Method Of Producing High-Intensity Aluminum Alloy Extruded Material Excellent In Resistance To Stress Corrosion Cracking And Aluminum Alloy Used Therefor

Abstract

A method of producing a high-intensity aluminum alloy extruded material excellent in resistance to stress corrosion cracking, the method comprising: preparing an Al—Zn—Mg-based aluminum alloy, subjecting the aluminum alloy to extrusion so that a temperature of an extruded material obtained immediately after the extrusion is 440° C. or more; allowing the extruded material to cool in an air at a cooling rate of less than 100° C./min until the temperature range of the extruded material reaches 300 to 400° C. from immediately after the extrusion for one minute to 3 minutes and 24 seconds; and then forced cooling the extruded material at a cooling rate of 100 to 2000° C./min until the temperature of the extruded material reaches 150° C. or less, followed by an aging treatment.

1 . A method of producing a high-intensity aluminum alloy extruded material excellent in resistance to stress corrosion cracking, the method comprising:
 preparing an aluminum alloy consisting of, by mass: Zn: 6.0 to 10.0%, Mg: 1.5 to 3.5%, Cu: 0.20 to 2.50%, Zr: 0.10 to 0.25%, Ti: 0.005 to 0.05%, Mn: 0.30 or less, Cr: 0.25% or less, a total of [Mn+Cr+Zr]: 0.10 to 0.50%, and a balance of Al and inevitable impurities, wherein an average crystalline particle diameter of the aluminum alloy after casting is 250 μm or less,   subjecting the aluminum alloy to extrusion so that a temperature of an extruded material obtained immediately after the extrusion is 440° C. or more;   allowing the extruded material to cool in an air at a cooling rate of less than 100° C./min until the temperature of the extruded material reaches 300 to 400° C. from immediately after the extrusion for one minute to 3 minutes and 24 seconds; and   then forced cooling the extruded material at a cooling rate of 100 to 2000° C./min until the temperature of the extruded material reaches 150° C. or less, followed by an aging treatment.   
     
     
         2 . The method of producing a high-intensity aluminum alloy extruded material excellent in resistance to stress corrosion cracking according to  claim 1 , wherein the aluminum alloy extruded material has a tensile strength of 500 MPa or more and a 0.2% proof stress of 470 MPa or more. 
     
     
         3 . The method of producing a high-intensity aluminum alloy extruded material excellent in resistance to stress corrosion cracking according to  claim 1 , wherein the aluminum alloy includes Zn: 8.0 to 10.0%, and the extruded material has a tensile strength of 600 MPa or more and a 0.2% proof stress of 600 MPa or more. 
     
     
         4 . An aluminum alloy comprising:
 by mass: Zn: 8.0 to 10.0%, Mg: 1.5 to 3.5%, Cu: 0.20 to 2.50%, Zr: 0.10 to 0.25%, Ti: 0.005 to 0.05%, Mn: 0.30 or less, Cr: 0.25% or less, a total of [Mn+Cr+Zr]: 0.10 to 0.50%, and a balance of Al and inevitable impurities,   wherein an average crystalline particle diameter of the aluminum alloy after casting is 250 μm or less.