due to the induced surface stress and its potential benefits or drawbacks. 

Figure 13: some of your images are missing scale bars. 

Figure 14: What do the error bars represent? standard deviation? 95% confidence? please clarify. How many replicates went into each data point? How many test samples were used overall?

Figure 15: how many replicates were performed for each data point?

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The response address well on my suggestions.