The Effect of Vacuum on the Mechanical Properties of Die Cast Aluminum AlSi9Cu3(Fe) Alloy

Abstract

High-pressure die casting (HPDC) is a widely used casting technology for product that is made of light metal such as aluminum alloy. During the die casting process, the molten metal is injected into a mold at high speed and solidified under high pressure. The amount of porosity in the cast part is an important question. Lots of technologies have been developed to minimize porosities, for example, vacuum-assisted high-pressure die casting process (VPDC). In this paper, AlSi9Cu3(Fe) aluminum alloy castings were produced by conventional HPDC with atmospheric venting and VPDC process under three different absolute cavity air pressures of 170 mbar, 90 mbar and 70 mbar at the cavity. The influence of absolute cavity air pressure on the porosity and on the mechanical properties of the castings was investigated and compared with conventional HPDC casting method. The results of the present study proved that the amount of porosity and the pore sizes in the castings can be significantly reduced from 1.10% at an atmospheric level to 0.47% at 70 mbar. This corresponds to 57% reduction. As a result, the mechanical properties are improved significantly, particularly, the tensile strength from 271.6 to 299.8 MPa, which corresponds to 10% increment and the elongation from 1.66 to 2.49%, which shows 50% increment. At lower absolute cavity air pressure, the entrapped gases become the final gas porosities in the die castings and show solidification shrinkage form inspected with scanning electron microscopy. In general, lower cavity air pressure contributes to reduce the pores, which improve the mechanical properties of die casting.