# Development and Characterization of Cladding AISI 304L Stainless Steel on Aluminum

Yasmine Gabsi, Sahar Zouari, Mariem Abdennadher, Lamine Dieng, Riadh Elleuch

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Yasmine Gabsi, Sahar Zouari, Mariem Abdennadher, Lamine Dieng, Riadh Elleuch. Development and Characterization of Cladding AISI 304L Stainless Steel on Aluminum. Journal of Manufacturing and Materials Processing, 2025, 9 (17), pp.30. 10.3390/jmmp9020030. hal-04908898

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Article

# Development and Characterization of Cladding AISI 304L Stainless Steel on Aluminum

Yasmine Gabsi <fnref n="1" />,<fnref n="2" />, Sahar Zouari <fnref n="2" />, Mariem Abdennadher <fnref n="1" />, Lamine Dieng <fnref n="2" /> and Riadh Elleuch <fnref n="1" />,*

**Abstract:** The cladding process is a cost-effective solution to improve surface properties and obtain additional functionalities. The current paper focuses on the cladding of austenitic 304L stainless steel on aluminum substrate (SS/Al) by diffusion bonding, particularly relevant in the kitchenware field for safety issues. The study investigates the bonding characteristics and the deep drawing formability of the clad material, aiming to improve the understanding of its performance. The main results show a defect-free interface, as observed through microstructural analyzes. This highlights the ability of this process to create a good bond. The SEM/EDS results confirmed the absence of a diffusion layer. Microhardness and adhesion tests revealed non-uniform hardness values and moderate strength values across the interface. Numerical simulation showed the feasibility of deep drawing the SS/Al clad material without failure, proving its suitability in cookware manufacturing. These findings demonstrate the workability of diffusion bonding and suggest the potential for improving mechanical properties.

**Keywords:** aluminum; 304L stainless steel; cladding; interface; numerical modeling; deep drawing

Academic Editor: Antonio Ribeiro

Received: 24 December 2024

Revised: 20 January 2025

Accepted: 21 January 2025

Published: 23 January 2025

**Citation:** Gabsi, Y.; Zouari, S.; Abdennadher, M.; Dieng, L.; Elleuch, R. Development and Characterization of Cladding AISI 304L Stainless Steel on Aluminum. *J. Manuf. Mater. Process.* **2025**, *9*, 30. https://doi.org/10.3390/jmmp9020030

**Copyright:** © 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## 1. Introduction

Nowadays, scientific research in materials and manufacturing processes continually advances to produce materials with better mechanical and physicochemical properties. Clad metals, composed of two or more layers of different metals, have recently been developed and have gained significant industrial interest due to their ability to combine the beneficial properties of each material, such as good corrosion resistance, specific strength, and improved surface characteristics [1–3]. Many industries are interested in these clad materials to substitute the use of bulk material, particularly stainless steel clad plates. These latter have been used for various applications like pipelines [2], heat exchangers [3], shipbuilding [4], and particularly for kitchen utensils [5], where safety and performance are critical concerns [6]. Cooking pots, given their direct contact with daily consumed food, assume a crucial role in this context. In recent years, aluminum has been widely used in cookware manufacturing due to its light weight and high thermal conductivity. However, concerns regarding its potential health risks persist. Between 0.01% and 1% of orally ingested aluminum is absorbed by the gastrointestinal tract and is primarily eliminated by the kidneys [7]. This material serves as a competitive inhibitor of iron,

<footnote n="1">¹ Laboratory of Electromechanical Systems (LASEM), National School of Engineers of Sfax (ENIS), Sfax 3038, Tunisia; yasmine.gabsi@enis.tn or yasmine.gabsi2@univ-eiffel.fr (Y.G.); mariem.abdennadher@enis.tn (M.A.)</footnote>

<footnote n="2">² Laboratory of Metallic Structures and Cables (SMC), Gustave Eiffel University, 77420 Champs-sur-Marne, France; sahar.zouari@univ-eiffel.fr (S.Z.); lamine.dieng@univ-eiffel.fr (L.D.)</footnote>

<footnote>* Correspondence: riadh.elleuch@gnet.tn</footnote>
magnesium, and calcium and has been associated with conditions such as aluminum-induced osteomalacia, dialysis encephalopathy, and anemia [8]. High concentrations of aluminum have been discovered in the brain tissue of patients with Alzheimer's disease, dialysis encephalopathy, and Parkinson's disease [9]. In addition to health risks, strict regulations govern the materials used in cookware, emphasizing the importance of using safe and non-reactive materials for food contact. Therefore, adopting alternatives to aluminum is imperative. This initiative becomes especially important as concerns increase about the adverse effects of aluminum on health and the environment. Applying a non-toxic protective coating on aluminum may solve concerns regarding its direct contact with food while still benefiting from its positive properties. In this context, different kinds of coatings have been experimented on aluminum cookware since the 20th century. Each presents its own advantages and disadvantages. Among them, Teflon has been widely used due to its prominent non-stick properties [10,11]. Its ability to prevent food from sticking makes it convenient for cooking and cleaning. However, Teflon has raised concerns due to the potential release of toxic substances when overheated. At temperatures above 260 °C, Teflon begins to degrade, releasing PFOA (perfluorooctanoic acid) and other potentially harmful particles into the food and air. As a result, the need for a more robust solution has led to the development of cladding technologies, which involve bonding layers of different metals to create composite materials with better characteristics. In the context of cookware manufacturing, cladding stainless steel onto aluminum represents a promising solution.

The choice of the adequate cladding process has a crucial role in ensuring durability and product performance. Several cladding processes can be used to manufacture cookware. Each technique has its own advantages and specific limitations depending on the application.

Diffusion bonding is widely used due to its ability to create strong metallurgical bonds without the need for interlayers. This process involves heating the cladding materials under controlled temperature and pressure, allowing atomic diffusion at the interface to create a strong metallurgical bond [12,13]. This method ensures good adhesion and avoids the formation of intermetallic layers that can weaken the bond, thereby providing long-lasting performance even under thermal stress [1]. However, diffusion bonding requires precise control of temperature and pressure.

Hot roll bonding is another popular method, particularly used for producing large sheets of clad metals [14–16]. In this process, the cladding sheets are pressed together at high temperatures to create plastic deformation at the contact surface. While this technique allows for faster and more cost-effective production of flat cookware, it can result in lower bond strength than diffusion bonding. Additionally, pressure changes during the bonding process can lead to delamination.

Explosive welding is another option, using controlled explosions to bond dissimilar metals [17,18]. It is particularly advantageous for joining metals with very different properties. However, due to considerable energy demands and safety concerns, this technique is limited to industrial applications rather than consumer products like kitchenware.

Laser cladding is another promising technique, which uses a high energy laser beam to melt and then deposit a metallic powder layer onto a metallic substrate. According to the study of Zhang et al. [19], this method can assure good mechanical properties of cladded materials. In their study, this technique improves the microhardness of the bond interface over 2.5 times the substrate and the wear resistance, making it suitable for industrial applications subjected to severe conditions. However, laser cladding's main disadvantages are the thermal stresses, the equipment cost, and the need for control precision to avoid defects.

Table 1 summarizes the main advantages and limitations of these processes.
<table><caption>**Table 1.** Different cladding processes.</caption><thead><tr><th>Cladding Process</th><th>Bonding Quality</th><th>Advantages</th><th>Limitations</th><th>Applications</th><th>Ref</th></tr></thead><tbody><tr><td>Diffusion Bonding</td><td>Excellent</td><td>Strong metallurgical bond</td><td>Requires precise temperature and pressure control</td><td>Cookware (deep drawing)<br>Heat exchangers</td><td>[12,13]</td></tr><tr><td>Hot Rolling</td><td>Good</td><td>Fast<br>Large-scale production<br>Suitable for flat products</td><td>Weaker bond<br>Potential delamination</td><td>Flat cookware sheets<br>Automotive parts</td><td>[5,14–16]</td></tr><tr><td>Explosive Cladding</td><td>Very Good</td><td>No heating required</td><td>High energy Safety concerns<br>Expensive</td><td>Industrial applications<br>Shipbuilding</td><td>[17,18]</td></tr><tr><td>Laser Welding</td><td>Good</td><td>Improved wear resistance</td><td>High energy consultation<br>Cost of equipment<br>Thermal stresses and dissipation</td><td>Mechanical components subjected to severe friction and wear</td><td>[19]</td></tr></tbody></table>

Among the various cladding techniques, diffusion bonding stands out due to its ability to create a strong metallurgical bond without defects. However, its application for stainless steel and aluminum in the cookware field remains underexplored, presenting a novel focus for this research. Unlike traditional materials such as aluminum cookware or coated aluminum with Teflon or ceramic coatings, this study introduces a clad product of a thin layer of stainless steel onto aluminum that combines the high thermal characteristics of aluminum with the exothermic properties of stainless steel, used as a heating element in this kind of device. This solution reduces food contaminations risks during cooking as the stainless steel, a safe and inert material, is in direct contact with food.

To date, hot rolling is the most widely studied method for cookware manufacturing. Okui et al. [5] demonstrated the potential of the hot rolling technology to clad aluminum and stainless steel, which can be efficient for kitchenware application. However, the mechanical bond created by the hot rolling technique relies on plastic deformation, which can result in weak adhesion and increased risks of delamination. In contrast, the diffusion bonding adopted in this study, may provide a stronger bond at an atomic level [13], without the need for mechanical deformation and thus reducing the delamination risks.

In this study, the microstructure and the interface strength were analyzed. Numerical modeling is also applied to simulate the deep drawing of SS/Al clad plates, which are designed for cooking pot manufacturing. The first section of this paper presents the used cladding technique and the testing procedures, involving scanning electron microscopy (SEM) for the microstructural observations, an energy dispersive spectroscopy analysis (EDS), the strength tensile test to evaluate the bond strength and the deep drawing numerical modeling of SS/Al clad plate. The second section exhibits the main findings and a discussion on the results.

## 2. Materials and Methods

### 2.1. Hot Diffusion Bonding

#### 2.1.1. Process Description

Before cladding, both stainless steel and aluminum plates were carefully polished to ensure a clean surface without contaminants and to enhance the atom diffusion at the material interface. The cladding process began by carefully positioning the aluminum substrate above the stainless steel plate on a 5-ton manual hydraulic press (Figure 1). The top plate, made of aluminum, was then heated to a temperature below the aluminum
melting temperature, using a controlled blowtorch. Then, a pressure of 5 tons was applied to bond the two plates together. The raw plates of aluminum and 304L stainless steel measured 100 mm in length, 50 mm in width and were 2 mm and 1 mm thick, respectively. The chemical compositions of both materials are listed in Table 2. Considering the contact area of 5 × 10³ mm², the contact stress at the interface was approximately 10 MPa.

<figure><img src="image_2.png" /><figcaption>Figure 1. Hydraulic machine with a capacity of 5 tons.</figcaption></figure>

<table><caption>Table 2. Chemical composition of 304 L stainless steel and aluminum.</caption><thead><tr><th rowspan="2">Element<br>wt%</th><th rowspan="2">Si<br>0.207</th><th colspan="3">Aluminum 1050</th><th colspan="3">304L Stainless steel</th><th rowspan="2">Al<br>Balance</th></tr><tr><th>Fe<br>0.332</th><th>Cu<br>0.012</th><th>Mn<br>0.0017</th><th>Mg<br>0.012</th><th>V<br>0.013</th><th>Ti<br>0.014</th><th>Zn<br>0.012</th></tr></thead><tbody><tr><td>Element<br>wt%</td><td>C<br>0.023</td><td>Mn<br>1.43</td><td>Ni<br>8.05</td><td>Cr<br>18.47</td><td>Mo<br>0.089</td><td>Si<br>0.476</td><td>P<br>0.019</td><td>S<br>0.0002</td><td>Fe<br>Balance</td></tr></tbody></table>

### 2.1.2. Process Optimization

To optimize the cladding process, a series of tests were carried out under a constant pressure of 10 MPa and while varying the temperature to heat the aluminum material. Table 3 presents the selected temperature values.

Initially, the tests were performed within the temperature range recommended in the literature (60% to 90% of the lowest melting temperature of the cladding materials, which in this case is aluminum) [1]. However, the results were unsatisfactory, as the plates failed to bond effectively. As a result, the temperature was increased closer to the melting point, and at 650 °C, the aluminum and stainless steel plates successfully bonded.

<table><caption>Table 3. Cladding process parameters.</caption><thead><tr><th>Test</th><th>Temperature (°C)</th><th>Pressure (MPa)</th><th>Nature of Bonding</th></tr></thead><tbody><tr><td>1</td><td>450</td><td>10</td><td>No bonding</td></tr><tr><td>2</td><td>500</td><td>10</td><td>No bonding</td></tr><tr><td>3</td><td>550</td><td>10</td><td>No bonding</td></tr><tr><td>4</td><td>600</td><td>10</td><td>No bonding</td></tr><tr><td>5</td><td>630</td><td>10</td><td>Poor bonding</td></tr><tr><td>6</td><td>640</td><td>10</td><td>Poor bonding</td></tr><tr><td>7</td><td>650</td><td>10</td><td>Good bonding</td></tr></tbody></table>
## 2.2. Microstructural Observations

The microstructural characteristics of the clad interface were investigated using SEM (Hitachi SU5000 machine manufactured by Hitachi High-Tech Corporation in Tokyo, Japan), which provided high-resolution images to assess the quality of bonding between the stainless steel and aluminum plates. Prior to the microstructural observations, the samples were hot-mounted and then carefully polished using a Mecatech 250 SPC polisher manufactured by Presi in Eybens, France. To achieve a smooth and uniform surface. This critical step minimized surface roughness and eliminated potential contaminants, which could interfere with the microscopic analysis. To reveal the microstructure of each material, chemical etching was performed using specific acid mixtures. For the aluminum, a paste containing 20% of nitric acid (HNO$_3$), 5% of hydrofluoric acid (HF), and 75% of water, was applied. While the stainless steel was etched using a solution of 75% hydrochloric acid (HCl) and 25% nitric acid (HNO$_3$).

## 2.3. Microhardness Test

The microhardness test was conducted to evaluate the microhardness distribution across the interface of the clad materials, using a Vickers microhardness tester (HV 0.05). The study area is indicated in Figure 2, where the measurement grid is presented in green. Indentations were made along the cross-section to evaluate the bonding microhardness. This test, conducted according to DIN EN ISO 6507-1 standard [20], provides insights into the microhardness variations between the aluminum and stainless steel layers, which is important to understand the mechanical behavior of the clad material.

<figure><img src="image_3.png" /><figcaption>**Figure 2.** Measurement grid.</figcaption></figure>

## 2.4. Adhesion Test

Bond strength appeared as an important mechanical property that could affect the effective use of cladding. To establish a statistical average, three tensile tests were conducted on three clad pellets of 15 mm in diameter. The test was performed using a tensile testing machine with a maximum force capacity of 100 kN (SYNTIUM non-standard universal testing machine). The pellets are glued between metal cylinders of the same diameter using the ADEKIT A310-1 adhesive, a methacrylate adhesive frequently used for composite materials. The assembly is then mounted on the tensile machine. After applying a compressive force of 26 kN for 1 h, the assembly is then left at room temperature for 24 h before the mechanical test. The tensile test configuration is presented in Figure 3.
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Tensile test configuration.</figcaption></figure>

## 2.5. *Numerical Modeling*

In this part, numerical modeling using Abaqus Software is used to study the formability of the clad plate, which is a crucial property for cooking pot manufacturing. The cookware pots are manufactured by the deep drawing process; it is therefore essential to determine the forming limits of clad plates. Unlike a single sheet metal layer, clad sheets (two layers or sandwich) exhibit complex behavior during press forming [5]. The study focused on determining whether significant deformation and delamination occured in the cladding zone, as the two materials have different anisotropies. The shear in the cladding zone can significantly influence bonding integrity and overall deformation behavior, directly affecting the quality of the final product.

The forming limit curve (FLC) is the most wide failure criterion used in industries. FLC defines the degree of deformation (strain) that a sheet material can endure, depending on the mode of deformation, and illustrates the correlation between major and minor strain [21]. The FLC is determined experimentally and used to evaluate the forming limit diagram (FLD). Major strain occurs in the direction of the highest deformation, whereas minor strain is found in the direction of the lowest deformation [22]. For each mode of deformation, the limit is marked by the appearance of localized thinning (necking) or fracture [23]. The formability of a metal plate can be illustrated using the forming limit diagram (FLD). This diagram displays the critical strain levels that sheet metal can endure before failure, such as necking or fracturing, occurs. It offers a detailed view of the material's formability by plotting major strain against minor strain. By comparing these plotted strains to the material's forming limit curve (FLC), it helps to determine the present defects [24].

A numerical simulation of the deep drawing process is performed using Abaqus/Explicit. Due to symmetry conditions, one quarter of the setup has been modeled since we are looking at cylindrical deep drawing, as shown in Figure 4. The body dimensions used in the model are presented in Table 4. In the numerical model, the die and the blank holder were fixed. To simulate the material flow of the clad sheet, an elastic-plastic material model was defined in the numerical model using Abaqus and predefined von Mises equations with isotropic hardening. The yield stress and plastic strain values were obtained from experimental stress-strain curves [25,26], considering material anisotropy. Figure 5 presents the true plastic stress-strain curves used to define the plastic behavior of Al1050 and AISI 304L. These parameters were used to define the plastic behavior of the material. Furthermore, material properties such as density, Poisson's ratio, and Young's modulus were specified for both materials.
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Exploded view of the numerical simulation (Abaqus 6.13 Finite Element Software).</figcaption></figure>

<table><caption>**Table 4.** Tool dimensions.</caption><thead><tr><th colspan="2">Body</th><th>Dimensions (mm)</th></tr></thead><tbody><tr><td colspan="2">Clad plate radius</td><td>200</td></tr><tr><td rowspan="2">Punch</td><td>Radius</td><td>120</td></tr><tr><td>Corner radius</td><td>15</td></tr><tr><td rowspan="2">Die</td><td>Radius</td><td>111.2</td></tr><tr><td>Corner radius</td><td>12</td></tr><tr><td colspan="2">Gap (Punch-die)</td><td>8</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>**Figure 5.** Aluminum 1050 and AISI 304L true stress-strain curves [25,26].</figcaption></figure>

In addition, the rigid bodies, including the punch, die, and blank holder, were meshed with R3D4 surface elements. The 304L stainless steel and aluminum sheets were meshed with reduced integration shell elements (C3D8R), an eight-node element, in a deformable model. To determine the optimal mesh element size, a mesh convergence study was carried out based on experimental trial. The plates were meshed with elements of size 7 with a total of 2452 elements. The blank holder had larger mesh with 311 elements of size 14. To accurately capture critical stress and strain gradients, the die and punch radii had a fine element size of four. Bias meshing was applied along the edges to ensure a smooth transition in element size and alignment with the finer mesh near the radius. The die and punch had 1280 and 442 elements, respectively. Additionally, a holding force was applied on the blank holder. While there was a 1 mm gap between the stainless steel plate and the blank holder, the aluminum plate was in full contact with the die. Furthermore,
the contact between the rigid parts and the two plates was defined by surface-to-surface
contact with a coefficient of friction of 0.1, while tie constraint was used for the contact
between the two plates.

**3. Results and Discussions**

3.1. *Microstructural Analyzes*

The SEM observations, presented in Figure 6, reveal details regarding the interface between stainless steel and aluminum after the diffusion bonding process. Cross-section and longitudinal section observations (Figure 6a,b) exhibit a bonding between both materials, with no signs of separation or delamination. No visible defects such as cracks or pores have been observed. The interface between both materials suggests intimate contact and good adhesion.

<figure><img src="image_7.png" /><figcaption>**Figure 6.** SEM observations of the SS/Al clad plate interface. (a) Cross section; (b) Longitudinal section.</figcaption></figure>

The clad plate was etched to reveal the microstructure, as presented in Figure 7. The result indicates the presence of an austenitic grain structure with a ferrite grain boundary for the stainless steel [27]. The grain boundaries are visible, and the absence of significant inclusions or defects is confirmed. The aluminum microstructure reveals a typical dendritic grain structure with well-defined grain boundaries, represented by fine lines. The dark areas observed are likely associated with the presence of impurities within the aluminum. Despite being a highly pure alloy, it still contains few impurities or precipitates (such as Fe, Si), which may appear as small inclusions or dark areas. These impurities are often located at grain boundaries, further contributing to the observed dark regions.

<figure><img src="image_8.png" /><figcaption>**Figure 7.** Clad plate microstructure after etching.</figcaption></figure>
EDS analysis of the clad plate, as shown in Figure 8, provided additional information regarding the elemental distribution at the interface of the clad plate. The results revealed no sign of element migration (e.g., Fe, Ni, Cr) from the stainless steel to the aluminum. Thus, no diffusion layer was observed at the interface, which can be related to the short bonding time that might be insufficient and unable the additional elements to diffuse. However, carbon, being a small and active element, can diffuse quickly, especially at high temperatures, and was observed locally at the interface and within aluminum.

<figure><img src="image_9.png" /><figcaption>**Figure 8.** EDS analysis results.</figcaption></figure>
The EDS spectra, presented in Figure 9, provide the elemental composition on each side of the clad interface. The spectra display the typical composition of aluminum and stainless steel materials. However, both the EDS spectra and the elemental mapping results show traces of oxygen in both Al and SS, suggesting oxide formation. This may be due to the non-vacuum environment during the bonding process. These results contrast with other studies, which reported the formation of a diffusion layer at the interface after diffusion bonding [1,28]. To further optimize the quality of this clad plate, the cladding process should better perform in a vacuum environment to prevent oxide formation. Further optimization of the process parameters, particularly the bonding duration, is important to ensure the diffusion layer formation.

<figure><img src="image_10.png" /><figcaption>**Figure 9.** EDS spectra analysis: (a) Analyzed zones of the clad plate; (b) Spectra results.</figcaption></figure>

## 3.2. *Microhardness Results*

Figure 10 presents the microhardness test results, illustrating the variations in micro-hardness at the interface of the SS/Al clad material. The results show that the stainless steel layer exhibits significantly higher microhardness values, approximately 260 HV, in contrast to the aluminum layer, which has microhardness values of approximately 50 HV. Intermediate microhardness values are obtained at the bond interface, ranging from 133 HV to 270 HV. The minimum microhardness value at the interface represents approximately 50% of the stainless steel microhardness value and the double of Aluminum microhardness value. In contrast to the results reported by T. Vigraman et al. [28], the average microhardness value at the interface of 304L/low carbon steel was approximately 58% higher than the average hardness values of the base materials. This increase was due to
the presence of a diffusion layer at the interface. However, in the present study, the obtained microhardness values at the interface are not homogenous and remain below the average value of the clad material. This can be related to the absence of the diffusion layer or incomplete diffusion bonding.

<figure><img src="image_11.png" /><figcaption>**Figure 10.** Microhardness variation in the clad plate.</figcaption></figure>

### 3.3. *Bonding Strength*

Figure 11 presents force-displacement curves of the adhesion test for the three pellets named A, B, and C. For these samples, failure occurred at the adhesive-stainless steel interface. The curves illustrate the maximum rupture forces achieved for the pellets. For A, B, and C, rupture forces were 0.96 kN, 1.94 kN, and 1.19 kN, respectively. Since failure did not occur at the clad plate interface, the three samples could exhibit rupture forces greater than the average rupture force value of 1.37 ± 0.5 kN.

<figure><img src="image_12.png" /><figcaption>**Figure 11.** Strength-displacement curves of the adhesion test.</figcaption></figure>

This study represents an initial investigation of SS/Al diffusion bonding. The bonding parameters (e.g., temperature, pressure) were chosen based on preliminary tests to evaluate the feasibility of SS/Al diffusion bonding. Nevertheless, future work will focus on evaluating these parameters to further improve the mechanical performance of the final material.

### 3.4. *Deep Drawing Numerical Modeling*

The simulation of the deep drawing process for clad sheets serves as a critical tool for understanding the material behavior during forming. It allows the prediction of potential defects, such as wrinkling or tearing. Additionally, numerical simulation is used to optimize process parameters, such as blank holder force and punch speed, to enhance formability. Ultimately, this approach reduces the need for extensive experimental trials, saving
both time and costs, while contributing to developing and producing high-quality
cookware more efficiently.

The present study aims to verify the formability of the SS/Al clad plate. The forming limit diagram FLD was determined using Abaqus finite element analysis software and then compared with experimentally obtained forming limit curves of the same materials [29,30]. The results of the extracted major and minor strain were drawn into a scatter plot presented in Figure 12. If the equivalent strain value of the element is lower than the proposed FLC, the sample is formed without fracture. The points of the obtained forming limit diagram are well located in the safe zone under the FLC, indicating that the material can be formed without fracture, under the given conditions. Such results indicate that the clad plate is suitable for deep drawing application, such as cookware, and can undergo the forming process with the chosen parameters. It can also be seen that aluminum and stainless steel have almost the same forming behavior. This similarity in formability properties between both materials can provide insights into the quality of the cladding after deep drawing. Therefore, it will be interesting to determine the forming limit curve (FLC) of the clad plate to evaluate the formability of the assembly. Furthermore, the strain distribution on the clad plate during the deep drawing process was carried out (Figure 13). The results exhibit that the highest values of strain are concentrated at the edges of the radius facing the radius of the die and the wall of the deep-drawn part. This result can be explained by the high friction between the plate and the die corner, that causes localized deformation in this region because of the increase in the tensile strain. Furthermore, the tensile forces applied by the punch cause significant stretch of the wall of the deep drawn part. The localized thinning in these regions further intensifies the strain concentration, making them critical areas prone to potential failure, such as necking or tearing, if the material's formability limits are exceeded. Additionally, numerical results revealed a homogeneous strain distribution across both plates, with no excessive strain values observed in the cladding zone, as illustrated in Figure 13, indicating uniform deformation and well-maintained bond integrity throughout the process.

<figure><img src="image_13.png" /><figcaption>**Figure 12.** Forming limit diagram (FLD) of AISI 304L and Al 1050 plates.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>**Figure 13.** Strain distribution of the AISI 304L/Al 1050 clad plate.</figcaption></figure>

**4. Conclusions**

Cladding process by diffusion bonding was used to join an aluminum alloy and AISI 304L austenitic stainless steel plates. Based on microstructural analyzes, adhesion tests, microhardness test, and numerical modeling, several conclusions can be drawn:

* SEM analysis revealed a continuous interface between the aluminum and 304L stainless steel, free of pores or cracks.

* EDS results confirmed oxide formation and the absence of a diffusion layer, likely due to the use of a non-vacuum environment and insufficient bonding duration, respectively.

* The adhesion test results estimate a rupture force higher than 1.37 kN.

* Microhardness measurements obtained at the interface of the clad were non-homogeneous, indicating non-uniform bonding.

* The results of the numerical study validated the formability of the clad plate with a deep drawing process and underline the importance of optimizing the simulation to have a clear perspective about the formability of the SS/Al clad plate.

The current SS/Al cladding process demonstrates promoting bonding results, but requires improvements to ameliorate the bonding quality. Working under vacuum conditions is recommended to avoid oxide formation and further parameter optimization like pressure, temperature and bonding time is necessary to ensure better cladding performance.

**Author Contributions:** Conceptualization, Y.G., S.Z., M.A., L.D., and R.E.; methodology, Y.G., S.Z., M.A., L.D., and R.E.; software, M.A.; Validation, S.Z., L.D., and R.E.; formal analysis, Y.G., S.Z., and M.A.; investigation, Y.G., S.Z., M.A., L.D., and R.E.; data curation, Y.G. and M.A.; writing—original draft preparation, Y.G., S.Z., and M.A.; writing—review and editing, Y.G., S.Z., M.A., L.D., and R.E.; supervision, S.Z., L.D., and R.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** The raw data supporting the conclusion of this article will be made available by the authors on request.
**Acknowledgments:** The authors would like to thank Jean François David of SMC (Gustave Eiffel University) for his assistance during the adhesion tests and Christelle Herbin (Gustave Eiffel University) for her support in carrying out the hardness mappings.

**Conflicts of Interest:** The authors declare no conflict of interest.

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