Method For Producing High-Strength Aluminum Alloy Extruded Product

Abstract

A method for producing a high-strength aluminum alloy extruded product includes casting a billet using an aluminum alloy containing, by mass %, 6.0 to 8.0% of Zn, 1.0 to 3.5% of Mg, 0.2 to 1.5% of Cu, 0.10 to 0.25% of Zr, 0.005 to 0.05% of Ti, and 0.5% or less of Mn, [Mn+Zr] being 0.10 to 0.60%, with the balance being Al and unavoidable impurities, homogenizing the billet and then extruding the homogenized billet without being cooled, cooling an extruded product immediately after the extrusion at an average rate of 70 to 500° C./min, and then performing artificial aging.

What is claimed is: 
     
         1 . A method for producing a high-strength aluminum alloy extruded product, comprising:
 casting a billet using an aluminum alloy containing, by mass %, 6.0 to 8.0% of Zn, 1.0 to 3.5% of Mg, 0.2 to 1.5% of Cu, 0.10 to 0.25% of Zr, 0.005 to 0.05% of Ti, and 0.5% or less of Mn, [Mn+Zr] being 0.10 to 0.60%, with the balance being Al and unavoidable impurities;   homogenizing the billet and then extruding the homogenized billet without being cooled;   cooling an extruded product immediately after the extrusion at an average rate of 70 to 500° C./min; and then   performing artificial aging.   
     
     
         2 . The method for producing a high-strength aluminum alloy extruded product according to  claim 1 , wherein in casting the billet, a casting rate is 50 mm/min or more and an average crystal grain size of a cast structure is 300 μm or less. 
     
     
         3 . The method for producing a high-strength aluminum alloy extruded product according to  claim 2 , wherein the artificial aging is a two-stage heat treatment with a total heat treatment time of 20 hours or less, the two-stage heat treatment including a first stage performed at 80 to 130° C. for 7 hours or less and a second stage performed at 130 to 160° C. for 13 hours or less. 
     
     
         4 . The method for producing a high-strength aluminum alloy extruded product according to  claim 3 , wherein the high-strength aluminum alloy has a tensile strength of 400 MPa or more and a 0.2% proof stress of 380 MPa or more.