An aluminum alloy article is cleaned to remove oxides and organic matter from a coatable surface, coated with a composition comprising an organic resin and a fluorine compound, and then heated to an elevated temperature to decompose the organic resin and at least a portion of the fluorine compound. After heating the coated surface is left with a protective oxyfluoride film that prevents blistering and hydrogen pickup and promotes hydrogen degassing from the article.

Aluminum alloys, such as aluminum-magnesium alloys are commonly subjected to various heat treatments in their processing. Abbe, in U.S. Pat. No. 2,379,467, recognized in 1945 that such heat treatment can cause surface blistering. Abbe solved this problem by cleaning aluminum alloy forgings with lye and nitric acid solution, and then wetting them with a water solution of sodium fluorborate, and then drying the forgings before heat treatment. Even earlier, Stroup, in U.S. Pat. No. 2,092,033, recognized that there was a greater susceptibility to blistering where the atmosphere surrounding the aluminum contained constituents such as water vapor, ammonia or sulfur compounds and where the aluminum was alloyed with magnesium in combination with copper, nickel, silicon and/or zinc. Stroup found that most blistering occurred at temperatures over about 427.degree. C. (801.degree. F.)--above the usual range employed for annealing cold worked aluminum alloys. Stroup's solution to eliminate blistering was to provide a protective atmosphere containing vaporous fluorine-bearing compounds, based on the volume of the heating furnace. The fluorine constituent was added to the furnace atmosphere either by heating solid fluorine-containing salts in the furnace or by introducing vaporous fluoride such as hydrogen fluoride, boron fluoride, or low molecular weight or low carbon number fluorinated aliphatic hydrocarbons in gaseous form. In the former case, the solid materials may be deposited on the floor of the furnace or in some container and allowed to vaporize or decompose under the influence of heat. Certain fluorides, calcium fluoride, sodium fluoride and potassium fluoride, were not found to be effective, however. In U.S. Pat. No. 2,380,202 (Stroup) the beneficial effect of a fluorine-containing atmosphere was improved, for alloys containing at least 70% magnesium, by incorporating calcium or beryllium into the alloy and using an atmosphere of HF, BF.sub.3, organic fluoride gases and dry carbon dioxide rather than air. Stroup, in U.S. Pat. No. 2,092,034 deliberately applied an artificial oxide coating to aluminum alloys before subjecting the alloy to thermal treatment, as a means to control high temperature blistering. These vapors could however cause corrosion problems in furnaces over a long period of time. In a subsequent article "Atmospheric Control In The Heat Treatment Of Aluminum Products", P. T. Stroup, Controlled Atmospheres, October 1991, pp. 207-220, American Society for Metals, Cleveland, Ohio, Stroup further discussed and illustrated blistering and voids in cross-sectional views caused by heating aluminum sheet in air containing as little as 0.0012% total sulfur.