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 die casting process the molten metal is injected into a mold at high speed and solidify 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 were 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 MPa 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 shows 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.

Study of mechanical properties of the YL113 die casting surface and middle layer

“…Wang et al [6] found through their research on fatigue fracture of die-casting parts that 98.5% of fatigue crack sources in die-casting alloys originate from internal pores in the castings; Koch et al [7] have shown that the fatigue crack source of die-casting alloys is located at the edge of the void defect near the center of the specimen, and the crack grows outward during tension. After studying the relationship between internal defects and the casting performance of diecasting parts, Szalva et al [8][9] found that the differences in mechanical properties of die-casting parts are caused by different areas of high concentrations of gas pores in the specimens, and gas shrinkage is the main factor affecting the elongation of die-casting alloy. Easton et al [10] found that tensile fracture cracks are generated along grain boundaries, and they mostly occur near the surface defect zone of the casting.…”

Detection of Porosity in Impregnated Die-Cast Aluminum Alloy Piece by Metallography and Computer Tomography

“…The change in crystallization volume and the degree of gas porosity and air entrapment can be compensated for with a variety of die-casting processes (e.g., melt treatment, postpressure, post-compression). With these methods, porosity can be reduced to 0.2-0.5% in quality casting [3][4][5]. This amount of porosity is unacceptable where gas permeability is not allowed.…”