High-strength aluminum alloy and manufacturing method thereof

Abstract

An aluminum alloy suitable for anodizing contains, in mass percent, Zn: 5.0% or more and 7.0% or less, Mg: more than 2.2% and 3.0% or less, Cu: 0.01% or more and 0.10% or less, Zr: 0.10% or less, Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, and Ti: 0.001% or more and 0.05% or less, the remainder being composed of Al and unavoidable impurities. The aluminum alloy has a Zn/Mg ratio of 1.7 or more and 3.1 or less, a proof stress of 350 MPa or more and a metallographic structure composed of a recrystallized structure.

1 .- 5 . (canceled) 
     
     
         6 . An aluminum alloy, comprising in mass percent:
 Zn: 5.0% or more and 7.0% or less,   Mg: more than 2.2% and 3.0% or less,   Cu: 0.01% or more and 0.10% or less,   Zr: 0.10% or less,   Cr: 0.02% or less,   Fe: 0.30% or less,   Si: 0.30% or less,   Mn: 0.02% or less, and   Ti: 0.001% or more and 0.05% or less,   the remainder being composed of Al and unavoidable impurities,   wherein the aluminum alloy has:
 a Zn/Mg ratio of 1.7 or more and 3.1 or less, 
 a proof stress of 350 MPa or more, and 
 a metallographic structure composed of a recrystallized structure. 
   
     
     
         7 . The aluminum alloy according to  claim 6 , wherein:
 the recrystallized structure includes crystal grains having an average grain diameter of 500 μm or less, and   a crystal grain length in a direction parallel to a hot working direction is 0.5 to 4 times as long as a crystal grain length in a direction perpendicular to the hot working direction.   
     
     
         8 . The aluminum alloy according to  claim 7 , wherein Zn is more than 5.2% and 6.8% or less. 
     
     
         9 . The aluminum alloy according to  claim 8 , wherein the aluminum alloy has an anodized surface that has a b* value of 0 or more and 0.8 or less. 
     
     
         10 . The aluminum alloy according to  claim 9 , wherein the recrystallized structure is a granular recrystallized structure. 
     
     
         11 . The aluminum alloy according to  claim 6 , wherein Zn is more than 5.2% and 6.8% or less. 
     
     
         12 . The aluminum alloy according to  claim 6 , wherein the aluminum alloy has an anodized surface that has a b* value of 0 or more and 0.8 or less. 
     
     
         13 . The aluminum alloy according to  claim 6 , wherein the recrystallized structure is a granular recrystallized structure. 
     
     
         14 . A process for producing a wrought aluminum alloy material, which comprises:
 preparing an ingot having a chemical composition comprising, in mass percent, Zn: 5.0% or more and 7.0% or less, Mg: more than 2.2% and 3.0% or less, Cu: 0.01% or more and 0.10% or less, Zr: 0.10% or less, Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, and Ti: 0.001% or more and 0.05% or less, the remainder being composed of Al and unavoidable impurities and a Zn/Mg ratio being 1.7 or more and 3.1 or less;   performing a homogenization treatment that heats the ingot at a temperature of higher than 540° C. and 580° C. or lower for 1 hour to 24 hours;   subsequently, forming a wrought material by performing hot working on the ingot in a state where the temperature of the ingot at the beginning of the working is 440° C. to 560° C.;   while the wrought material is still at 400° C. or higher, starting to cool it and subsequently performing a quenching treatment such that, while the wrought material is cooling down from 400° C. to 150° C., the average cooling rate is 1° C./s or more and 300° C./s or less;   cooling the temperature of the wrought material to room temperature by said quenching treatment or by an additional cooling treatment; and   thereafter, performing an artificial aging treatment on the wrought material.   
     
     
         15 . The process according to  claim 14 , wherein the artificial aging treatment comprises performing a first artificial aging treatment at a temperature of 80° C. to 120° C. for 1 hour to 5 hours, and continuously after the first artificial aging treatment, performing a second artificial aging treatment that heats the wrought material at a temperature of 145° C. to 200° C. for 2 hours to 15 hours. 
     
     
         16 . The process according to  claim 14 , wherein the artificial aging treatment comprises heating the wrought material at a temperature of 145° C. to 170° C. for 1 hour to 24 hours. 
     
     
         17 . The process according to  claim 14 , wherein the hot working involves extrusion or rolling. 
     
     
         18 . The process according to  claim 14 , wherein during the quenching step, the average cooling rate is 3° C./s or more and 300° C./s or less 
     
     
         19 . The process according to  claim 14 , wherein the second artificial aging treatment is performed at a temperature of 170° C. to 200° C. 
     
     
         20 . The process according to  claim 14 , further comprising anodizing the wrought material after the artificial aging treatment. 
     
     
         21 . The process according to  claim 14 , wherein:
 the homogenization treatment is performed at 550° C. for 6 hours,   the hot working comprises hot extruding the ingot while the temperature of the ingot is at 520° C.,   the quenching treatment is initiated while the temperature of the wrought material is at 505° C. and the average cooling rate of the quenching treatment is 60° C./sec, thereafter the wrought material is subjected to room temperature aging for 24 hours,   the first artificial aging treatment involves heating the wrought material at 100° C. for 4 hours, and   the second artificial aging treatment involves heating the wrought material at 160° C. for 8 hours.   
     
     
         22 . The process according to  claim 21 , further comprising anodizing the wrought material after the second artificial aging treatment. 
     
     
         23 . A process for producing the aluminum alloy of  claim 6 , comprising:
 homogenizing an ingot having the elemental composition recited in  claim 6  at a temperature of higher than 540° C. and 580° C. or lower for at least 1 hour;   hot working on the homogenized ingot while the temperature of the ingot at the beginning of the hot working is 440° C. to 560° C., thereby forming a wrought material,   while the wrought material is still at 400° C. or higher, starting to cool it and subsequently performing a quenching treatment such that, while the wrought material is cooling down from 400° C. to 150° C., the average cooling rate is 1° C./s or more and 300° C./s or less;   cooling the temperature of the wrought material to room temperature by said quenching treatment or by an additional cooling treatment; and   thereafter, performing an artificial aging treatment on the wrought material.   
     
     
         24 . The process according to  claim 23 , wherein the artificial aging treatment comprises performing a first artificial aging treatment at a temperature of 80° C. to 120° C. for 1 hour to 5 hours, and continuously after the first artificial aging treatment, performing a second artificial aging treatment that heats the wrought material at a temperature of 145° C. to 200° C. for 2 hours to 15 hours. 
     
     
         25 . The process according to  claim 23 , wherein the artificial aging treatment comprises heating the wrought material at a temperature of 145° C. to 170° C. for 1 hour to 24 hours.