7000-series aluminum alloy extruded product and method of producing the same

Abstract

A method of producing an aluminum alloy extruded product comprising: casting a billet using a 7000-series aluminum alloy having Mg of 0.95 to 1.95 mass %, Zn of 5.10 to 7.90 mass %, an excess mg or Zn content relative to a stoichiometric composition shown by MgZn2 of less than 0.5 mass %; an A=Zn−5.36×Mg (mass %) of −2.64 to 0.50; and at least one of Mn, Cr and Zr with a total content thereof being less than 0.25 mass %; homogenizing the billet at 450 to 550° C.; preheating the homogenized product at 480 to 540° C.; extruding the preheated product with a die heated at 440 to 500° C.; and subjecting the extruded product to press quenching at an air cooling rate of 29° C./min or more, wherein a proof stress increase due to natural aging is 15 Mpa or less and a hardness HV increase due to natural aging is seven or less.

1 . A method of producing an aluminum alloy extruded product, the method comprising:
 casting a billet using a 7000-series aluminum alloy having an Mg content of 0.95 to 1.95 mass %, a Zn content of 5.10 to 7.90 mass %, an excess mg content or an excess Zn content with respect to a stoichiometric composition shown by MgZn2 of less than 0.5 mass %; a value A indicated by a relational expression A=Zn−5.36×Mg (mass %) of −2.64 to 0.50; and at least one of Mn, Cr, and Zr, a total content of Mn, Cr, and Zr being less than 0.25 mass %;   homogenizing the billet at 450 to 550° C.;   preheating the homogenized product at 480 to 540° C.;   extruding the preheated product with an extrusion die that is heated at 440 to 500° C.; and   subjecting the extruded product to press quenching at an air cooling rate of 29° C./min or more,   wherein an increase in proof stress due to natural aging is 15 Mpa or less and an increase in hardness HV due to natural aging is seven or less, when comparing the proof stress and the hardness of the aluminum alloy extruded product obtained by subjecting the aluminum alloy to natural aging at 50° C. or less for one week after extrusion and then subjecting the resulting product to artificial aging with the proof stress of the aluminum alloy extruded product obtained by subjecting the aluminum alloy to artificial aging immediately after extrusion.   
     
     
         2 . The method as defined in  claim 1 , wherein the extruded product immediately after extrusion is 580° C. or less.