Patent Publication Number: US-2005142294-A1

Title: Method of applying the coatings from aluminum alloy on cast iron and steel products

Description:
TECHNICAL FIELD  
      The invention refers to applying metal, e.g. aluminum, coatings by plunging into the melt and may be used, for instance, for corrosion protection of rolled and other cast iron and steel products.  
     BACKGROUND OF THE INVENTION  
      Methods of applying the aluminum coatings on steel products by plunging into the aluminum melt comprising zinc and magnesium are known.  
      The closest analog of the present invention is the method of applying the aluminum coatings on cast iron and steel products comprising product surface preparation and consequent plunging the product into the aluminum melt alloyed with zinc and silicon (GB, No 1440328, MPK C23 C1/00,1976).  
      The disadvantage of the closest analog is impossibility of aluminum melt applying on cast iron and steel products at the temperature lower than 715° C. without using fluxes and the presence of intermetallic compounds of quite a big thickness (10-15 micrometers) make the coating brittle, which doesn&#39;t allow to deform the steel product with aluminum coating hereinafter.  
    
    
     SUMMARY OF THE INVENTION  
      The present invention solves the problem of decreasing the temperature of aluminum melt, at this temperature the formation of quite a plastic protective coating without using the flux is provided, which allows to deform rolled and other products with aluminum coatings.  
      In the method of applying the aluminum coatings on cast iron and steel products comprising product surface preparing and consequent plunging the product into the aluminum melt alloyed with zinc and silicon the solution of said problem is reached by jet-abrasive preparing of the product and the aluminum melt is alloyed with zinc, silicon, magnesium, tin of following mass percentage:  
                                                      zinc    7.0-10.0           silicon   3.0-5.0           magnesium   0.5-1.5           tin   0.2-0.5                      
 
 while the temperature of the melt is in the range of 660-680° C. 
 
      The results of applying the aluminum coatings, using jet-abrasive preparing of the surface, in melts of different chemical composition, studying the structure and working qualities of the coatings are presented in Table 1.  
      Plasticity of the coatings was estimated by testing the pattern on bending around the cylindrical mandrel, while wending on which the coating on the pattern doesn&#39;t break. Corrosion qualities of the coatings were estimated according to the results of fast tests of patterns treaded with moisture phase film comprising C1-ion (imitation of the sea atmosphere).  
      Electrochemical studies of the resulting coating have shown that alloying the aluminum melt, comprising zinc, silicon, magnesium and tin leads to significant increasing in reproducibility of results of electrode potential measurement of the coating, which indicate high uniformity of chemical composition of coating surface layers.  
      Aluminum coatings were applied on patterns after the jet-abrasive preparing of their surface under different temperature and time regimes by plunging into the melt of the following chemical composition: aluminum—base, zinc—8.0%, silicon—4.5%, magnesium—1.1%, tin—0.4%. The results of the studies if said coatings are presented in Table 2.  
      The studies have shown that in temperature range of 660-680° C. the formation of thickness uniform aluminum coating without flux using is taking place, this coating is characterized by high corrosion resistance and plasticity.  
      Analysis of the results of aluminizing in melts of different chemical composition and of different regimes (Tables 1,2) has shown that aluminizing of steel patterns with jet-abrasive preparing of surface in the melt comprising aluminum—base, zinc—7.0-10.0%, silicon—3.0-5.0%, magnesium—0.5-1.5%, tin—0.2-0.5% at the temperature of 660-680° C. leads to the solution of the above said problem. Aluminizing in the proposed melt without flux using and by said regimes provides formation of thickness and structure uniform plastic coatings of high corrosion resistance.  
               TABLE 1                          The main characteristics of aluminum coatings formed in       melts of different chemical composition.                                                 Time of       Transition   Minimum                   exposure in   Coating   zone   diameter of   Character           Temperature   the melt,   thickness,   thickness,   mandrel,   of the       Melt composition   of applying, C.   sec   micrometer   micrometer   mm   corrosion                                                 Aluminum - base   720-740   40   70   50   —   Pit       Silicon - 2.0%       Manganese - 0.5%       Aluminum - base   730-750   70   40   20   20   Pit       Silicon - 7.0%       Manganese - 0.5%       Aluminum - base   690-710   60   50   25   15   General,       Zinc - 5.0%                       local       Silicon - 2.0%       Aluminum - base   680-700   60   70   20   10   General,       Zinc - 7.0%                       local       Silicon - 5.0%       Aluminum - base   670-690   70   60   20   10   General,       Zinc - 10%                       local       Silicon - 5.0%       Aluminum - base   660-680   70   70   10   10   General       Zinc - 10%       Silicon - 5.0%       Magnesium - 1.0%       Aluminum - base   660-680   70   70   5   10   General       Zinc - 10%       Silicon - 5.0%       Magnesium - 1.0%       Tin - 0.5%                  
 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                   
               
               
                 The main characteristics of aluminum coatings formed 
               
               
                 in the melt of proposed chemical composition. 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 Time of 
                   
                 Transition 
                 Minimum 
                   
               
               
                   
                 Temperature 
                 exposure in 
                 Coating 
                 zone 
                 diameter of 
                 Character 
               
               
                 Melt  
                 of 
                 the melt, 
                 thickness, 
                 thickness, 
                 mandrel, 
                 of the 
               
               
                 composition 
                 applying, C. 
                 sec 
                 micrometer 
                 micrometer 
                 mm 
                 corrosion 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Aluminum - base 
                 650 
                 120 
                 80 
                 10 
                 15 
                 General 
               
               
                 Zinc - 8.0% 
                 660 
                 80 
                 70 
                 5 
                 10 
                 General 
               
               
                 Silicon - 4.5% 
                 670 
                 70 
                 60 
                 5 
                 10 
                 General 
               
               
                 Magnesium - 1.1% 
                 680 
                 70 
                 60 
                 5 
                 10 
                 General 
               
               
                 Tin - 0.4% 
                 690 
                 70 
                 70 
                 10 
                 20 
                 Local 
               
               
                   
                 700 
                 70 
                 70 
                 15 
                 25 
                 Local 
               
               
                   
                 710 
                 80 
                 90 
                 20 
                 30 
                 Local