Analysis and Solutions of Common Defects in Laser Cladding

    As a core technology for surface strengthening and repair of high-end equipment, Laser Cladding achieves metallurgical bonding between alloy powder and the substrate surface through a high-energy laser beam, which can significantly improve the key properties of workpieces such as wear resistance and corrosion resistance. However, affected by multiple factors including the matching degree of process parameters, powder characteristics, substrate status, and environmental conditions, defects such as porosity, cracks, lack of fusion, and surface unevenness are prone to occur during the cladding process. These defects will seriously reduce the quality and service life of the cladding layer, and even lead to workpiece failure. Therefore, accurately identifying defect types, analyzing their causes, and adopting targeted solutions are crucial to ensuring the industrial application of laser cladding technology.

During the Laser Cladding process, porosity and cracks are the two most typical and harmful defects. Porosity mainly originates from moisture absorption and internal gas content of damp powder, or gas generated by the decomposition of oil stains and oxide scales on the substrate surface; if the molten pool exists for too short a time, the gas cannot escape in time, thus forming pores. Cracks are divided into hot cracks and cold cracks: hot cracks are mostly induced by the complex alloy composition of the cladding layer, the formation of low-melting eutectic phases during solidification, combined with thermal stress generated by rapid heating and cooling; cold cracks are mainly caused by excessive differences in thermal expansion coefficients between the substrate and the cladding layer, and the high brittleness of the hardened structure of the substrate. In addition, lack of fusion defects result from insufficient laser power, excessive scanning speed, or unstable powder feeding, which prevent effective metallurgical bonding between the powder and the substrate; surface unevenness is closely related to scanning speed, powder feeding rate, and uneven laser energy distribution.

   According to the causes of different defects, a full-process solution system of "source control + process optimization + post-processing" needs to be constructed. For porosity, the powder should be vacuum-dried at 120–150℃ for 2–4 hours to remove moisture before use; the substrate surface should be sandblasted and cleaned to remove impurities before Laser Cladding; at the same time, the laser power and scanning speed should be optimized to ensure sufficient existence time of the molten pool. To prevent and control cracks, it is necessary to select cladding powder matching the thermal expansion coefficient of the substrate, preheat the substrate at 200–400℃, adopt multi-layer and multi-pass cladding, and perform low-temperature tempering treatment afterward to release stress. For lack of fusion, it is necessary to accurately adjust the laser energy density to melt the substrate surface and ensure the stability of the powder feeding system; to solve the problem of surface unevenness, it can be achieved by reducing the scanning speed and matching the powder feeding rate with laser energy; for workpieces requiring high precision, subsequent machining processes can be added.

The prevention and control of Laser Cladding defects essentially lies in the precise matching of process parameters, material properties, and environmental conditions. With the development of laser processing technology, the application of intelligent means such as spot shaping and real-time monitoring provides a new path for the accurate identification and dynamic regulation of defects. In the future, in-depth research on the metallurgical reaction mechanism during the cladding process, combined with intelligent process optimization, will further reduce the defect rate, promote the wider application of laser cladding technology in high-end manufacturing, equipment repair and other fields, and provide reliable technical support for improving equipment performance and extending service life.