This paper deals with the selection of the optimal material for railway wagons, from among three different steel and three aluminium based materials, by using four different Multicriteria Decision Making Methods (MCDM) and comparing their ranking of the materials. We analysed: Dual-Phase 600 steel, Transformation-Induced Plasticity (TRIP) 700 steel, Twinning-Induced Plasticity (TWIP) steel, Aluminium (Al) alloys, Al 6005-T6, and Al 6082-T6, and porous Al structure with closed cells. Four different MCDM methods were used: VIKOR, TOPSIS, PROMETTHEE and the Weighted aggregated sum product assessment method (WASPAS). Key material properties that were used in the MCDM analysis were: density, yield strength (Y.S.), tensile strength (T.S.), Y.S./T.S. ratio, Youngs modulus (Y.M.), cost and corrosion resistance (C.R.). Research results indicate that aluminium and its alloys prove to be the most suitable material, based on setup criteria. Advanced steels also achieved good ranking, making them a valid option, immediately behind lightweight aluminium alloys. Porous aluminium did not perform well, according to the used MDCM methods, mainly due to the significantly lower strength exhibited by the porous structures in general.

This paper presents the development and industrial implementation of Friction Stir Welding (FSW) for aluminium roof panel assemblies of metro vehicles within the Stadler SBB project. The base material is EN AW 6005A T6 extruded aluminium alloy (group 23.1, EN 15608), with a wall thickness of 3.5 mm and panel dimensions of 2,214 × 2,348 mm. FSW (ISO 4063, process No. 43) was selected for its advantages over fusion welding: reduced heat input, no filler material or shielding gas, minimal distortion, and superior surface finish. Welding was performed on a CNC milling machine at 170 cm/min using a tool with a 15 mm concave shoulder and 6 mm threaded probe. Process qualification per ISO 25239-4 included tensile, bend, and macrographic testing, with all results meeting quality level C (ISO 25239-5). The symmetrical welding sequence covered 12 joints per assembly (27.7 m total), with a maximum pre-weld gap of 0.3 mm, under a three-phase quality control plan. The results confirm FSW as a reliable, efficient, and environmentally sound solution for serial production of aluminium railway components.