Wetting of pure aluminum and selected alloys on polycrystalline alumina and sapphire

Abstract

Using a modification of the dispensed drop method to measure true contact angles of readily oxidizing metals and alloys, the wettability of polycrystalline alumina and A-plane sapphire by pure aluminum and selected aluminum alloys was investigated. The experiments were performed under high vacuum in a horizontal tube furnace. The experimental setup produces a sessile drop free of its natural surface oxide layer minimizing flight time of the drop, and maintaining a drop impingement on the substrate. The experiments showed that there is no significant difference in the wettability of alumina and sapphire by aluminum as well as Al–11.5Si, Al–1Mg and Al–7Cu. On both substrates, aluminum shows a strong increase in contact angle well into the non-wetting regime just above the melting point. The wetting behavior of Al–7Cu on both substrates is slightly but significantly reduced in comparison to pure aluminum. The contact angles of Al–1Mg and Al–11.5Si remain rather constant between the respective liquidus temperatures of the alloys and 800 °C with θ (Al–1Mg) < θ (Al–11.5Si). Only Al–7Cu above 730 °C achieves the contact angle interval of 70–86° suggested to be most beneficial in terms of aluminum foam stabilization.