Additive for acidic zinc alloy plating bath, acidic zinc alloy plating bath and zinc alloy plating film

Abstract

The additive for an acidic zinc alloy plating bath according to the present invention is used for obtaining an acidic zinc alloy plating bath capable of obtaining a zinc alloy plating film with a good appearance and contains as active ingredients a glycine-containing water-soluble substance and an aliphatic polyamine whose carbon number is 12 or less. The glycine/polyamine ratio, which is a ratio of a glycine-equivalent molar concentration of the glycine-containing water-soluble substance to a molar concentration of the aliphatic polyamine, may be preferably 0.1 or more and 40 or less. The present invention also provides an acidic zinc alloy plating bath containing the above additive, and a zinc alloy plating film that is formed using the above acidic zinc alloy plating bath.

1 . An additive for an acidic zinc alloy plating bath, the additive containing as active ingredients a glycine-containing water-soluble substance and an aliphatic polyamine whose carbon number is 12 or less. 
     
     
         2 . The additive according to  claim 1 , wherein the aliphatic polyamine contains one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. 
     
     
         3 . The additive according to  claim 1 or 2 , wherein a glycine/polyamine ratio is 0.1 or more and 40 or less, wherein the glycine/polyamine ratio is a ratio of a glycine-equivalent molar concentration of the glycine-containing water-soluble substance to a molar concentration of the aliphatic polyamine. 
     
     
         4 . An acidic zinc alloy plating bath containing a bath-soluble zinc-containing substance, a bath-soluble metal-containing substance, and the active ingredients of the additive according to any one of  claims 1 to 3 . 
     
     
         5 . The acidic zinc alloy plating bath according to  claim 4 , wherein its pH is 4 or more and 6 or less. 
     
     
         6 . The acidic zinc alloy plating bath according to  claim 4 or 5 , wherein the acidic zinc alloy plating bath is boric acid-free. 
     
     
         7 . The acidic zinc alloy plating bath according to any one of  claims 4 to 6 , wherein the acidic zinc alloy plating bath is ammonia-free. 
     
     
         8 . The acidic zinc alloy plating bath according to any one of  claims 4 to 7 , wherein the acidic zinc alloy plating bath contains an acetic acid-containing substance. 
     
     
         9 . The acidic zinc alloy plating bath according to any one of  claims 4 to 8 , wherein
 the acidic zinc alloy plating bath contains a bath-soluble nickel-containing substance as the bath-soluble metal-containing substance, and   a co-deposition ratio of nickel in a zinc alloy plating film formed from the acidic zinc alloy plating bath is 5 mass % or more and 20 mass % or less.   
     
     
         10 . The acidic zinc alloy plating bath according to  claim 9 , wherein
 the acidic zinc alloy plating bath contains the bath-soluble nickel-containing substance, and   a glycine/nickel ratio is 0.1 or more, wherein the glycine/nickel ratio is a ratio of a glycine-equivalent molar concentration of the glycine-containing water-soluble substance to a nickel-equivalent molar concentration of the bath-soluble nickel-containing substance.   
     
     
         11 . The acidic zinc alloy plating bath according to any one of  claims 4 to 10 , wherein the acidic zinc alloy plating bath contains at least one of a primary brightener and a secondary brightener. 
     
     
         12 . A zinc alloy plating film of a zinc alloy plated member in which the zinc alloy plating film is formed on a member to be plated composed of an iron-based material, wherein when a depth profile of the zinc alloy plated member is measured, an alloying element-enriched region having a relatively high alloying element concentration is absent on a side proximal to the member to be plated in the zinc alloy plating. 
     
     
         13 . The zinc alloy plating film according to  claim 12 , wherein the zinc alloy plating film contains nickel as an alloying element and is formed from a plating bath that contains glycine and an aliphatic polyamine whose carbon number is 12 or less. 
     
     
         14 . The zinc alloy plating film according to  claim 12 or 13 , wherein
 when it is defined in the depth profile that a position closest to an outermost surface and having a zinc concentration of 60 mass % or more is a surface-side end portion of the zinc alloy plating film, a position at which the zinc concentration is equal to an iron concentration derived from the member to be plated is a member-side end portion of the zinc alloy plating film, and a length of a region from the surface-side end portion to the member-side end portion is a thickness of the zinc alloy plating film,   [Ni1] and [Ni2] satisfy Expression (1) below:   
       
         
           
             
               
                 
                   
                     
                       [ 
                       
                         Ni 
                         ⁢ 
                         1 
                       
                       ] 
                     
                     ≥ 
                     
                       [ 
                       
                         Ni 
                         ⁢ 
                         2 
                       
                       ] 
                     
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
       where [Ni1] is an average value of nickel concentration in an intermediate region represented by a range of 40% to 60% of the thickness of the zinc alloy plating from the surface-side end portion, and
 [Ni2] is a maximum value of nickel concentration in an initial region represented by a range between the member-side end portion and a position moved from the member-side end portion to the surface side by 30% of the thickness of the zinc alloy plating film.