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

The present investigation deals with the improvement in microstructure, physical, and mechanical properties of die-cast A308 alloy subjected to mechanical vibration during solidification. The 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 diffractometer, 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 castings were evaluated by ImageJ analysis software. The average values of metallurgical features, i.e., primary α-Al grain size, dendrite arm spacing (DAS), avg. area of eutectic silicon, aspect ratio, and percentage porosity were reduced by 34, 59, 56, 22, and 62% respectively at 30 Hz frequency compared to stationary casting. The mechanical tests of cast samples showed that yield strength, ultimate tensile strength, elongation, and microhardness were increased by 8, 13, 17, and 16%, respectively, at 30 Hz frequency compared to stationary casting. The fractured surface of tensile specimens exhibited mixed-mode fracture behavior due to the appearance of brittle facets, cleavage facets, ductile tearing, and dimple morphologies. The presence of small dimples showed some plastic deformation occurred before fracture.