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<p>The present study investigates the underwater friction stir welding (UFSW) of dissimilar aluminum alloys AA6063-T6 and AA5083-H32, widely used in marine, transportation, and structural applications. The novelty lies in the systematic evaluation of key process parameters, namely tilt angle, rotational speed, and welding speed, under controlled underwater cooling conditions, which remains limited for this alloy combination. Experiments were conducted using a specially developed setup on a conventional milling machine integrated with a water tank. A Taguchi L16 orthogonal array was employed to optimize process parameters. Mechanical properties such as ultimate tensile strength (UTS), yield strength, elongation, impact toughness, and microhardness were evaluated along with detailed microstructural characterization using optical microscopy, SEM-EDS, XRD, and fractography. The results revealed that optimized welding conditions produced defect-free joints with stable material flow and uniform grain refinement in the stir zone, achieving a maximum UTS of 265&#xa0;MPa compared to a minimum of 245&#xa0;MPa, corresponding to an improvement of approximately 20&#xa0;MPa (about 8.16%). Although the percentage increase is moderate, it is significant in solid-state welding due to its strong association with defect elimination and improved ductility. Suboptimal conditions resulted in defects such as voids, cracks, and tunnel formations, reducing mechanical performance. Microstructural analysis confirmed refined grains and onion-ring structures under optimized conditions. SEM-EDS identified Al-Mg and Al-Zn-Mg intermetallics, while XRD detected the aluminum matrix and Al2Cu phases. Fractography indicated ductile fracture in optimized welds and mixed fracture in defective joints. The study highlights the importance of parameter optimization for enhancing weld integrity and performance.</p>

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Microstructural Analysis of Underwater Friction Stir Welding of Dissimilar Aluminum Alloys AA6063-T6 and AA5083-H32

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Sachin Gadakh,
  • Chitresh Nayak,
  • Birajashis Pattnaik,
  • Kiran Wakchaure

摘要

The present study investigates the underwater friction stir welding (UFSW) of dissimilar aluminum alloys AA6063-T6 and AA5083-H32, widely used in marine, transportation, and structural applications. The novelty lies in the systematic evaluation of key process parameters, namely tilt angle, rotational speed, and welding speed, under controlled underwater cooling conditions, which remains limited for this alloy combination. Experiments were conducted using a specially developed setup on a conventional milling machine integrated with a water tank. A Taguchi L16 orthogonal array was employed to optimize process parameters. Mechanical properties such as ultimate tensile strength (UTS), yield strength, elongation, impact toughness, and microhardness were evaluated along with detailed microstructural characterization using optical microscopy, SEM-EDS, XRD, and fractography. The results revealed that optimized welding conditions produced defect-free joints with stable material flow and uniform grain refinement in the stir zone, achieving a maximum UTS of 265 MPa compared to a minimum of 245 MPa, corresponding to an improvement of approximately 20 MPa (about 8.16%). Although the percentage increase is moderate, it is significant in solid-state welding due to its strong association with defect elimination and improved ductility. Suboptimal conditions resulted in defects such as voids, cracks, and tunnel formations, reducing mechanical performance. Microstructural analysis confirmed refined grains and onion-ring structures under optimized conditions. SEM-EDS identified Al-Mg and Al-Zn-Mg intermetallics, while XRD detected the aluminum matrix and Al2Cu phases. Fractography indicated ductile fracture in optimized welds and mixed fracture in defective joints. The study highlights the importance of parameter optimization for enhancing weld integrity and performance.