GB1121677A - Production of coloured aluminium-silicon alloys - Google Patents

Abstract

Articles of Al-Si alloy e.g. containing 1 to 13% Si of dark or black shade exhibiting coloured reflections are produced by including in the alloy a quantity of one or more elements capable of modifying the Al-Si eutectic and then anodizing the article obtained therefrom, e.g. using as electrolyte a bath of sulphuric acid, optionally containing oxalic, sulphosalicylic and/or citric acid, or in a chromic or an oxalic acid bath using D.C., A.C. or ripple current. The element added may be between 0.0005 and 0.1% Na, between 0.005 and 1% Sb, and/or 0.0003 and 0.1% S, by weight of the alloy, for producing in the black colour a slight maroon, blue or grey tinge respectively. The element may be introduced into the alloy melt as such, or as an alloy or compound. The alloy may additionally contain one or more of Ti e.g. 0.1%, Mg e.g. 0.5%, Mn, Cr, B and Zr, and impurities of Al such as Fe. The cast alloy ingots may be heated e.g. to 380 DEG C., extruded, forged, stamped, drawn or hot and cold rolled, then degreased with trichloroethylene, pickled in sulphochromic acid, rinsed and immersed in 15% HNO3 acid, prior to anodizing in a bath containing 200 g/l H2SO4 with C.D. of 1.5 A/dm2. After anodizing, the articles may be rinsed, flooded with boiling distilled water and brightened with bismuth oxychloride.