Combination colouring of aluminium alloys - using electrolyte contg. stannous or ferrous salts and immersion in heteropolyacids

• Main Authors: KELLER,JENS, KELLER,ERHARD, CHRISTOPHER GADDE,OVE
• Format: Patent
• Language: English; German
• Published: 10.06.1976
• Edition: 2
• Subjects: APPARATUS THEREFOR; CHEMISTRY; ELECTROFORMING; ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; METALLURGY; PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTIONOF COATINGS

Workpiece is oxidised anodically, stained electrolytically in an acid soln. of a metal salt which is more electronegative than Cu in electromotive series, using AC of 1-50 V for 0.1-15 min., then immersed in an aq. soln. of heteropolyacid of Si or P with Mo or W, without applying current, and sealed by standard methods. The electrolysis bath contains Cu salt or salts of other materials, which are more electropositive than Cu in electromotive series, and in addn., small quantities of another suitable metal salt, (I) e.g. Sn(II)-salts or salts of Ni, Co, Fe and Zn. (I) have a reducing activity on anions of heterpolyacids. Small particles of metal and (I) are built into oxide layer. On immersion into heteropolyacid soln. a colour change takes place which would not be caused by salt of Cu or more electropositive than Cr in electromotive series, and, in addn. small quantities of another suitable metal salt, (I), e.g. Sn(II)-salts or salts of Ni, Co, Fe and Zn. (I) have a reducing activity on anions of heteropolyacids. Sn all particles of metal of (I) are built into oxide layer. On immersion into heteropolyacid soln., a colour change takes place which would not be caused by salt of Cu or more electropositive metal alone.