Abstract: An aluminum alloy consising essentially of 0.65 to 0.75% by weight of magnesium and 0.50 to 0.60% by weight of silicon or 0.47 to 0.57% by weight of magnesium and 0.75 to 0.85% by weight of silicon, 0.15% to 0.25% by weight of iron, less than 0.05% of an impurity selected from the group consisting of copper, manganese, zinc, chromium, and titanium and the balance aluminum, the aluminum alloy being subjected to aging treatment at a temperature below 200.degree. C for 20 to 50 minutes to obtain 0.2% proof stress larger than 11 kg/mm.sup.2, ultimate tensile strength larger than 20 kg/mm.sup.2 and elongation more than 8%. Aluminum alloy shapes are formed of the above aluminum alloy by extrusion forming of the aluminum alloy to obtain an extrusion, coating a film on the surface of the extrusion with a water-soluble paint after forming thereon a ground film, heating the extrusion at a temperature below 200.degree.

Abstract: A method of forming an oxide film on the surface of an aluminum material by anodizing the aluminum material in an aqueous solution containing 0.5 to 10% by weight of oxalic acid and 0.05 to 1.0% by weight of sulfuric acid, in which either an electrolyzing voltage or the temperature of the aqueous solution is controlled in the range of 5 to 150V or 0.degree. to 40.degree. C, whereby the oxide film is colored in color tone from bronze to silver.

Abstract: A method of forming a colored oxide film on the surface of an aluminum material is disclosed in which the aluminum material is subjected to an electrolytic treatment in an aqueous solution containing sulfuric acid to form an aluminum oxide film containing aluminous oxides and having lattice defects; sulfuric ions in the solution are caused to enter into the lattice defects of the oxide film; some or all of the sulfuric ions are reduced to form sulfur and sulfides; and the colored oxide film is formed using the sulfur and sulfides as coloring sources.