Environmentally friendly aluminum coatings as sacrificial coatings for high strength steel alloys

Abstract

Electroplating process is described for coating a ferrous alloy steel cathode substrate with an aluminum coating, the process comprises: a) immersing an aluminum anode substrate in a plating bath formulation comprising: a source of aluminum, an ionic liquid, a brightening agent, and a metal-salt compound; b) etching the cathode substrate by immersing it into the aluminum plating bath and conducting an anodic polarization step; c) electroplating the etched cathode substrate with the aluminum plating bath formulation; and d) rinsing with alcohol and water, and drying. Preferably, the process further comprises a heat treatment applied to the aluminum coated ferrous steel alloy obtained in step d).

1 . An electroplating process for coating a ferrous alloy steel cathode substrate with an aluminum coating, characterised in that the process comprises:
 immersing an aluminum anode substrate in an aluminum plating bath formulation comprising:
 a source of aluminum, 
 an ionic liquid, 
 a brightening agent, and 
 a metal salt; 
   etching a ferrous steel alloy cathode substrate by immersing it into the aluminum plating bath formulation and performing an anodic polarization;   electroplating the etched ferrous alloy steel cathode substrate with the aluminum plating bath formulation, to form an aluminum coated ferrous steel alloy, wherein electroplating is carried out with a current density ranging from 1 mA/cm 2  to 100 mA/cm 2 , at a temperature ranging from 20° C. to 100° C. and under a dry inert gas; and   rinsing the aluminum coated ferrous steel alloy.   
     
     
         2 . The electroplating process of  claim 1 , wherein the ferrous alloy steel is a high strength steel alloy. 
     
     
         3 . The electroplating process of  claim 1 , wherein the source of aluminum is an aluminum halide. 
     
     
         4 . The electroplating process of  claim 1 , wherein the ionic liquid is a nitrogen-containing compound selected from N-alkyl-pyridinium salts, N-alkyl-N′-alkyl′ imidazolium salts, N-alkyl-N-alkyl′ pyrrolidinium salts, N-alkyl-N-alkyl′ piperidinium salts, quaternary ammonium salts and combinations thereof. 
     
     
         5 . The electroplating process of  claim 4 , wherein the counter-anion of the nitrogen-containing compound is a halide, and the cation is selected from N-alkyl-N′-alkyl′ imidazolium (I) and N-alkyl-N-alkyl′ pyrrolidinium (II), wherein the substituents R and R′ independently represent an alkyl group. 
       
         
           
           
               
               
           
         
       
     
     
         6 . The electroplating process of  claim 1 , wherein the brightening agent is selected from the group consisting of 1,10-phenanthroline, phthalazine, saccharin, isoniazid, coumarin, isonicotinic acid, nicotinic acid, 3,4-(methylenedioxy)toluene, 1,4-butynediol, 2-aminothiazole, 2-mercaptothiazoline, 1-methylimidazole and combinations thereof. 
     
     
         7 . The electroplating process of  claim 1 , wherein the metal salt is an alkali-metal halide. 
     
     
         8 . The electroplating process of  claim 1 , wherein the aluminum plating bath formulation consists of:
 from 95.30 to 99.95 wt % of a mixture of aluminum trichloride and 1-ethyl-3-methylimidazolium chloride, wherein both components are present in the mixture in a molar ratio ranging from 80:40 to 60:40;   from 0.01 to 1.0 wt % of 1,10-phenanthroline; and   from 0.04 to 3.7 wt % of KCl.   
     
     
         9 . The electroplating process of  claim 1 , wherein the electroplating step is carried out with a current density ranging from 5 mA/cm 2  to 25 mA/cm 2 , a temperature ranging from 40° C. to 75° C. and stirring the electrolyte at a range from 500 rpm to 1000 rpm. 
     
     
         10 . The electroplating process of  claim 1 , wherein an aluminum anode substrate is subject to a pre-treatment step comprising:
 mechanical polishing an aluminum anode substrate;   alkaline cleaning the polished aluminum substrate followed by water rinsing;   deoxidizing the cleaned aluminum substrate followed by water rinsing; and   drying the deoxidized aluminum substrate to obtain a polished, clean, deoxidized and dry aluminum anode substrate.   
     
     
         11 . The electroplating process of  claim 1 , wherein the ferrous alloy steel cathode is subject to a pre-treatment comprising:
 degreasing an steel alloy substrate, and   dry-blasting the degreased steel alloy, followed by removing any powder remaining in the surface of the stripped steel alloy to obtain a degreased and blasted ferrous steel alloy cathode substrate.   
     
     
         12 . The electroplating process of  claim 1 , further comprising heat treating the aluminum coated ferrous steel alloy. 
     
     
         13 . The electroplating process of  claim 12 , further comprising applying a conversion coating to the aluminum coated ferrous steel alloy obtained by the heat treating or the rinsing, wherein the conversion coating is selected from a hexavalent chromium conversion coating or a chromium free conversion coating. 
     
     
         14 . An aluminum coated ferrous steel alloy obtained by:
 immersing an aluminum anode substrate in an aluminum plating bath formulation comprising:
 a source of aluminum, 
 an ionic liquid, 
 a brightening agent, and 
 a metal salt; 
   etching a ferrous steel alloy cathode substrate by immersing it into the aluminum plating bath formulation and performing an anodic polarization;   electroplating the etched ferrous alloy steel cathode substrate with the aluminum plating bath formulation, to form an aluminum coated ferrous steel alloy, wherein electroplating is carried out with a current density ranging from 1 mA/cm 2  to 100 mA/cm 2 , at a temperature ranging from 20° C. to 100° C. and under a dry inert gas; and   rinsing the aluminum coated ferrous steel alloy.   
     
     
         15 . Use of the aluminum coated ferrous steel alloy of  claim 14  in aeronautical, automotive, marine, construction, industrial and household applications. 
     
     
         16 . An aluminum plating bath formulation comprising:
 an aluminum halide;   a nitrogen-containing compound selected from N-alkyl-N′-alkyl′ imidazolium halide or N-alkyl-N-alkyl′ pyrrolidinium halide;   a brightening agent; and   an alkali metal halide.   
     
     
         17 . The aluminum plating bath formulation of  claim 16 , comprising:
 from 95.30 to 99.95 wt % of a mixture of aluminum trichloride and 1-ethyl-3-methylimidazolium chloride, wherein both components are present in the mixture in a molar ratio ranging from 80:40 to 60:40,   from 0.01 to 1.0 wt % of 1,10-phenanthroline, and   from 0.04 to 3.7 wt % of KCl.