Dynamics of the Molten Layer at the Armature-Rail Interface Under Extreme Electromagnetic-Thermal-Mechanical Loads

In electromagnetic launch technology, multi-physics coupling at the armature/rail (A/R) interface leads to molten metal formation, which degrades interfacial contact, friction, and system performance. To clarify the evolution mechanism of this molten layer, the present work investigates armature surface erosion and rail aluminum deposition under different current levels and multiple launch cycles. A small-scale electromagnetic launch platform was used together with high-speed imaging and scanning electron microscopy for characterization. The results reveal a dual-mode erosion characteristic: under low-current conditions, Joule heating dominates, forming discrete molten pits; under high-current conditions, coupling between electromagnetic and inertial forces drives the molten metal to flow and spread, forming a continuous smoothed surface. As the number of launches increases, the aluminum deposition layer thickens, reducing interfacial thermal conductivity and causing a transition from molten metal conduction to a hybrid arc-molten metal conduction mode. The deposition layer exhibits a gradient distribution, with its non-uniformity arising from the competing effects of cooling rate variations along the sliding direction and the Lorentz force. This study clarifies the evolution mechanism of molten metal at the A/R interface under multi-physics coupling, providing experimental evidence for optimizing interface design and enhancing system performance.