Optimization of rotary friction welding and mechanical locking method for enhanced joint strength in AA6063 aluminum alloys

Abstract

Context—Lightweight aluminum alloys are widely used in aerospace, automotive, and advanced manufacturing due to their high strength-to-weight ratio and corrosion resistance, making reliable joining technologies essential. rotary friction welding (RFW) is a solid-state technique capable of producing high-integrity joints with minimal distortion and fewer metallurgical defects than conventional fusion welding. It is particularly suitable for aluminum alloys, which are prone to thermal defects such as porosity, hot cracking, and microstructural degradation during conventional welding processes. However, frictional heat generated during RFW can still induce heterogeneous microstructural transformations and precipitation changes in heat-treatable alloys such as AA6063, potentially affecting joint performance. To address these limitations, alternative approaches that reduce heat dependency while improving joint stability have gained attention. The mechanical locking method (MLM) provides geometric interlocking at the joint interface and enhances mechanical stability with limited thermal influence. Nevertheless, the combined application of RFW and MLM and the interaction of their processing parameters remain insufficiently explored.

Objective—This study aims to optimize the hybrid RFW–MLM joining process for AA6063 aluminum alloy using response surface methodology (RSM). The research evaluates the effects of key parameters, including rotational speed, forging pressure, and MLM-related geometric features, on tensile strength and microstructural characteristics of the joints. In addition, a statistically validated predictive model is developed to determine the optimal processing window for maximum joint strength.

Method—Friction welding experiments were conducted using different combinations of rotational speed and forging pressure, while MLM geometric configurations were incorporated to enhance mechanical interlocking at the interface. Experimental design and parameter optimization were performed using RSM. The significance and adequacy of the developed quadratic model were evaluated through analysis of variance (ANOVA). Microstructural analyses were carried out to investigate phase transformations and precipitation behavior within the welded regions.

Results—Statistical evaluation confirmed the significance of the model with an F-value of 34.98, demonstrating strong predictive capability. Rotational speed and forging pressure were identified as the most influential parameters, contributing approximately 24% to the variation in joint strength. Residual analysis showed a normal distribution, confirming model reliability. Microstructural observations revealed the presence of S-phase, T-phase, Precipitate Free Zones (PFZ), and Guinier–Preston–Bagaryatsky (GPB) zones. Excessive frictional heating in the S12 sample group promoted T-phase formation, which may reduce joint strength.

Conclusion—The hybrid RFW–MLM technique significantly improves the mechanical performance of AA6063 aluminum alloy joints by combining metallurgical bonding with mechanical interlocking. The developed quadratic model demonstrated high predictive accuracy and identified rotational speed and forging pressure as the dominant parameters controlling joint strength. The optimized hybrid process provides a reliable and industrially applicable processing window for producing high-strength aluminum joints with improved microstructural stability.

Keywords

• Optimization
• mechanical;
• microstructural
• friction
• welding
• RSM

AA6063 alüminyum alaşımlarında eklem mukavemetini artırmak için döner sürtünme kaynağı ve mekanik kilitleme yönteminin optimizasyonu

Abstract

Arka Plan—AA6063 alüminyum alaşımı, yüksek özgül dayanımı, iyi korozyon direnci ve şekillendirilebilirliği nedeniyle havacılık, otomotiv ve ileri imalat uygulamalarında yaygın olarak kullanılmaktadır. Bu alaşımın güvenilir şekilde birleştirilmesinde döner sürtünme kaynağı (RFW), ergitme kaynak yöntemlerine göre daha düşük ısı girdisi, sınırlı deformasyon ve daha az metalurjik kusur sağlaması nedeniyle önemli avantajlar sunmaktadır. Ancak RFW sırasında oluşan sürtünme ısısı, çökelti dönüşümleri ve mikroyapısal heterojenlik oluşturarak birleşim performansını olumsuz etkileyebilmektedir. Bu nedenle, mekanik kilitleme yöntemi (MLM) ile RFW'nin birlikte kullanıldığı hibrit yaklaşımların geliştirilmesi, yüksek dayanımlı ve mikroyapısal açıdan kararlı birleşimlerin elde edilmesi açısından önem taşımaktadır.

Amaç—Bu çalışmada, AA6063 alüminyum alaşımının hibrit RFW–MLM yöntemiyle birleştirilmesinde dönme hızı, yığma basıncı ve MLM geometrik parametrelerinin çekme dayanımı ile mikroyapısal özellikler üzerindeki etkilerinin belirlenmesi, Tepki Yüzey Yöntemi (RSM) kullanılarak optimum işlem koşullarının ortaya konulması ve istatistiksel olarak doğrulanmış güvenilir bir tahmin modelinin geliştirilmesi amaçlanmıştır.

Yöntem—Hibrit RFW–MLM yöntemi kullanılarak farklı dönme hızı, yığma basıncı ve mekanik kilitleme geometrilerinde deneysel çalışmalar gerçekleştirilmiştir. Deney tasarımı ve parametre optimizasyonu Merkezi Kompozit Tasarım (CCD) tabanlı Tepki Yüzey Yöntemi ile yürütülmüş, geliştirilen ikinci dereceden regresyon modelinin yeterliliği ve parametrelerin istatistiksel anlamlılığı ANOVA ile değerlendirilmiştir. Birleşim bölgelerindeki faz oluşumları, çökelti davranışları ve mikroyapısal değişimler metalografik incelemelerle analiz edilmiştir.

Bulgular—Geliştirilen ikinci dereceden modelin istatistiksel olarak anlamlı olduğu (F=34,98) ve yüksek tahmin başarısı gösterdiği belirlenmiştir. Dönme hızı ile yığma basıncı, çekme dayanımını etkileyen en önemli işlem parametreleri olup toplam değişimin yaklaşık %24'ünü açıklamıştır. Artık analizleri model varsayımlarının sağlandığını ve modelin güvenilir olduğunu göstermiştir. Mikroyapı incelemelerinde S-fazı, T-fazı, Guinier–Preston–Bagaryatsky (GPB) bölgeleri ile Çökelti İçermeyen Bölgeler (PFZ) tespit edilmiş; özellikle S12 numune grubunda oluşan yüksek sürtünme ısısının T-fazı oluşumunu artırarak birleşim dayanımını olumsuz yönde etkileyebileceği belirlenmiştir.

Sonuç—Hibrit RFW–MLM yöntemi, metalurjik bağlanma ile mekanik kilitleme mekanizmasını bir araya getirerek AA6063 alaşımında yüksek mekanik performans ve gelişmiş mikroyapısal kararlılık sağlamıştır. Geliştirilen istatistiksel model, işlem parametrelerinin güvenilir biçimde optimize edilmesine olanak tanımış ve dönme hızı ile yığma basıncının birleşim dayanımını belirleyen temel parametreler olduğunu ortaya koymuştur. Elde edilen bulgular, hibrit RFW–MLM yönteminin yüksek dayanımlı alüminyum birleşimlerinin endüstriyel üretiminde uygulanabilir ve güvenilir bir alternatif olduğunu göstermektedir.

Keywords

• Optimizasyon
• mekanik
• mikro yapısal
• sürtünme; kaynak
• analiz
• RSM

References

1. Q. Nie, X. Wang, S. Wang, N. Li, X. Li, J. Li, Q. Yu, “Effect of post-weld heat treatment on the joint of friction-welded 1MnCrMoNi steel”, Science and Technology of Welding and Joining, 26(3), 220–226, 2021. https://doi.org/10.1080/13621718.2021.1882654.
2. M. Delgado, R. Flores, C. Santana, L. Reyes-Osorio, “Inspection of defects in friction stir welded Al-7075 T6 alloy”, Nondestructive Testing and Evaluation, 39(2), 276–292, 2024. https://doi.org/10.1080/10589759.2023.2194057.
3. V. Ajay, M. N. Kumar, N. K. Babu, T. M. Kumar, K. V. Krishna, G. M. Reddy, “Rotary friction welding of Inconel 718-AISI 304 stainless steel dissimilar joint”, Materials Science and Technology, 39(15), 1950–1960, 2023. https://doi.org/10.1080/02670836.2023.2187146.
4. B. A. Humphreys, “Thompson Friction Welding: A Practical Guide to Friction Welding”, Hereward Rise, Halesowen, WEST Midlands, B62 8AN, 26 September 2004, https://www.academia.edu/8721538/Thompson_Friction_Welding_A_Practical_Guide_to_Friction_Welding_A_Practical_Guide_to_Friction_Welding (13.11.2023).
5. B. S. Taysom, T. W. Nelson, C. D. Sorensen, R. DiDomizio, S. Huang, I. R. Potts, “Weld strength and heat-affected zone size in friction welded NFA and CostE”, Science and Technology of Welding and Joining, 26(8), 581–589, 2021. https://doi.org/10.1080/13621718.2021.1979725.
6. D. K. Rajak, D. D. Pagar, P. L. Menezes, A. Eyvazian, “Friction-based welding processes: friction welding and friction stir welding”, Journal of Adhesion Science and Technology, 1–25, 2020. https://doi.org/10.1080/01694243.2020.1780716.
7. P. Li, S. Wang, Y. Q. Xia, X. H. Hao, Z. K. Lei, H. G. Dong, “Inhomogeneous microstructure and mechanical properties of rotary friction welded AA2024 joints”, Journal of Materials Research and Technology - JMR&T, 9(3), 5749–5760, 2020. https://doi.org/10.1016/j.jmrt.2020.03.100.
8. A. J. Guevara-Muñoz, D. A. Hincapie-Zuluaga, M. A. Rodríguez-Cabal, J. A. Sierra-Del-Rio, R. F. Colmenares-Quintero, E. Torres-Lopez, “2D Numerical Analysis of an H-Darrieus Hydrokinetic Turbine with Passive Improvement Mechanisms”, Engineering Transactions, 71(4), 553–569, 2023. https://doi.org/10.24423/EngTrans.3111.20231107.

9. E. Görgün, “Characterization of superalloys by artificial neural network method”, International Symposium on Applied Mathematics and Engineering (ISAME22), İstanbul, Türkiye, 21-23 January 2022, http://www.ntmsci.com/Areas/Conferences/FilesAndImages/19/ISAME-1.pdf#page=66 (02. 06. 2026).
10. G. Emre, A. Akkus, M. B. Karamış, “Wear resistance of polymethyl methacrylate (PMMA) with the addition of bone ash, hydroxylapatite and keratin”, IOP Conference Series: Materials Science and Engineering, 295, 012004, 2018. https://doi.org/10.1088/1757-899X/295/1/012004.
11. E. Gorgun, “Ultrasonic testing and surface conditioning techniques for enhanced thermoplastic adhesive bonds”, Journal of Mechanical Science and Technology, 38(3), 1227–1236, 2024. https://doi.org/10.1007/s12206-024-0218-6.
12. H. Şenol, M. Erşan, E. Görgün, “Optimization of temperature and pretreatments for methane yield of hazelnut shells using the response surface methodology”, Fuel, 271, 117585, 2020. https://doi.org/10.1016/j.fuel.2020.117585.
13. M. H. R. Sobuz, M. K. I. Kabbo, T. S. Alahmari, J. Ashraf, E. Gorgun, M. M. H. Khan, “Microstructural behavior and explainable machine learning aided mechanical strength prediction and optimization of recycled glass-based solid waste concrete”, Case Studies in Construction Materials, 22, e04305, 2025. https://doi.org/10.1016/j.cscm.2025.e04305.
14. H. Senol, I. T. Cakir, F. Bianco, E. Gorgun, “Improved methane production from ultrasonically-pretreated secondary sedimentation tank sludge and new model proposal: Time series (ARIMA)”, Bioresource Technology, 391, 129866, 2024. https://doi.org/10.1016/j.biortech.2023.129866.
15. A. Canan, R. Calhan, M. Ozkaymak, “Investigation of the effects of blast furnace slag ratio, total solid, and pH on anaerobic digestion: modeling and optimization by using response surface methodology”, Biomass Conversion and Biorefinery, 11(5), 2219–2232, 2021. https://doi.org/10.1007/s13399-021-01865-4.
16. E. Görgün, “Çoklu Yükleme Koşulları Altında Yük Vagonu Şasisinin Topoloji Optimizasyonu”, Karadeniz Fen Bilimleri Dergisi, 12(2), 593–604, 2022. https://doi.org/10.31466/kfbd.1078425.
17. E. Görgün, M. Erşan, “Enhanced Corrosion Resistance of X120Mn12 Steel in Acidic Media by a Novel Nanolignin-Based Protective Coating”, Black Sea Journal of Engineering and Science, 8(4), 1067–1075, 2025. https://doi.org/10.34248/bsengineering.1673480.
18. E. Görgün, “Ultrasonik Muayene Prob Çaplarının Darbe Yankı Değerine Etkisinin Araştırılması”, Karadeniz Fen Bilimleri Dergisi, 12(1), 381–389, 2022. https://doi.org/10.31466/kfbd.1077386.
19. E. Görgün, “Pleksiglas Takozların Farklı Frekans ve Çaptaki Ultrasonik Probların Muayene Hassasiyetine Etkisi”, Afyon Kocatepe Üniversitesi Fen ve Mühendislik Bilimleri Dergisi, 22(2), 431–435, 2022. https://doi.org/10.35414/akufemubid.1036049.
20. D. Anaklı, E. Görgün, M. Erşan, A. Elmavle, “Bakır destekli bor–grafen nanoplaka hibrit nanokompozitlerinde grafen oksit yüklemesinin elektriksel iletkenlik üzerine etkilerinin Box–Behnken tasarımı ile optimizasyonu”, Niğde Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 15, 1796452, 2026. https://doi.org/10.28948/ngumuh.1796452.
21. T. X. Tang, Q. Y. Shi, B. W. Lei, J. Zhou, Y. X. Gao, Y. Q. Li, G. Zhang, G. Q. Chen, “Transition of interfacial friction regime and its influence on thermal responses in rotary friction welding of SUS304 stainless steel: A fully coupled transient thermomechanical analysis”, Journal of Manufacturing Processes, 82, 403–414, 2022. https://doi.org/10.1016/j.jmapro.2022.08.016.
22. E. Bulut, E. Görgün, “A New Approach to Non-Destructive Testing Using OpenCV-Based Image Processing”, Black Sea Journal of Engineering and Science, 8(4), 1152–1159, 2025. https://doi.org/10.34248/bsengineering.1685735.
23. R. R. Kumar, J. M. Babu, B. Saleh, H. Fayaz, A. Chandrashekar, T. Gera, K. S. Nisar, C. A. Saleel, “Experimental and analytical investigation on friction welding dissimilar joints for aerospace applications”, Ain Shams Engineering Journal, 14(2), 101853, 2023. https://doi.org/10.1016/j.asej.2022.101853.
24. S. X. Zhao, M. J. Wang, S. Z. Kou, Z. Jia, W. J. Wang, Q. Li, G. N. Luo, “Realization of ODS-Cu/T91 Tube-to-tube Joining with Rotary Friction Welding”, Fusion Engineering and Design, 158, 111699, 2020. https://doi.org/10.1016/j.fusengdes.2020.111699.
25. P. Y. Chang, Y. J. Chan, S. K. Arumugasamy, Y. K. Wan, J. W. Lim, “Optimisation of anaerobic digestion of palm oil mill effluent with biochar addition: Synergistic application of Artificial neural network and response Surface Methodology”, Fuel, 398, 135514, 2025. https://doi.org/10.1016/j.fuel.2025.135514.
26. R. V. Marode, M. Awang, V. S. R. Janga, “Computational Modelling and Comparative Analysis of Friction Stir Welding and Stationary Shoulder Friction Stir Welding on AA6061”, Crystals, 13(9), 1317, 2023. https://doi.org/10.3390/cryst13091317.
27. N. K. Mishra, A. Shrivastava, “Improvement in strength and ductility of rotary friction welded Inconel 600 and stainless steel 316L with Cu interlayer”, CIRP Journal of Manufacturing Science and Technology, 41, 19–29, 2023. https://doi.org/10.1016/j.cirpj.2022.12.006.
28. F. Jin, J. M. Shi, G. D. Wen, B. L. Fu, J. J. Shen, S. Q. Wang, Y. B. Wu, J. T. Xiong, J. L. Li, “Frictional heat induced morphological responses at the interface in rotary friction welding of austenitic alloys: corona-bond and heat-pattern”, Journal of Materials Research and Technology–JMR&T, 23, 5972–5992, 2023. https://doi.org/10.1016/j.jmrt.2023.02.221.
29. F. Jin, H. D. Rao, Q. Wang, G. D. Wen, P. Liu, J. T. Liu, J. J. Shen, J. L. Li, J. T. Xiong, N. S. Ma, “Heat-pattern induced non-uniform radial microstructure and properties of Ti-6Al-4V joint prepared by rotary friction welding”, Materials Characterization, 195, 112536, 2023. https://doi.org/10.1016/j.matchar.2022.112536.
30. A. Ghiasvand, M. M. Yavari, J. Tomków, J. W. G. Guerrero, H. Kheradmandan, A. Dorofeev, S. Memon, H. A. Derazkola, “Investigation of Mechanical and Microstructural Properties of Welded Specimens of AA6061-T6 Alloy with Friction Stir Welding and Parallel-Friction Stir Welding Methods”, Materials, 14(20), 6003, 2021. https://doi.org/10.3390/ma14206003.
31. Y. Belkahla, A. Mazouzi, S. E. Lebouachera, A. J. Hassan, M. Fides, P. Hvizdos, B. Cheniti, D. Miroud, “Rotary friction welded C45 to 16NiCr6 steel rods: statistical optimization coupled to mechanical and microstructure approaches”, International Journal of Advanced Manufacturing Technology, 116(7-8), 2285–2298, 2021. https://doi.org/10.1007/s00170-021-07597-z.
32. Y. Y. Wang, K. Sebeck, M. Tess, E. Gingrich, Z. L. Feng, J.A. Haynes, M.J. Lance, G. Muralidharan, R. Marchel, T. Kirste, D. Pierce, “Interfacial microstructure and mechanical properties of rotary inertia friction welded dissimilar 422 martensitic stainless steel to 4140 low alloy steel joints”, Materials Science and Engineering A – Structural Materials Properties Microstructure and Processing, 885, 145607, 2023. https://doi.org/10.1016/j.msea.2023.145607.
33. S. Kumar, P. S. Grant, K. A. Q. O’Reilly, “Evolution of Fe Bearing Intermetallics During DC Casting and Homogenization of an Al-Mg-Si Al Alloy”, Metallurgical and Materials Transactions A – Physical Metallurgy and Materials Science, 47A(6), 3000–3014, 2016. https://doi.org/10.1007/s11661-016-3451-5.
34. H. B. Geng, G. F. Xu, J. C. Liu, H. Lou, “Rotary friction welding of pure aluminum to preheated brass”, Welding in the World, 66(11), 2371–2376, 2022. https://doi.org/10.1007/s40194-022-01367-5.
35. J. Zhao, Z. Q. Liu, B. Wang, “Surface texture and friction property of Ti-6Al-4V processed by rotary ultrasonic rolling”, International Journal of Advanced Manufacturing Technology, 115(1-2), 463–474, 2021. https://doi.org/10.1007/s00170-021-07197-x.
36. R. Selvaraj, K. Shanmugam, P. Selvaraj, B. P. Nagasai, V. Balasubramanian, “Optimization of process parameters of rotary friction welding of low alloy steel tubes using response surface methodology”, Forces in Mechanics, 10, 100175, 2023. https://doi.org/10.1016/j.finmec.2023.100175.