The Enhancement of Microstructures and Mechanical Characteristics for Sand Casting A357 Alloys with Magnetic Fields by Helmholtz Coils

The influence of external magnetic field in the sand casting process on the microstructures and mechanical properties of A357 aluminum-silicon (Al–Si) alloys was investigated. Different magnetic field intensities such as 0, 6.3, and 10.7 mT were applied respectively by Helmholtz coils with an autotransformer. Applied an external magnetic fields during the solidification process, the microstructures of as-cast A357 alloy performed grain refinement of α -Al, reduction of secondary dendritic arm spacing, and fibrous structure of eutectic silicon. After T6 heat treatment, the morphology of eutectic silicon particles became fragmented and spheroidized. Therefore, the magnetic field enhanced the mechanical properties of A357 alloys, including hardness, ultimate tensile strength (UTS), yield strength (YS), and elongation (El). Compared the samples without magnetic field and with the field of 10.7 mT, the values of hardness, UTS, YS and El increased 17.9%, 10.6%, 8.8%, and 48%, respectively. The higher the magnetic field we apply, the better performance of sand-cast A357 we can get. Moreover, the magnetic field during A357 solidification process attributed to the preferred orientation (111) of α -Al and uniformly dimples in fractography. In conclusion, an inexpensive and facile technique has been proposed to enhance the quality index of the sand-casting A357 alloys via the influence by external magnetic fields on the microscopic properties of materials, especially for α -Al grain refinement and eutectic-silicon spheroidization.