Pre-treating aluminum surfaces with zirconium- and molybdenum-containing compositions

Abstract

Provided herein is a process for the pretreatment of workpieces having a surface of aluminum or aluminum alloys for noncutting forming and/or joining by welding or adhesive bonding to similarly pretreated, precoated workpieces, or to optionally precoated parts. The parts are composed of steel, galvanized steel, and/or alloy-galvanized steel. Further provided herein is a subsequent permanent corrosion-protecting treatment by phosphating, by means of a chromium-free conversion treatment, by application of primer, or by surface coating, where the workpieces are a) pickled by means of an aqueous, acidic solution comprising mineral acid by dipping or spraying, b) rinsed with water, and c) brought into contact with an aqueous, acidic, chromium-free solution including Zr as complex fluoride and Mo as molybdate by application by dipping or spraying. After subsequent drying, a layer weight from 2 to 15 mg/m 2 of Zr and Mo is formed.

1 . A process for the pretreatment of workpieces having a surface of aluminum or aluminum alloys for noncutting forming and/or joining by welding or adhesive bonding to pretreated workpieces, precoated workpieces, or precoated parts composed of steel and/or galvanized steel and/or alloy-galvanized steel, and also for a subsequent permanent corrosion-protecting treatment by phosphating, by means of a chromium-free conversion treatment, by application of primer or by surface coating, wherein the process comprises:
 a) pickling the workpieces using an aqueous, acidic solution comprising mineral acid by one of dipping and spraying;   b) rinsing the workpieces with water;   c) applying an aqueous, acidic, chromium-free solution to the workpieces by one of dipping and spraying, the solution comprising:
 Zr as complex fluoride, and 
 Mo as molybdate, 
 wherein a weight ratio, calculated as Zr/Mo metal, of Zr: Mo is from 15:1 to 3.5:1, and 
 wherein the solution includes from 100 to 800 mg/l of Zr and from 30 to 100 mg/l of Mo, calculated as Zr/Mo metal, and has a pH from 2.5 to 4.5; and 
   d) drying the workpieces, wherein, after the drying, a layer weight is provided on each workpiece of from 2 to 15 mg/m 2  of Zr and Mo.   
     
     
         2 . The process according to  claim 1 , wherein the aqueous, acidic, chromium-free solution in step c) comprises Zr as complex fluoride and Mo as molybdate in the weight ratio, calculated as Zr/Mo metal, of Zr: Mo of from 13:1 to 7:1. 
     
     
         3 . A process for the pretreatment of workpieces having a surface of aluminum or aluminum alloys for noncutting forming and/or joining by welding or adhesive bonding to pretreated workpieces, precoated workpieces, or precoated parts composed of steel, galvanized steel, and/or alloy-galvanized steel, and also for a subsequent permanent corrosion-protecting treatment by phosphating, by means of a chromium-free conversion treatment, by application of primer or by surface coating, wherein the process comprises:
 a) pickling the workpieces using an aqueous, acidic solution comprising mineral acid by dipping or spraying;   b) rinsing the workpieces with water;   c) applying an aqueous, acidic, chromium-free solution to the workpieces dipping or spraying, the solution comprising:
 Zr as complex fluoride, and 
 Mo as molybdate, 
 wherein a weight ratio, calculated as Zr/Mo metal, of Zr: Mo is from 2:1 to 1:2, and 
 wherein the solution includes from 0.4 to 7.5 g/l of Zr and from 0.4 to 7.5 g/l of Mo, calculated as Zr/Mo metal, and has a pH from 1.0 to 3.0; and 
   d) drying the workpieces, wherein, after the drying, a layer weight is provided on each workpiece of from 2 to 15 mg/m 2  of Zr and Mo.   
     
     
         4 . The process according to  claim 3 , wherein the aqueous, acidic, chromium-free solution in step c) comprises Zr as complex fluoride and Mo as molybdate in the weight ratio, calculated as Zr/Mo metal of Zr:Mo of from 1.4:1 to 1:1.4. 
     
     
         5 . The process according to  claim 1 , wherein the aqueous, acidic, chromium-free solution in step c) further comprises at least one polymer selected from the group consisting of poly(meth)acrylic acid, (meth)acrylic acid copolymers, polyvinylphosphonic acid, vinylphosphonic acid copolymers, and maleic acid copolymers. 
     
     
         6 . The process according to  claim 5 , wherein the at least one polymer is polyacrylic acid and/or an acrylic acid-maleic acid copolymer. 
     
     
         7 . The process according to  claim 1 , wherein the workpieces are pickled using a solution comprising surfactant, hydrofluoric acid, and sulfuric acid. 
     
     
         8 . The process according to  claim 7 , wherein the workpieces are pickled using the solution further comprising from 3 to 8 g/l of the sulfuric acid, from 50 to 150 mg/l of free fluoride, and from 1 to 3 g/l of a nonionic surfactant. 
     
     
         9 . The process according to  claim 1 , further comprising pretreating the workpieces for noncutting forming, the pretreating comprising applying a lubricant before the noncutting forming. 
     
     
         10 . The process according to  claim 1 , wherein said cleaning and said rinsing are carried out before said corrosion-protecting. 
     
     
         11 . An aqueous acidic solution for the pretreatment of workpieces having a surface of aluminum or aluminum alloys, wherein the solution is chromium-free and comprises Zr as complex fluoride and Mo as molybdate in a weight ratio calculated as Zr/Mo metal of Zr:Mo of from 15:1 to 3.5:1, and wherein the solution further comprises from 100 to 800 mg/l of Zr and from 30 to 100 mg/l of Mo calculated as Zr/Mo metal and has a pH of from 2.5 to 4.5. 
     
     
         12 . A concentrate from which a solution according to  claim 11  is obtainable by dilution with water or an aqueous solution. 
     
     
         13 . An aqueous acidic solution for the pretreatment of workpieces having a surface of aluminum or aluminum alloys, wherein the solution is chromium-free and comprises Zr as complex fluoride and Mo as molybdate in a weight ratio calculated as Zr/Mo metal of Zr:Mo of from 2:1 to 1:2, and wherein the solution further comprises from 0.4 to 7.5 g/l of Zr and from 0.4 to 7.5 g/l of Mo calculated as Zr/Mo metal and has a pH of from 1.0 to 3.0. 
     
     
         14 . A concentrate from which a solution according to  claim 13  is obtainable by dilution with water or an aqueous solution. 
     
     
         15 . A workpiece comprising a surface of aluminum or aluminum alloys, wherein the workpiece has been pretreated by means of a process according to  claim 1 . 
     
     
         16 . The process according to  claim 10 , further comprising applying an activation treatment prior to said corrosion-protecting. 
     
     
         17 . The concentrate according to  claim 12 , wherein the solution is further obtainable through the adjustment of pH. 
     
     
         18 . The concentrate according to  claim 14 , wherein the solution is further obtainable through the adjustment of pH.