Effects of vibration frequency on microstructure, mechanical properties, and fracture behavior of A356 aluminum alloy obtained by expendable pattern shell casting

A simple, economic, and effective mechanical vibration method was introduced into the solidification process of A356 aluminum alloy during the expendable pattern shell casting process, and the effects of vibration frequency on microstructure, mechanical properties, and fracture behavior of the A356 alloy were investigated. Obtained results showed that the sizes and morphologies of alpha-Al primary phase and eutectic silicon particles were significantly improved by the mechanical vibration, and the mechanical properties and density of the A356 alloy greatly increased. With increasing vibration frequency, the grain size and secondary dendrite arm spacing (SDAS) continuously decreased, and the shape factor increased, and the mechanical properties and density of the A356 alloy gradually increased. With a vibration frequency of 100 Hz, the grain size and SDAS decreased by 32 and 19 %, respectively, and the shape factor increased by 262 %, and the average length, width, and aspect ratio of the silicon particles decreased by 45, 6, and 42 %, respectively, compared to that of the sample without vibration. Meanwhile, the tensile strength, yield strength, elongation, and hardness of the A356 alloy sample were, respectively, 35, 42, 57, and 28 % higher than those of the sample without vibration. In addition, the mechanical vibration changed the fractograph of the A356 alloy from a clear brittle fracture nature of the alloy without vibration to an obvious dimple fracture nature, and with the increase of vibration frequency, the dimples were very deep and well distributed with a high density.