アルミニウム合金溶湯の酸化に及ぼす合金元素の影響

抄録

  Binary Al-2 to 12%Cu, Al-2 to 12%Si, Al-2 to 6%Mn and Al-2 to 6%Zn alloys were held at temperatures 650°C to 900°C for 3 hr. The oxidation weight gain was measured and the extracted oxides were X-ray diffracted. Oxidation of molten aluminum advances slightly when the melt is held in the air at temperatures below 800°C and considerably at 850°C or above. Cu and Mn suppress oxidation of molten aluminum slightly at 750°C or below and considerably at 850°C or above. Si up to 4%, suppress the oxidation at 850°C or above, but Si 4 to 12% slightly promotes the oxidation. Zn suppresses the oxidation at 750°C or below but remarkably promotes the oxidation at 850°C or above. These oxidation phenomena of molten aluminum mainly relates with a transformation of the surface oxide layer from γ-Al₂O₃ to α-Al₂O₃. A Si oxide has an influence on oxidation of molten aluminum containing Si4% or more. Remarkable oxidation of Al-Zn alloys is attributed to vaporizing of Zn.