Short communicationThe influence of different vacuum degree on the porosity and mechanical properties of aluminum die casting

- Performance of the specimen changes with the vacuum degree.
- The quantity and shape change of pores with different vacuum degree.
- Relationship between mechanical properties and the quantity and shape of porosity.

AlSi9Cu3 alloy castings were produced by the vacuum-assisted high pressure die casting (HPDC) process under three different absolute pressures: 500 mbar, 200 mbar and 100 mbar. The influence of absolute pressure in the die cavity on the porosity, microstructure and mechanical properties of die castings were investigated. It shows that as the absolute pressure decreases, the average porosity and pore sizes reduce from 4.8% to 2.8%, 8.65 μm-5.61 μm respectively, and the tensile strength and elongation is improved markedly by 13%, 25.2% respectively. The specimens contain larger pores under higher absolute pressure. Meanwhile, it discovers that the shape of pores is also an important factor affecting the mechanical properties. The pores with sharp corner present are much more in the castings as the absolute pressure increases. As a whole, high vacuum degree contributes to reduce the porosity that would be the basis for subsequent heat treatment and improve mechanical properties.