Method of coating articles of aluminum and an electrolytic bath therefor

A method of coating aluminum and aluminum alloys predominating in aluminum with a hard, adherent, smooth, uniform and corrosion-resistant coating, which method comprises immersing aluminum or its said alloy in an aqueous electrolytic solution in a container in which said aluminum or its said alloy serves as the anode and said container serves as the cathode, said aqueous electrolytic solution comprising an alkali metal silicate, a peroxide, a water-soluble carboxylic group-containing organic acid and a water-soluble fluoride, applying an electrical voltage potential between said electrodes, raising said voltage to about 300 volts within about 1 to about 5 seconds, and thereafter gradually raising said voltage to about 450 volts over a period of a few minutes until the desired coating thickness is formed.

An electrolytic bath for forming a coating on the surface of aluminum and alumimun alloys predominating in aluminum, said electrolytic bath consisting essentially of an aqueous solution containing from about 1 to about 200 cm.sup.3 per liter of an alkali metal silicate, from about 1 to about 20 grams per liter of a peroxide, from about 1 to about 30 cm.sup.3 per liter of a water-soluble carboxylic group-containing organic acid and from about to about 30 cm.sup.3 per liter of a water-soluble fluoride.

A method of coating aluminum and aluminum alloys predominating in aluminum with a hard, adherent, smooth, uniform and corrosion-resistant coating, which method comprises immersing the aluminum or its said alloy in an aqueous electrolytic solution comprising hydrofluosilicic acid, a peroxide, a water-soluble carboxylic group-containing organic acid and a water-soluble fluoride, said aluminum or its alloy serving as the anode, immersing a second metal in said electrolytic solution in which said second metal serves as the cathode, applying an electrical voltage potential between said electrodes, raising said voltage to about 300 volts within about 1 to about 5 seconds, and thereafter gradually raising said voltage to about 450 volts over a period of a few minutes until the desired coating thickness is formed.

A method of coating aluminum and aluminum alloys predominating in aluminum with a hard, adherent, smooth, uniform and corrosion-resistant coating, which method comprises immersing aluminum or its said alloy in an aqueous electrolytic solution in a container in which said aluminum or its said alloy serves as the anode and said container serves as the cathode, said aqueous electrolytic solution comprising hydrofluosilicic acid, a peroxide, a water-soluble carboxylic group-containing organic acid and a water-soluble fluoride, applying an electrical voltage potential shock between said electrodes, raising said voltage to about 300 volts within about 1 to about 5 seconds, and thereafter gradually raising said voltage to about 450 volts over a period of a few minutes until the desired coating thickness is formed.

An electrolytic bath for forming a coating on the surface of aluminum and aluminum alloys predominating in aluminum, said electrolytic bath consisting essentially of an aqueous solution containing from about 1 to about 200 cm.sup.3 per liter of hydrofluosilicic acid, from about 1 to about 20 grams per liter of a peroxide, from about 1 to about 30 cm.sup.3 per liter of a water-soluble carboxylic group-containing organic acid and from about to about 30 cm.sup.3 per liter of a water-soluble fluoride.

An electolytic bath for forming a coating on the surface of aluminum and aluminum alloys predominating in aluminum, said electrolytic bath consisting essentially of an aqueous solution of an alkali metal silicate, a peroxide, a carboxylic group-containing organic acid and a water-soluble fluoride.