Method for Producing Aluminum Alloy Extrusion

Abstract

A method for producing an aluminum alloy extrusion includes: conducting extrusion processing using a casted billet of an aluminum alloy containing 6.0 to 7.0% by mass of Zn, 1.5 to 2.0% by mass of Mg, 0.20 to 1.50% by mass of Cu, 0.10 to 0.25% by mass of Zr, 0.005 to 0.05% by mass of Ti, 0.15 to 0.35% by mass of Mn, 0.25% by mass or less of Sr, content of Mn and Zr and Sr being 0.10 to 0.50% by mass, with the balance being Al and inevitable impurities to obtain an aluminum alloy extrusion; cooling the extrusion to 100° C. or less at a cooling rate of 50 to 750° C./min immediately after the extrusion processing; and then conducting an aging treatment which is performed in one-stage or two-stage and a heat treatment which is performed at higher temperature for a shorter time than the aging treatment.

What is claimed is: 
     
         1 . A method for producing an aluminum alloy extrusion includes:
 conducting extrusion processing using a casted billet of an aluminum alloy containing 6.0 to 7.0% by mass of Zn, 1.5 to 2.0% by mass of Mg, 0.20 to 1.50% by mass of Cu, 0.10 to 0.25% by mass of Zr, 0.005 to 0.05% by mass of Ti, 0.15 to 0.35% by mass of Mn, 0.25% by mass or less of Sr, content of Mn and Zr and Sr being 0.10 to 0.50% by mass, with the balance being Al and inevitable impurities to obtain an aluminum alloy extrusion; cooling the extrusion to 100° C. or less at a cooling rate of 50 to 750° C./min immediately after the extrusion processing; and   then conducting an aging treatment which is performed in one-stage or two-stage and a heat treatment which is performed at higher temperature for a shorter time than the aging treatment.   
     
     
         2 . The method as defined in  claim 1 ,
 wherein the casted billet is subjected to homogenizing treatment at 480 to 520° C. subsequently to casting and then cooled at a cooling rate of 50° C./hr or more so that an average crystal grain size is 250 μm or less.   
     
     
         3 . The method as defined in  claim 2 ,
 wherein the aluminum alloy extrusion has a tensile strength of 460 MPa or more and a proof stress of 430 MPa or more.