Method for surface treatment of sheets and strips of aluminium alloy

Abstract

A method for surface treatment of sheets and strips of aluminum alloy to form a chemically altered layer. The sheet or strip is the product of a manufacturing process including a thermal treatment step followed by cooling in a liquid in which a chemical conversion is carried out using the cooling liquid. The cooling liquid preferably contains between 1 and 10% by weight of at least one salt of one at least of the metals Si, Ti, Zr, Ce, Mn, Mo and V. The invention is particularly applicable to sheets and strips which need a controlled oxide surface for the production of chassis components for the automobile industry for spot gluing or welding.

1 . Surface treatment process for an aluminum alloy sheet or strip to form a chemical conversion coating, the sheet or strip being derived from a manufacturing procedure comprising a heat treatment followed by cooling in a liquid, in which chemical conversion is done using the cooling liquid.  
     
     
         2 . Process according to  claim 1 , wherein the aluminum alloy is in the 5000 series or 6000 series.  
     
     
         3 . Process according to  claim 1 , wherein the conversion coating has a thickness between 5 and 50 nm.  
     
     
         4 . Process according to  claim 1 , wherein the cooling liquid contains between 1 and 10% by weight of at least one salt of at least one metal selected from the group consisting of Si, Ti, Zr, Ce, Mn, Mo and V.  
     
     
         5 . Process according to  claim 1 , wherein the cooling liquid has a pH between 3 and 11.  
     
     
         6 . Process according to  claim 1 , wherein the chemical conversion done using the cooling liquid does not require any prior or post surface treatment.