Vacuum Diffusion Bonding Process Optimization for the Lap Shear Strength of 7B04 Aluminum Alloy Joints with a 7075 Aluminum Alloy Powder Interlayer Using the Response Surface Method
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReviewer comments Manuscript ID: metals-3911424
For lap welding of high-strength aluminum alloy 7B04 used in aircraft structures, it is proposed to use aluminum alloy 7075 powder as an intermediate layer to strengthen the vacuum-diffusion joint. Before welding, plasma activation surface treatment was applied. Joint and shear strength tests were conducted. The effects of temperature, pressure, and holding time on the LSS of the joint were investigated based on the response surface method. A quadratic regression model was developed. The technological parameters of the diffusion welding process were optimized. Experimental results confirmed that the error between the measured and predicted shear stress values ​​is approximately 5%, and the highest shear stress value of 174 MPa was achieved at 515 °C - 7.5 h - 4.4 MPa.
The article is interesting and can be accepted after minor revisions (correction of minor methodological errors and editing of the text).
- Error in numbering of points.
«l2.3. Diffusion Bonding Experiment»
Response 1:
- It is necessary to justify in more detail the choice of ranges of change of factors (Temperature (°C), Time (h), Pressure (MPa)) and indicate the accuracy of their measurement.
Response 2:
- The text indicates (Lines 189 and 190): «The DB process parameters range is defined as
temperature: 450- 530 °C,
pressure: 2-5 MPa,
and time: 1-10 hours.
Table 2 indicates:
«Table 2. Factors and their levels for DB experiment of 7B04 with a 7075 powder interlayer.
Parameter Unit Notation Levels –21/2 –1 0 1 21/2
Temperature °C T 450 462 490 518 530
Pressure MPa P 1 2.3 5.5 8.7 10
Time h t 2 2.4 3.5 4.6 5»
Need to explain how to do it correctly?
Response 3:
- “Table 3. CCD matrix and LSS results of DB experiment of 7B04 with a 7075 powder interlayer.”
Here is the matrix of the central composite design (CCD) method – 15 experiments.
Traditionally, the central composite design (CCD) method for three factors contains a full-factorial experiment of 23=8 experiments; 6 experiments – at star points with a shoulder of 1.414; 2–3 experiments in the center of the plan (total number – 16 or 17 experiments). In the reviewed article: 4 – experiments (Sr. No. 1–4); 6 experiments – at star points with a shoulder of 1.414 (Sr. No. 5–10); 5 – experiments in the center of the plan (total number – 15 experiments)
It is not clear why during the planning of the experiment, experiments were not conducted at the top level: +1 of all factors (Temperature (°C) Time (h) Pressure (MPa).
It is necessary to explain.
Response 4:
- “Figure 2. Dimensions of LSS test specimens.” it is necessary to justify the choice of the overlap area 1.4x8 mm.
Response 5:
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author reports a study on the diffusion bonding process applied to two 7B04 aluminum alloy sheets with 7075 aluminum alloy powder placed at the bonding interface.
The work is somewhat meticulous. For example, the author states that "Figure 1 shows the assembly of 7B04 sheets and 7075 powder," but I'm not sure what the sample sizes are.
From Figure 2, "The non-standard LSS specimen was designed as shown in Figure 2," I'll assume that's the sample size for welding. This means the overlap length is 1.4 mm. This seems too short to me. A small error in positioning will translate into a huge error in shear strength. I'd like to see what effect this overlap length had on strength.
I don't think this article brings anything new. There's a lot of literature on the diffusion bonding of aluminum alloys, including the one presented here.
Minor nitpicking:
The manuscript confuses the terms shear strength and tensile strength. For example, reference 16 was shear testing, so when the author writes on line 77, "Huang et al. [16] reported a tensile strength of 303-318 MPa for hot-rolled AA7075 at the optimal bonding conditions," it actually refers to shear strength. Furthermore, these authors [16] have published another article that is practically identical (Diffusion bonding of superplastic 7075 aluminum alloy), which today would certainly be considered plagiarism. I think this is not a good reference.
On line 433, it states that "The tested shear strengths of the base metal are 142 MPa and 130 MPa." This is incomprehensible.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author has adequately answered all my questions, so I accept the manuscript as is.
