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

Öz

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.

Anahtar Kelimeler

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

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

Öz

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.

Anahtar Kelimeler

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

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