Patent ID: 8460534
Filing Date: 2013-06-11
Classification: C23C,C25D

Abstract:
1. A treatment solution for producing substantially chromium(VI)-free black conversion layers on zinc-containing alloy layers, the solution containing: at least one first carboxylic acid having 1 to 8 carbon atoms, the acid containing no polar groups with exception of the carboxylic group and being a monocarboxylic acid, at least one second carboxylic acid having 1 to 8 carbon atoms, comprising at least one further polar group that is selected from —OH, —SO 20 to 400 mmol/l Cr 50 to 2000 mmol/l NO and wherein the total concentration of carboxyl groups of the first carboxylic acid(s) is within a range of 5 to 150 mmol/l, the total concentration of carboxyl groups of the second carboxylic acid(s) is within a range of 5 to 150 mmol/l, the ratio of the concentration (in mol/l) of NO the following prerequisite is met: wherein, c(C1) is the total concentration (in mol/l) of carboxyl groups of the first carboxylic acid(s), c(C2) is the total concentration (in mol/l) of carboxyl groups of the second carboxylic acid(s), c(Cr c(NO