6000-series aluminium extruded material superior in paint-baking hardenability and method for manufacturing the same

Abstract

This invention relates to a 6000-series aluminum extruded material containing magnesium (0.3% to 0.7% by mass), silicon (0.7% to 1.5% by mass), copper (0.35% or less by mass), iron (0.35% or less by mass), titanium (0.005% to 0.1% by mass), manganese (0.05% to 0.30% by mass), chrome (0.10% or less by mass), and zirconium (0.10% or less by mass) (provided that at least one transition element selected from the group consisting of manganese, chromium, and zirconium is contained in a total amount representing 0.05% to 0.40% by mass), with the balance comprising aluminum with inevitable impurities, such aluminium extruded material having a predetermined yield strength of 180 MPa or more with an increase of 60 MPa as a result of a thermal history corresponding to paint baking. Such 6000-series aluminium extruded profile is superior in paint-baking hardenability and thus the yield strength thereof can be secured to a level applicable to structural members of automobiles and the like with the use of a thermal history corresponding to paint baking.

1 . A 6000-series aluminum extruded material containing magnesium (0.3% to 0.7% by mass), silicon (0.7% to 1.5% by mass), copper (0.35% or less by mass), iron (0.35% or less by mass), titanium (0.005% to 0.1% by mass), manganese (0.05% to 0.30% by mass), chrome (0.10% or less by mass), and zirconium (0.10% or less by mass) (provided that at least one transition element selected from the group consisting of manganese, chromium, and zirconium is contained in a total amount representing 0.05% to 0.40% by mass), with the balance comprising aluminum with inevitable impurities, such aluminium extruded material having a predetermined yield strength of 180 MPa or more with an increase of 60 MPa as a result of a thermal history corresponding to paint baking. 
   
   
       2 . The 6000-series aluminum extruded material according to  claim 1 , which has been retained at 90±50° C. for 1 to 24 hours within 72 hours after extrusion molding. 
   
   
       3 . The 6000-series aluminum extruded material according to  claim 1 , which is obtained by setting the billet temperature at 500° C. or more and the cooling rate at not less than 70° C./min for 4 minutes immediately after extrusion during manufacturing of the extruded material. 
   
   
       4 . A method for manufacturing a 6000-series aluminium extruded material having a predetermined yield strength of 180 MPa or more with an increase of 60 MPa as a result of a thermal history corresponding to paint baking, comprising carrying out extrusion molding of an aluminium alloy ingot containing magnesium (0.3% to 0.7% by mass), silicon (0.7% to 1.5% by mass), copper (0.35% or less by mass), iron (0.35% or less by mass), titanium (0.005% to 0.1% by mass), manganese (0.05% to 0.30% by mass), chrome (0.10% or less by mass), and zirconium (0.10% or less by mass) (provided that at least one transition element selected from the group consisting of manganese, chromium, and zirconium is contained in a total amount representing 0.05% to 0.40% by mass), with the balance comprising aluminum with inevitable impurities. 
   
   
       5 . The method for manufacturing a 6000-series aluminium extruded material according to  claim 4 , wherein the extruded material is retained at 90±50° C. for to 24 hours immediately after the extrusion molding. 
   
   
       6 . The method for manufacturing a 6000-series aluminium extruded material according to  claim 4  or  5 , comprising setting the billet temperature at 500° C. or more and the cooling rate at not less than 70° C./min for 4 minutes immediately after extrusion during manufacturing of the extruded material.