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http://j urnal. unmer.ac.id /index .p h p/jtmt
T R A N S M I S I
ISSN (print): 9-772580-228020 ISSN (online): 2580-2283
Morphology Study of The Corrosion Rate on Weld Joint of Double Side Friction Stir Welding Aluminum Alloy AA6061
Simonne Andrean Crisdion
a, Poppy Puspitasari
a,b*, Avita Ayu Permanasari
a, Danang Priyasudana
a, Diki Dwi Pramono
a,b, Majid Niaz Akhtar
ca Department of Mechanical and Industrial Engineering, Universitas Negeri Malang, 65145, Indonesia
b Centre of Advanced Materials and Renewable Energy, Universitas Negeri Malang, 65145, Indonesia
cPhysics Department, The Islamic University of Bahawalpur, Pakistan
*Corresponding author email: [email protected]
A R T I C L E
I N F O R M A T I O N A B S T R A C T Received: 19 February 2023
Revised: 1 March 2023 Accepted: 7 March 2023 Published: 15 March 2023
The purpose of this study is to experimentally analyze the main causes of failure of AA6061 DSFSW joints based on welding temperature, weld defects, microstructure, corrosion rate and morphology of the corroded surface. Temperature testing using thermocouple to analyze the temperature, welding joint defects using DSLR camera and radiography test, microstructure using optical microscope, corrosion rate using AUTOLAB PGSTAT and morphology of corroded surface using SEM. The temperature analysis results show that the advancing side has a higher temperature than the retreating side, due to friction between the tool and base metal accompanied by the opposite welding direction. Visual inspection shows that all specimens and welding positions produce flash that is quite rough on the top (1G) and bottom (4G) surfaces and radiographic test results show incomplete fusion in 4 specimens.
Microstructure shows a change in shape and size resulting in recrystallization in the form of fine grains. The highest corrosion rate is found in specimen B 1G welding position of 0.63856mm/year and the lowest corrosion rate in specimen A of 0.058567mm/year. SEM test results show the type of corrosion that occurs in DSFSW welding joints is pitting corrosion.
Keywords: DSFSW, Morphology Corrosion Rate
A B S T R A K
DOI: 10.26905/jtmt.v19i1.9636
Tujuan dari penelitian ini adalah untuk menganalisis penyebab utama kegagalan sambungan DSFSW AA6061 berdasarkan temperatur pengelasan, cacat las, struktur mikro, laju korosi, dan morfologi permukaan yang terkorosi. Pengujian temperatur menggunakan termokopel, cacat sambungan menggunakan kamera DSLR dan uji radiografi, struktur mikro menggunakan mikroskop optik, laju korosi menggunakan AUTOLAB PGSTAT dan morfologi permukaan yang terkorosi menggunakan SEM. Hasil analisis temperatur menunjukkan bahwa advancing side memiliki temperatur yang lebih tinggi dibandingkan dengan retreating side, karena pengaruh arah pengelasan yang berlawanan. Inspeksi visual menunjukkan bahwa semua spesimen menghasilkan flash yang cukup kasar, dan hasil uji radiografi menunjukkan adanya Incomplete Fusion. Struktur mikro menunjukkan adanya perubahan bentuk dan ukuran yang mengakibatkan terjadinya rekristalisasi butiran halus. Laju korosi tertinggi terdapat pada spesimen B posisi pengelasan 1G sebesar 0.63856mm/tahun dan laju korosi terendah pada spesimen A sebesar 0.058567mm/tahun. Hasil uji SEM menunjukkan jenis korosi yang terjadi pada sambungan las DSFSW adalah korosi sumuran.
Kata Kunci: DSFSW, Morfologi Laju Korosi
2023 Unmer. All rights reserved
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1. IntroductionDefects are one of the failures in the fabrication process [1]. The defect trigger needs to be researched and investigated by analyzing the failure [2]. Failure analysis was critical in detecting the start of failure and its prevention [3]. Determining failure triggers can be done through laboratory observation, inspection, and also sample testing [4][2].
Appropriate analysis can reduce or prevent failures in the fabrication of a product or component [5]. The welding fabrication process cannot be separated from defects and failures, because of its usefulness in connected two specimens [6]. One type of the welding that is starting to become a research trend is Friction Stir Welding (FSW).
FSW, or friction stir welding, is a technique for joining specimens with various metal shapes [7].
FSW also has flaws, some of which being the welding process's lack of flexibility currently, FSW is only done on one side of the welded plate, therefore it cannot be applied to thick materials, and even if it can, the material must be flipped over [8].
Cox et al., (2014) successfully devised in his research, where the plate to be connected encounters friction from two chisels on opposing sides. DSFSW joints can have more strength than single-sided FSW joints because the stirring action is thoroughly blended [10].
The working principle of this welding utilizes the friction of the tool rotation with the workpiece which generates heat until the metal softens [11][12]. The corrosion rate is further affected by high heat created by friction and non-uniform cooling rates; this heat produces metallurgical transformations to across Heat Affected Zone (HAZ) and Weld Metal (WM) sectors [13][14], and can cause defects such as porosity, kissing bond, cracks, cavities (welding penetration), and flash and changes in microstructure [15]. The microstructure changes in welded joints can affect the resistance of welded joints to corrosion.
Corrosions cause damage to a material as a result of a chemical or electrochemical reaction between the material and its environment, usually the constituent metal alloy and its quality [16][17].
Corrosion can occur quickly if environmental control and prevention are not done properly [18].
Attempts are currently being made today to limit material damage produced by the manufacturing
process, so that the corrosion rate is kept as low as feasible and does not surpass the metal's economic worth, or before the metal gets damaged [19]. This corrosion has a major impact on the performance of welded joints [20]. Siddesh Kumar et al., (2022) dan Balaji Naik et al., (2019) in their research stated the importance of welding parameters to obtain joints that have resistance to corrosion rates. The study of welding joint failures is important to obtain good quality joints that can function optimally. The purpose of this study is to identify the morphology of the corrosion rate of Double Side Friction Stir Welding joints on Aluminum Alloys 6061-T6.
Figure 1. Illustration DSFSW process
2. Materials and Methods
2.1. Materials
The material used in this study is Aluminum Alloy 6061 series. The chemical composition of the specimen can be seen in Table 1.
Table 1. AA6061 Chemical Formulation
Compo
sition Al Si Cu Fe Mn Mg Ti Zn Other
% 95,8-
98,6 0,4-
0,8 0,15-
0,4 0,7 0,15 0,8-
1,2 0,15 0,25 0,05
Figure 2. depict the workpiece’s dimensions and cutting the plate using a saw.
Figure 2. DSFSW Specimen Dimensions
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2.2. Methodology of Research2.2.1 Welding Temperature
The temperature during the welding process is measured using a thermocouple integrated with Arduino Mega to display the temperature in degrees Celsius against time and welding direction.
2.2.2 Visual Inspection
To maintain test data, drawing designs, visual presentations utilizing written words, or shooting pictures or films of the recorded surface conditions are used instead of tools.
2.2.3 Radiography Test
Non-destructive testing of joint defects using radiography tests based on ASTM-E1032 standard practice for radiographic examination of weldments using industrial A-ray film.
2.2.4 Microstructure
Microstructure testing is conducted to determine changes in grain shape, grain size, joint properties, and phase using an optical microscope. Observations were made on the weld metal part of the welding joint.
2.2.5 Corrosion Rate
This same rate of corrosion was tested and used the electrochemical method with three electrode cells and a Potentiostat integrated with NOVA Software based on ASTM G102 Establishing for Measurement of Corrosion Rates and Related Data from Electrochemical Measurements as shown in Figure 2.2. This corrosion test utilizes a chemical substance as just an alternate for seawater with a sanitary 3.5% NaCl as shown in Figure 3.
Figure 3. Dimensions of Corrosion Testing Specimens An electrochemical technique is a way of measuring the corrosion rate by measuring the potential difference of the item in order to acquire the corrosion rate that happens; this approach measures the corrosion rate only when the rate is assessed over a lengthy period of time. The benefit of this approach is that we can quickly determine the corrosion rate when it is measured, therefore the measurement period is short. Testing the corrosion rate by electrochemical methods with polarization of
the free corrosion potential can be calculated using a formula based on Faraday's Law as below.
Where:
K = Constanta (0,129m/years or 0,00327mm/years) i = Current Density (µA/cm2)
EW = Equivalent Weight
= Corroded Metal Density (gram/cm3) 2.2.6 Scanning Electron Microscopy (SEM)
The surface of the corroded welding joint is tested by producing a specimen based on the size or capability of the SEM.
3. Result and Discussion 3.1. Welding Temperature
(a)
(b)
(c)
4
(d)
Figure 4. Temperature Distribution Graph (a) Specimen A, (b) Specimen B, (c) Specimen C, (d) Specimen D
The advancing side has a greater temperature than the receding side, as shown in Figure 4. This is due to the fact that the friction force between the tool and the base metal is complemented by the reverse of welding. The retreating side temperature is lower due to the direction of friction of the tool and base metal in the direction of welding [23][24]. The highest temperature occurs when the tool is in the
center position of the workpiece and the temperature decreases with increasing welding time and distance, this is due to the cooling process of the material as a result of conduction to the backing plate and room temperature [25]. The heat generated during welding is a mix of thermal conduction and heat by material plasticity [26] [27].
3.2. Visual Inspection
Table 2. shows that all specimens and welding positions produce flash (yellow arrows) that is quite rough on the top (1G) and bottom (4G) surfaces. At higher rotational speeds and lower welding speeds, the material undergoes severe plastic deformation, leading to excessive flash formation. This is due to the excessive heat that softens the test material and due to the tool pressing on the soft material so that it is lifted above the surface into flash [20][33].
Therefore, an optimal combination of welding speed and tool rotation speed must be maintained to prevent flash formation.
Table 2. Results of Visual Inspections
Specimen Flash Defects Welding Tool Position
1G 4G
Specimen A
Specimen B
Specimen C
Specimen D
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3.3. Radiography TestingBased on radiographic testing shown in Table 3., all specimens show Incomplete fusion (IF) defects caused by low heat input at the beginning of each welding and a rapid cooling process resulting in
insufficient plasticity of the material due to non- optimal welding speed and tool rotation speed [28].
To reduce defects in the connection, we must pay attention to dwell time, tool rotation speed, welding speed, tool geometry, and plate thickness [29].
Table 3. Results of DSFSW Radiography Testing
Specimen Defective Section (Incomplete Fusion)
Starting Point End Point
Specimen A
Specimen B
Specimen C
Specimen D
3.4. Microstructure
Figure 5. depicts the results of Weld Metal microstructure testing (WM). This section depicts the change in dimension and shape of the microstructure caused by solid plastic deformation, heat exposure, and product flows as during welding process as a result of tool stirring [30]. The heating that occurs even during weld metal causes recrystallization in the stir zone in the form of fine grains. Because DSFSW has no filler metal, there is no phase shift in the stir zone [31]. The phase formed in the stir zone is α-Al + Al-Si-Mg, the α (aluminum) phase is in the area with a light color, while the Al-Si-Mg (aluminum-silicon-magnesium) phase is in the area with a dark and grayish color in the form of sediment [32]. The α (aluminum) phase is shown with a red arrow line, while the remaining Al-Si-Mg (aluminum-silicon-magnesium) phase.
(a) (b)
56 mm
16 mm
91 mm 10 mm
100 mm 24 mm
79 mm 26 mm
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(c) (d)
Figure 5. Microstructure Weld Metal (a) Specimen A, (b) Specimen B, (c) Specimen C, (d) Specimen D
3.5. Corrosion Rate
The diagram below shows the comparison of corrosion rate calculation using NOVA software and Faraday's Law on DSFSW specimens.
(a)
(b)
(c)
Figure 6. Comparison Diagram of Corrosion Rate Values using NOVA Software vs Faraday's Law on DSFSW Specimens (a)Tool Position 1G, (b)Tool Position 4G,
(c)Base Metal
Table 4. Corrosion Rate Differences from NOVA Software and Faraday's Law
Specimen Tool Position 1G Tool Position 4G
Base Metal
A B C D A B C D
Difference
(mm/years) 0.00001 0.00012 0.00003 0.00002 0.00005 0.00005 0.00002 0.00002 0.00005
Figure 6. shows a comparison of the results of corrosion rate calculations using NOVA software and by using the Faraday's Law formula on DSFSW specimens at positions 1G, 4G and base metal. The following Table 4. is the difference in corrosion rate values between NOVA software and Faraday's Law.
The result difference is determined by the higher tool rotational speed, which creates greater heat during the welding process, resulting in severe deformation [33]. The high level of heat owing to frictional and semi cold work influences the corrosion rate, and the heat produces metallurgical transformations in the Heat Affected Zone (HAZ) and weld metal (WM) [34]. Due to increasing
tension, metallurgical unstable exposes the metal or material vulnerable to corrosion [14]. Stress and strain in weldment have already been found to have a significant effect on corrosion, which has a significant influence on the effectiveness of weld zone [20]. To increase a material's corrosion resistance, decrease the heat flow by raising the spindle speed [35].
3.6. SEM Testing
Depending on the SEM data, each specimen demonstrates that the corrosion type which occurs is pitting corrosion, which would be characterized by holes. The formation of holes in the corroded area indicates the level of surface degradation [36].
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Strong strain concentrations induced by heat welding cause pitting corrosion and the presence of fissures in the weld metal [37]. Corrosion resistance may decrease due to high heat input and low cooling ratewhich allows induction of segregation of alloying elements BM HAZ, and WM shows similar corrosion potential after welding process [38][39].
Table 5. HAZ Zone Result at 1000x Scale
Specimen Tool Position
1 G 4 G
Specimen A
Specimen B
Specimen C
Specimen D
Table 6. WM Zone SEM Results at 1000x Scale
Specimen Tool Position
1 G 4 G
Specimen A
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Specimen B
Specimen C
Specimen D
Table 7. BM Zone SEM Result at 1000x Scale
Base Metal
4. Conclusion
The purpose of this research is to identify the morphology of corrosion rate in AA6061 DSFSW joints which includes temperature, weld defects (visual inspection and radiography test), microstructure, corrosion rate and morphology of the corroded surface.
The temperature analysis results show that the Advancing Side (AS) has a higher temperature than the Retreating Side (RS), due to friction between the tool and specimen accompanied by differences in welding direction. Visual inspection shows that all specimens and welding positions produce flash that is quite rough on the top (1G) and bottom (4G) surfaces and radiographic test results show the presence of Incomplete Fusion (IF) in 4 specimens. Microstructure shows a change in shape and size, leading in crystallization as finer particles. There is a difference in
corrosion rate values after being investigated from NOVA Software and Faraday's Law. The result difference is impacted by high tool speed, which causes greater heat during in the weld metal and has an impact on SEM testing. The SEM test results show that the type of corrosion that occurs in DSFSW joints is pitting corrosion.
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