The Effect of Vacuum on the Mechanical Properties of Sand Cast AA6061 Alloy

The application of vacuum in casting technology is very limited. In the present scenario, the vacuum is mainly used in die casting or investment casting, but the application of vacuum in sand casting is not known yet. In the present investigation, the author did a sand casting process under a vacuum, where the melting and pouring of metals were carried out in a vacuum atmosphere. AA6061 castings were made by sand casting under vacuum (SCUV) process in two different absolute pressure of 110 mbar and 56 mbar, and conventional sand casting process at atmospheric pressure. The effect of vacuum on the porosity and mechanical properties of the castings were investigated and compared with the conventional sand casting process. The results revealed that SCUV process reduces the porosity and improves the mechanical properties of sand cast AA6061 alloy. The pore size and the amount of porosity were significantly reduced from 1.548% at atmospheric pressure to 0.302% at 56 mbar of absolute pressure, i.e., 80.49% of reduction. The result also revealed that the mechanical properties of sand casting under vacuum were significantly improved, especially with the ultimate tensile strength from 276.2 to 309.8 MPa, i.e., 12.17% improvement, and elongation increased from 9.8 to 13.15%, i.e., 34.18% improvement. The gases present inside the mold cavity become the final gas porosity in SCUV. In addition, scanning electron microscopy analysis shows solidification shrinkages present in sand cast. SCUV reduces the size of porosity defect that can improve the stress distribution and slow down the crack propagation in sand castings. Therefore, the SCUV enhanced the ultimate tensile strength and elongation of sand casting.