Combined effects of mechanical vibration and wall thickness on microstructure and mechanical properties of A356 aluminum alloy produced by expendable pattern shell casting

In the present work, the combined effects of mechanical vibration and wall thickness on the microstructure and mechanical properties of A356 aluminum alloy produced by the expendable pattern shell casting process were investigated. It has been found that with the increase of wall thickness, the morphologies of the α-Al primary phase and eutectic silicon phase of the samples obtained from the conventionally cast evolved from a fine dendrite to a coarse dendrite and from a fibrous structure to a plate-like structure, respectively, and the mechanical properties of A356 aluminum alloy decreased continuously. After the mechanical vibration was applied, the coarser dendrites transformed into the fine equiaxed grains, and the size, morphology and distribution of the α-Al primary phase and eutectic silicon particles as well as SDAS were improved significantly. Meanwhile, the mechanical properties and density of A356 aluminum alloy increased greatly, and the tensile strength, yield strength, elongation as well as hardness of the sample with 40mm wall thickness were 35%, 42%, 63% and 29% higher than that of the conventionally cast under the T6 condition, respectively. The effect degree of the mechanical vibration on the microstructure and mechanical properties increased with increasing wall thickness. Furthermore, the mechanical vibration changed the fracture mode of A356 aluminum alloy from a transgranular fracture mode of the conventionally cast to an intergranular fracture mode.