Aluminum alloy extruded product exhibiting excellent impact cracking resistance and impact absorber

Abstract

An aluminum alloy extruded product that exhibits excellent impact cracking resistance is formed of an aluminum alloy that includes 0.50 to 0.75 mass % of Mg, 4.5 to 6.5 mass % of Zn, 0.10 to 0.20 mass % of Cu, 0.17 to 0.23 mass % of Zr, 0.005 to 0.05 mass % of Ti, 0.05 mass % or less of Mn, 0.03 mass % or less of Cr, 0.20 mass % or less of Fe, and 0.10 mass % or less of Si, with the balance being Al and unavoidable impurities.

1 . An aluminum alloy extruded product that exhibits excellent impact cracking resistance, the aluminum alloy extruded product being formed of an aluminum alloy that comprises 0.50 to 0.75 mass % of Mg, 4.5 to 6.5 mass % of Zn, 0.10 to 0.20 mass % of Cu, 0.17 to 0.23 mass % of Zr, 0.005 to 0.05 mass % of Ti, 0.05 mass % or less of Mn, 0.03 mass % or less of Cr, 0.20 mass % or less of Fe, and 0.10 mass % or less of Si, with the balance being Al and unavoidable impurities. 
   
   
       2 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy having an Mn content of 0.01 mass % or less and a Cr content of 0.01 mass % or less. 
   
   
       3 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product having been subjected to forced air cooling at a cooling rate of 30° C./min or more immediately after extrusion until a material surface temperature is reduced to 100° C. or less, and then subjected to artificial aging. 
   
   
       4 . The aluminum alloy extruded product as defined in  claim 3 , the aluminum alloy extruded product having been subjected to artificial aging so that the aluminum alloy extruded product has a proof stress approximately equal to a peak strength that is equal to or larger than a value 0.9 times a maximum strength of the aluminum alloy extruded product. 
   
   
       5 . The aluminum alloy extruded product as defined in  claim 4 , the aluminum alloy extruded product having a precipitate-free zone (PFZ) of 100 nm or less. 
   
   
       6 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product having a hollow cross section and exhibiting excellent impact cracking resistance during axial collapse along an extrusion direction. 
   
   
       7 . An impact absorber obtained by welding an extruded product produced by extruding an aluminum alloy to another member, allowing the resulting product to stand at room temperature for one or more days, and subjecting the resulting product to artificial aging, the aluminum alloy comprising 0.50 to 0.75 mass % of Mg, 4.5 to 6.5 mass % of Zn, 0.10 to 0.20 mass % of Cu, 0.17 to 0.23 mass % of Zr, 0.005 to 0.05 mass % of Ti, 0.05 mass % or less of Mn, 0.03 mass % or less of Cr, 0.20 mass % or less of Fe, and 0.10 mass % or less of Si, with the balance being Al and unavoidable impurities.