Aqueous acidic immersion plating solutions and methods for plating on aluminum and aluminum alloys

A process for depositing a zinc alloy protective coating on aluminum or aluminum based alloy substrate which comprises

• (A) immersion plating the substrate by immersing the substrate in an aqueous acidic immersion plating solution having a pH of from about 4.5 to about 5.5 and comprising:
• from about 10 to about 30 g/l of zinc ions,
• from about 20 to about 50 g/l of nickel and/or cobalt ions,
• from about 0.5 to about 10 g/l of fluoride ions, and
• from about 0.005 to about 0.05 g/l of at least one inhibitor for a period of time sufficient to deposit the desired coating, and
• (B) removing the coated substrate from the immersion plating solution
• wherein the at least one inhibitor is a mercapto substituted nitrogen-containing heterocyclic compound and the zinc ions and the nickel and/or cobalt ions are provided with acetate as counter ion.

A process for depositing a zinc alloy protective coating on aluminum or aluminum based alloy substrate which comprises

• (A) immersion plating the substrate by immersing the substrate in an aqueous acidic immersion plating solution having a pH of from about 4.5 to about 5.5 and comprising:
• from about 1 to about 150 g/l of zinc ions,
• from about 5 to about 250 g/l of nickel and/or cobalt ions,
• from about 0.005 to about 100 g/l of fluoride ions provided the solution is free of cyanide ions, and
• from about 0.005 to about 100 g/l of at least one inhibitor for a period of time sufficient to deposit the desired coating, and
• (B) removing the coated substrate from the immersion plating solution,
• wherein the at least one inhibitor is a mercapto substituted nitrogen-containing heterocyclic compound and the zinc ions and the nickel and/or cobalt ions are provided with acetate as counter ion.