A method of treating a surface of a stacked aluminum alloy ingot during a heating process. Spacer blocks are positioned adjacent aluminum alloy ingots to form a stack, wherein the spacer block has a support surface contacting a contact surface of the aluminum alloy ingot, and at least one of the support surface and the contact surface include a fluorine containing material. The stack is heated to at least a temperature at which the fluorine containing material decomposes or vaporizes such that a layer of a fluorinated oxide compound is formed at the interfaces between the ingots and the spacer blocks.