Degassing of aluminum alloys during re-melting

The evolution of porosity during re-melting of near-eutectic casting Al alloys has been investigated in-situ using X-ray micro-focus radiography. During re-melting process, gas bubbles float out of the melt quickly when the liquid melt interface passes through them. Based on the degassing phenomenon from the real-time observation, several re-melting experiments were carried out with pure aluminum and a hypoeutectic Al-7%Si-0.4%Mg (A356) in addition to the near-eutectic Al-13%Si alloys. The results clearly show that the area fraction of porosity in the final Al castings decreases dramatically after re-melting one or two times, of which the mechanism is discussed in this paper.

► Evolution of porosity during re-melting of Al alloys has been investigated.
► Gas bubbles float out of the melt quickly during re-melting process.
► Area fraction of porosity in Al castings decreases dramatically after re-melting.
► Re-melting process has been developed for degassing in aluminum alloys.