Corrosion-resistant a1-based structural member and method for manufacture thereof

Abstract

A corrosion-resistant Al-based structural member ( 1 ) is provided that has a base layer ( 2 ) adhered to the surface of an Al-based structural member ( 1 0 ), and a corrosion-inhibiting coating ( 3 ) adhered to the surface of the base layer ( 2 ). The base layer ( 2 ) is made of Zn, and the corrosion-inhibiting coating ( 3 ) is made of a trivalent Cr-containing chromate coating for Zn. It is thereby possible to provide a corrosion-resistant Al-based structural member equipped with a nonpolluting corrosion-inhibiting coating containing no hexavalent chromium.

1 . A corrosion-resistant Al-based structural member comprising a base layer ( 2 ) adhered to the surface of an Al-based structural member ( 1   0 ), and a corrosion-inhibiting coating ( 3 ) adhered to the surface of the base layer ( 2 ), the base layer ( 2 ) comprising Zn, and the corrosion-inhibiting coating ( 3 ) comprising a trivalent Cr-containing chromate coating for Zn.  
   
   
       2 . A process for producing a corrosion-resistant Al-based structural member, the process comprising a step of forming a base layer ( 2 ) comprising Zn on the surface of an Al-based structural member ( 1   0 ) by a zincate treatment, and a step of forming a corrosion-inhibiting coating ( 3 ) comprising a trivalent Cr-containing chromate coating for Zn on the surface of the base layer ( 2 ) by a chromate treatment using a trivalent chromate agent.  
   
   
       3 . The process for producing a corrosion-resistant Al-based structural member according to  claim 2 , wherein a treatment time t 1  required for the zincate treatment is set at a value that enables the amount of Zn deposited on the surface of the Al-based structural member ( 1   0 ) to be increased to give the base layer ( 2 ) comprising Zn having a required thickness, and a treatment time t 2  required for the chromate treatment is set at a value that enables the trivalent Cr-containing chromate coating for Zn to be reliably formed on the surface of the base layer ( 2 ) while ensuring the thickness of the base layer ( 2 ), despite the base layer ( 2 ) being dissolved by the chromate treatment.  
   
   
       4 . The process for producing a corrosion-resistant Al-based structural member according to  claim 3 , wherein the treatment time t 1  required for the zincate treatment is ≧30 s, and the treatment time t 2  required for the chromate treatment is ≦15 s.  
   
   
       5 . A corrosion-resistant Al-based structural member comprising a base layer ( 2 ) adhered to the surface of an Al-based structural member ( 1   0 ), and a corrosion-inhibiting coating ( 3 ) adhered to the surface of the base layer ( 2 ), the base layer ( 2 ) comprising Zn, and the corrosion-inhibiting coating ( 3 ) comprising a trivalent Cr-containing chromate coating.  
   
   
       6 . A process for producing a corrosion-resistant Al-based structural member, the process comprising a step of forming a base layer ( 2 ) comprising Zn on the surface of an Al-based structural member ( 1   0 ) by a zincate treatment, and a step of forming a corrosion-inhibiting coating ( 3 ) comprising a trivalent Cr-containing chromate coating on the surface of the base layer ( 2 ) by a chromate treatment using a trivalent chromate agent.  
   
   
       7 . The process for producing a corrosion-resistant Al-based structural member according to  claim 6 , wherein a treatment time t 1  required for the zincate treatment is set at a value that enables the amount of Zn deposited on the surface of the Al-based structural member ( 1   0 ) to be increased to give the base layer ( 2 ) comprising Zn having a required thickness, and a treatment time t 2  required for the chromate treatment is set at a value that enables the trivalent Cr-containing chromate coating to be reliably formed on the surface of the base layer ( 2 ) while ensuring the thickness of the base layer ( 2 ), despite the base layer ( 2 ) being dissolved by the chromate treatment.