High-strength aluminum alloy product and method of producing the same

Abstract

A heat-treated high-strength Al—Cu—Mg—Si aluminum alloy product exhibits excellent extrudability and high strength. The high-strength Al—Cu—Mg—Si aluminum alloy product obtained by extrusion is characterized in that the microstructure of the entire surface of the cross section of the aluminum alloy product is formed of recrystallized grains, the grains have an average aspect ratio (L/t) of 5.0 or less (wherein L is the average size of the grains in the extrusion direction, and t is the average thickness of the grains), and the orientation density of the grains in the microstructure, for which the normal direction to the {001} plane is parallel to the extrusion direction in comparison with the grains orientated to random orientations, is 50 or less. The high-strength Al—Cu—Mg—Si aluminum alloy product obtained by extrusion and cold working is characterized in that rod-shaped precipitates are arranged in the grains of the matrix in the <100> direction, the precipitates have an average length of 10 to 70 nm and a maximum length of 120 nm or less, and the number density of the precipitates in the [001] direction measured from the (001) plane is 500 or more per square micrometer.

1 . A high-strength Al—Cu—Mg—Si aluminum alloy product obtained by extrusion, the microstructure of the entire cross section of the aluminum alloy product being formed of recrystallized grains, the grains having an average aspect ratio (L/t) of 5.0 or less (wherein L is the average size of the grains in the extrusion direction, and t is the average thickness of the grains), and the orientation density of the grains in the microstructure, for which the normal direction to the {001} plane is parallel to the extrusion direction in comparison with the grains oriented to random orientations, is 50 or less. 
   
   
       2 . The aluminum alloy product according to  claim 1 , comprising 0.6 to 3.0% (mass %, hereinafter the same) of Cu, 0.4 to 1.6% of Mg, and 0.2 to 1.4% of Si, with the balance being Al and unavoidable impurities. 
   
   
       3 . The aluminum alloy product according to  claim 2 , further comprising at least one of 0.50% or less (excluding 0%, hereinafter the same) of Mn, 0.40% or less of Cr, 0.20% or less of Zr, and 0.20% or less of V. 
   
   
       4 . The aluminum alloy product according to  claim 2 , further comprising at least one of 0.15% or less of Ti and 50 ppm or less of B. 
   
   
       5 . The aluminum alloy product according to  claim 1 , wherein the ratio (D/T) of the diameter D of a billet of the aluminum alloy product before extrusion to the minimum thickness T of the cross section of the extruded product is 200 or less. 
   
   
       6 . The aluminum alloy product according to  claim 1 , the aluminum alloy product being obtained by extrusion at an extrusion ratio of 20 or more. 
   
   
       7 . A high-strength Al—Cu—Mg—Si aluminum alloy product obtained by extrusion and cold working, rod-shaped precipitates being arranged in the grains of the matrix in the <100> direction, the precipitates having an average length of 10 to 70 nm and a maximum length of 120 nm or less, and the number density of the precipitates in the [001] direction measured from the (001) plane being 500 or more per square micrometer. 
   
   
       8 . The aluminum alloy product according to  claim 7 , comprising 1.0 to 3.0% of Cu, 0.4 to 1.8% of Mg, and 0.2 to 1.6% of Si, with the balance being Al and unavoidable impurities. 
   
   
       9 . The aluminum alloy product according to  claim 8 , further comprising at least one of 0.30% or less of Mn, 0.40% or less of Cr, 0.25% or less of Zr, and 0.10% or less of V. 
   
   
       10 . The aluminum alloy product according to  claim 8 , further comprising at least one of 0.15% or less of Ti and 50 ppm or less of B. 
   
   
       11 . The aluminum alloy product according to  claim 7 , wherein the matrix has a structure formed of equiaxial recrystallized grains, and has an average aspect ratio (L/ST) of the average size L of the grains in the extrusion direction to the average size ST of the grains in the thickness direction of 1.5 to 4.0. 
   
   
       12 . The aluminum alloy product according to  claim 7 , the aluminum alloy product having a ultimate tensile strength of 450 MPa or more, a proof stress of 400 MPa or more, and an elongation of 7% or more. 
   
   
       13 . A method of producing the aluminum alloy product having a composition according to  claim 8  in a hollow shape to obtain a hollow extruded product, subjecting the hollow extruded product to a solution heat treatment and quenching, cold-working the hollow extruded product so that the cross-sectional area and the external profile of the hollow extruded product are reduced, and aging the resulting product. 
   
   
       14 . The method according to  claim 13 , wherein the hollow extruded product is cold-worked by drawing the hollow extruded product at a rate of reduction in cross-sectional area of 10 to 50% and a rate of reduction in external profile of 7 to 35%. 
   
   
       15 . The method according to  claim 13 , further comprising press-quenching the hollow extruded product after the hot extrusion.