The effects of laser energy density on the re-manufacturing of LZ50 axle via extreme high-speed laser cladding: microstructure, mechanical property, and fatigue performance

In the bogie structure, wheels, axles, and brake discs are critical components and are prone to foreign object impact, abrasive wear and corrosion. Re-manufacturing of rail transit components not only reduces the operating costs of railway network, but also saves metallic resource and cuts the carbon footprint. In this work, scaled samples were cut from scrapped axle, and Fe-based alloy powder was deposited on the surface of axle substrate via extreme high-speed laser cladding (EHLA) method. The effects of laser energy density on the microstructure evolution, mechanical properties, crack propagation resistance, and rotational bend fatigue performance of repaired samples were thoroughly investigated. In addition, an innovative deposition strategy with a gradually-increased laser energy density was proposed to minimize the thermal impact without compromising deposition efficiency. With this method, the tensile elongation, shear plasticity, and crack propagation resistance were enhanced as a result of reduced residual stress level and less thermal impact to substrate. Meanwhile, the rotational bend fatigue experiments indicated that the Fe-based cladding layer exhibited a superior fatigue strength to LZ50 substrate. However, the ductility of re-manufactured samples was still inferior to substrate due to the coated structure, making it could not deform coordinately with substrate under the external loading.