Effect of Tool Pin Diameter on the Tensile Strength of Friction Stir Welded AA6061 Joints: Implications for Railway Carbodies

Henry Widya Prasetya (Politeknik Perkeretaapian Indonesia Madiun)
Dadang Sanjaya Atmaja (Politeknik Perkeretaapian Indonesia Madiun)
I Made Agus Putrawan (Politeknik Negeri Bali)
Dimas Adi Perwira (Politeknik Perkeretaapian Indonesia Madiun)
Ilham Satrio Utomo (Politeknik Perkeretaapian Indonesia Madiun)
Moch Aziz Kurniawan (Politeknik Keselamatan Transportasi Jalan)

Journal of Railway Transportation and Technology
Vol. 5 No. 2 (2026): November

Friction stir welding (FSW) is a solid-state joining process that is increasingly used to fabricate aluminum railway carbodies. This study examined the effect of tool pin diameter on the tensile properties of FSW joints in 6 mm thick AA6061-T6 aluminum plates. High-speed steel tools with a 13 mm flat shoulder and straight cylindrical pins of 3, 4, and 5 mm diameter were fabricated by turning, and butt joints were welded on a conventional milling machine at a rotational speed of 1130 rpm, a traverse speed of 20 mm/min, and a tilt angle of 3°. Three joints were produced for each pin diameter (n = 3), and one transverse tensile specimen was tested from each joint. Results are reported as mean ± standard deviation and were analyzed using one-way ANOVA, the Kruskal–Wallis test, and Spearman’s rank correlation. The mean tensile strength decreased from 210.06 ± 5.87 MPa with the 3 mm pin to 190.96 ± 26.57 MPa and 146.36 ± 62.26 MPa with the 4 and 5 mm pins, respectively, while the scatter increased with pin diameter. Owing to the small sample size and large scatter, the differences among group means were not statistically significant (p = 0.206); however, pin diameter was negatively correlated with tensile strength (ρ = −0.74, p = 0.023). Visual inspection revealed less weld flash with the 3 mm pin, consistent with the smaller volume of material displaced by the pin. Within the tested range, the 3 mm pin provided the highest and most consistent tensile strength.