A distinctive weld strategy enables dissimilar material hairpin joining for next generation high frequency motors

The design of efficient, lightweight stator hairpins, i.e., featuring both Aluminium and Copper (Al-Cu) windings, is at the core of the future of electric vehicle powertrains. However, reliable dissimilar Al-Cu hairpin joints remain a challenge due to their differing thermal properties and the formation of brittle intermetallic compounds (IMCs) during welding. In this paper, a predetermined sample placement, laser beam modulation, and trajectory optimisation are proposed to control heat flow and interfacial reactions during Al-Cu welding. Using a spiral laser beam path with a multi-pass thermal cycle yields stable joints free of defects, with significantly improved mechanical and electrical properties. The optimised beam modulation reduces localised overheating leading to homogeneous melt-pool dynamics, and suppresses excessive IMC growth, favouring a fine-grained interfacial microstructure. Quantitative analyses show a 32% decrease in IMC fraction, up to 70% decrease in porosity and 75% increase in tensile strength when compared to traditional welding (beam path). These results clarify the key role of spatial-temporal energy control in the design of microstructural evolution at dissimilar metal interfaces and show a feasible path for the design of high-performance and low-resistance Al-Cu connections for the next-generation of high-frequency electric motor systems. • Spiral beam path in dissimilar welds achieves deep penetration and low porosity. • Three-step welding process minimises Kirkendall void formation. • Al and Cu sample height shift enables the elimination of interfacial cracking. • Optimised Al-Cu welds show greater tensile strength and decreased hardness. • Electrical resistance test confirms the viability of optimised Al-Cu hairpins.