Abstract: A caustic etchant composition suitable for use on lithium containing aluminum alloys has between about 125 to 300 grams per liter of sodium hyroxide, between about 35 to 145 grams per liter of sodium sulfide, between about 0.5 to 4 percent by volume of triethanolamine, between about 1 to 10 grams per liter EDTA, between about 2 to 20 grams per liter sodium carbonate and the balance being water. The composition is effective to chemically etch lithium containing aluminum alloys and leave a smooth, clean chemically milled surface effective for use in chemically milled parts and free of stress concentrating surface characteristics.

Abstract: This application involves a continuous process for chemical milling of aluminum by recovering caustic from an etch tank solution by treating the solution having dissolved metals and other contaminants with calcium oxide and barium compounds to form precipitates which are separated by centrifugation to permit recovery and reuse of the caustic.

Abstract: An etchant composition suitable for use with a wide variety of steel compositions contains between about:______________________________________ 10-300 ml 75% H.sub.3 PO.sub.4 100-700 ml HNO.sub.3 (42.degree. Baume) 80-100 ml HF (70%) 1-50 gm NaNO.sub.3 10-100 gm Urea 1-30 gm Sodium Benzoate 5-200 gm Dissolved Iron or Steel Balance Water ______________________________________The composition is very fast acting etchant compared to prior etchants. The etchant has a very uniform etch rate leaving smooth etched surfaces, including over fillets and similar structures. The etchant is thus particularly suitable for chemical milling of steels and parts fabricated of steels.

Abstract: A process of continuously chemically milling refractory metals, e.g., titanium using a supersaturated milling solution which form a water soluble precipitate, milling at temperatures of 140.degree.-160.degree. F., and using two chemical milling tanks so that the milling solution is pumped from one to the other when the precipitate builds up in the first tank to a predetermined level. The water soluble precipitate is easily and inexpensively disposed of and the process makes more efficient use of chemicals.

Abstract: A process and compositions for detecting improperly processed areas in heat treated aluminum are disclosed. A solution containing an acid or a base and an oxidizing agent and, if desired, a color enhancing ingredient is applied to an aluminum object to produce a color difference between those areas of the surface of the object which have been properly hardened and the areas resulting from improper heat treatment. The solution can be applied to the aluminum by brushing, swabbing, immersion or spraying. The acid or base in the solution attack the aluminum surface so that the oxidizing agent in the solution can react with the aluminum to produce the aforementioned color differential.

Abstract: An improved composition and process for chemically milling titanium, refractory metals, and their alloys, resulting in decreased absorption of hydrogen, thus allowing chemical milling of beta titanium and alpha beta titanium, which normally cannot be chemically milled in conventional chemical milling solutions because of hydrogen embrittlement.The chemical milling solution itself consists of a mixture of nitric acid; hydrofluoric acid or fluoride salts; derivatives of carbonic acid, such as carbamide; derivatives of monocarboxylic acids containing alkali metal ions, such as sodium benzoate; and a source of sodium ions compatible with the remainder of the composition, preferably sodium nitrate.The addition of sodium benzoate results in a more uniform metal removal rate, thus permitting the producing of high precision parts.

Abstract: This application describes a composition and a process of chemically milling refractory metals and their alloys. The composition comprises a combination of nitric acid, hydrofluoric acid, and phosphoric acid, and preferably includes a derivative of carbonic acid, such as carbamide. The composition is particularly useful in the chemical milling of beta titanium, alpha beta titanium, and alpha titanium alloys. Use of the composition of this invention results in reduced tolerances in the chemically milled article and also reduced hydrogen absorption in the titanium part which is chemically milled.