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: This disclosure concerns a process for increasing the etch rate of an aluminum and aluminum alloy chem-milling composition while increasing the tank life of the composition by adding sodium nitrate to a composition containing sodium hydroxide as the principal active ingredient.