Effects of mechanical vibration on the physical, metallurgical and mechanical properties of cast A308 (LM21) aluminum alloy

This study investigated the microstructure, physical, and mechanical properties of die-cast A308 alloy subjected to mechanical vibration during solidification. Different frequencies (0, 20, 30, 40, and 50 Hz) at constant amplitude (31 μm) were employed using a power amplifier as the power input device. X-ray diffraction, optical microscopy, and scanning electron microscopy were used to examine the morphological changes in the cast samples under stationary and vibratory conditions. Metallurgical features of the castings were evaluated using ImageJ software. The average values of metallurgical features, including primary α-Al grain size, dendrite arm spacing, average area of eutectic silicon, aspect ratio, and percentage porosity, reduced by 34%, 59%, 56%, 22%, and 62%, respectively, at 30 Hz frequency compared with stationary casting. Mechanical tests of the cast samples showed that the yield strength (YS), ultimate tensile strength (UTS), percentage elongation (%EL), and microhardness (HV) increased by 8%, 13%, 17%, and 16%, respectively, at 30 Hz frequency compared with stationary casting. The fractured surface of the tensile specimens exhibited mixed-mode fracture behavior because of brittle facets, cleavage facets, ductile tearing, and dimple morphologies. The presence of small dimples showed that plastic deformation occurred before fracture.