Influence of alloying elements on wettability and reaction of molten aluminum with alumina

The effect of alloying elements on the wettability of molten aluminum to alumina substrate were investigated with the sessile drop method in a vacuum of 2 × 10^-3 Pa at temperatures from 973 K to 1173 K. The contact angle of molten aluminum on alumina substrate decreased from 109° to 92° as the temperature rose from 973 K to 1173 K. The alloying elements of 5.5%Cu, 15%Cu, 33%Cu, 1.1%Ni, 6%Ni, 10%Si, 0.15%Ti, 0.17%Be, 0.11%Zr and 0.47%Hf had little influence on the wettability to alumina. On the contrary, the addition of 4.1approx.9.7%Mg and 1.7approx.4.2%Li to molten aluminum lowered the contact angle by 10approx.20°. Higher the content of these elements more improved the wettability. Both Al-Li and Al-Mg alloys reacted with pure alumina in Ar atmosphere, and mass spectra and depth profile of positive secondary ions of Al⁺, Li⁺, Mg⁺, O⁺, LiAl⁺, LiAlO⁺, MgAl⁺, MgO⁺, etc. revealed that the 0.02approx.0.13 μm thick LiAlO₂ and MgAl₂O₄ were formed at the surface of alumina at 973 K. The thickness of LiAlO₂ layer increased proportionately to (reaction time) ^1/2 , the temperature and Li content, while the thin reaction layer of MgAl₂O₄ were almost unchanged even by longer holding until 3600 s at 1173 K.