Friction stir welding (FSW) is one of the primary fabrication techniques for joining different components, and it has become popular, especially in aluminum alloy structures for marine applications. The welded joint with the friction stir process greatly depends on the process parameters, i.e., feed rate, rotational speed, and pin profile of the tool. In the current study, plates of aluminum 5451 alloy were joined by the FSW technique, and the Taguchi method was used to find the process parameters at an optimal level. The maximum value of tensile strength, i.e., 160.6907 MPa, was achieved using optimum welding conditions of a tool rotation speed of 1400, a feed rate of 18 mm/min, and the tool pin with threads. The maximum value of hardness, i.e., 81.056 HV, was achieved using optimum conditions of 1200 tool rotational speed and a feed rate of 18 mm/min with a tool pin profile having threads. In addition, the contribution in terms of the percentage of each input parameter was found by the analysis of variance (ANOVA). The ANOVA results revealed that the pin profile of the tool has the maximum contribution of 67.77% and 62.42% in achieving the optimum value of tensile strength and hardness, respectively. The study also investigated the joint efficiency of the friction stir welded joint, hardness at the weld zone, and metallography on FSW samples at the optimized level. The effectiveness and reliability of FSW joints for shipping industry applications can be observed by joint efficiency. That was investigated at optimum conditions, and it comes out to be 80.5%.

This study investigates the coefficient of friction (COF) and wear behavior in fretting regimes—stick, stick–slip, and gross sliding—under dry and oil-lubricated conditions. Fretting tests were conducted by increasing oscillation amplitude from a few micrometers to 48 µm. In dry conditions, displacement amplitude initially rose rapidly, stabilizing after about 5 million load cycles, indicating steady-state behavior. The friction ratio (FR) surged early, peaking between 0.7 and 1.0, before declining to stable values, suggesting a shift from adhesive to stable frictional interaction. The minimal slip amplitude confirmed the predominance of the stick regime. Conversely, in oil-lubricated conditions, displacement amplitude stabilized after an initial increase, achieving higher amplitudes than in dry tests. The FR started below 0.2, gradually increasing to a peak around 10,000 load cycles for higher oscillation amplitudes (e.g., 15 µm), reflecting the lubricant’s role in reducing metal-to-metal contact. COF curves in lubricated tests showed smoother transitions and lower peak values compared to dry tests. These findings highlight the lubricant’s effectiveness in minimizing adhesion and enhancing sliding efficiency, offering insights for optimizing material performance in engineering applications.