Increase of a Fatigue Life of a Silumin by Electron-Beam Processing

Abstract

At present, the aluminium-alloy productions become increasingly popular in different branches of industry. However, the relatively low strength properties of silumin significantly restrict its scope of application. Silumins are not strengthened by heat treatment due to the small differences in the solubility of silicon at the high and low temperatures. Therefore, modification is the most important method of improving their mechanical properties. Processing of eutectic silumin by high-intensive electron beam in various regimes is carried out. High-cycle fatigue tests are performed to determine irradiation regime allowing increasing the material fatigue life by more than 3.5 times. Investigations of structure–phase states and defect substructure of silumin subjected to high-cycle fatigue tests up to failure are carried out by methods of the scanning and transmission electron-diffraction microscopy. As shown for the regime of partial melting of the irradiation surface, the process of surface modification is accompanied with the formation of numerous large micropores over the boundary plate–matrix and microcracks located in the silicon plates. A multimodal structure (grains of 30–50 μm sizes and silicon particles of up to 10 μm located on the boundaries) is formed in stable melting regime as well as subgrain structure in the form of crystallization cells of sizes from 100 nm up to 250 nm). As revealed, the sources of fatigue microcracks are silicon plates of the micron and submicron sizes, which are not soluble at the electron-beam treatment. The possible reasons of the silumin fatigue life increasing under electron-beam treatment are discussed. As shown, the main reasons for silumin fatigue-life increase are the considerable increase of the critical crack length, the safety coefficient, and the reduction of average distance between fatigue striations (crack path for loading cycle), the formation of multimodal, multiphase, submicro- and nanosize structure. The tribology and strength properties of silumin surface after electron-beam treatment and fatigue tests are studied; and hardness decrease, wear rate, and friction coefficient increase with the growth of cycles’ number are revealed. The possible reasons for deterioration of the tribology and strength properties of silumin surface layers are discussed.

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