Methods for inhibiting corrosion in brazed metal surfaces and coolants and additives for use therein

1. A method for inhibiting corrosion resulting from residual brazing flux remaining on a brazed metal surface in a cooling system, the method comprising:

contacting said brazed metal surface with a coolant consisting of:

a) a polycarboxylic acid functional compound having the structure:

 wherein R 1 , R 2 , R 3 , and R 4 are each independently selected from the group consisting of H, OH, COOH, C 1 -C 10 alkyl groups, glycol esters, anhydride groups, —COOM, and combinations thereof, wherein M is at least one of alkali metal ions, alkali earth metal ions, NH 4 + , amines, imidazoline, polyalcohol esters, C 1 to C 12 alkyl groups, and combinations thereof;

 with the proviso that at least two of R 1 , R 2 , R 3 , and R 4 contain an anhydride group, and at least one of R 1 , R 2 , R 3 , and R 4 contain the group —COOM, wherein M is defined above;

b) an azole compound;

c) an aliphatic or aromatic, mono- or dicarboxylic acid, or salts, isomers, or mixtures thereof;

d) a freezing point depressant; and

e) optionally, an additive selected from the group consisting of water, antifoam agents, colorants, dispersants, antiscalants, wetting agents, biocides, pH adjusting agents, buffering agents, and a combination thereof;

wherein the coolant lacks nitrate.

2. The method of claim 1 , wherein the polycarboxylic acid functional compound comprises a tall oil fatty acid derived from a cyclohexenoic acid containing compound.

3. The method of claim 2 , wherein the cyclohexenoic acid containing compound comprises a maleated tall oil fatty acid, a maleated tall oil fatty acid salt, a reaction product derived from a maleated tall oil fatty acid, a reaction product derived from a maleated tall oil fatty acid salt, a reaction product derived from a ethylene glycol ester, a reaction product derived from a ethylene glycol ester salt, or a maleated tall oil.

4. The method of claim 1 , wherein the polycarboxylic acid functional compound comprises a maleinized unsaturated fatty acid, an acrylate copolymer, a styrene copolymer, or a polymerizable acid graft polymer.

5. The method of claim 1 , wherein R 1 is a group having a structure (CH) x —(COO)—[(CH 2 ) y —O] z —H wherein: x is 0 to 10, y is from 1 to 5 and z is from 0 to 5.

6. The method of claim 1 wherein R 4 is a C 1 -C 10 alkyl group.

7. The method of claim 1 , wherein R 2 and R 3 comprise an anhydride group.

8. The method of claim 1 wherein the brazed aluminum surface comprises residual flux agent.

9. The method of claim 8 wherein the residual flux agent comprises halogen atoms.

10. The method of claim 9 wherein the halogen atoms are fluorine atoms.

11. The method of claim 8 wherein the residual flux agent comprises an alkaline metal halogen compound or an alkaline earth metal halogen compound.

12. The method of claim 11 wherein the residual flux agent comprises a mixture of K 3 AIF 5 , K 2 AIF 5 and KAIF 4 .

13. The method of claim 1 , wherein the azole compound is one or more of an alkyl benzotriazole, a thiazole, an imidazole, a tetrazole, or an indazole.

14. The method of claim 1 , wherein the azole compound is one or more of a tolyltriazole, methyl benzotriazole, butyl benzotriazole, or mercaptobenzotriazole.

15. The method of claim 1 , wherein the mono- or dicaraboxylic acid is a C 4 to C 12 mono- or dicaraboxylic acid.

16. The method of claim 1 , wherein the C 4 to C 12 mono- or dicaraboxylic acid is selected from the group consisting of 2-ethyl hexanoic acid, neodecanoic acid, benzoic acid, t-butylbenzoic acid, dodecandediodic acid, sebacic acid, salts thereof, isomers thereof, and mixtures thereof.

17. The method of claim 1 , wherein the carboxylic acid is a saturated aliphatic dicarboxylic acid.