Al-Mg-Si ALUMININUM ALLOY EXTRUDED PRODUCT EXHIBITING EXCELLENT FATIGUE STRENGTH AND IMPACT FRACTURE RESISTANCE

Abstract

An aluminum alloy extruded product includes 0.3 to 0.8 mass % of Mg, 0.5 to 1.2 mass % of Si, 0.3 mass % or more of excess Si with respect to the Mg 2 Si stoichiometric composition, 0.05 to 0.4 mass % of Cu, 0.2 to 0.4 mass % of Mn, 0.1 to 0.3 mass % of Cr, 0.2 mass % or less of Fe, 0.2 mass % or less of Zr, and 0.005 to 0.1 mass % of Ti, with the balance being aluminum and unavoidable impurities, the aluminum alloy extruded product having a fatigue strength of 140 MPa or more, a fatigue ratio of 0.45 or more, and an interval between striations on a fatigue fracture surface of 5.0 μm or less.

1 . An aluminum alloy extruded product that exhibits excellent fatigue strength and impact fracture resistance, the aluminum alloy extruded product comprising 0.3 to 0.8 mass % of Mg, 0.5 to 1.2 mass % of Si, 0.3 mass % or more of excess Si with respect to the Mg 2 Si stoichiometric composition, 0.05 to 0.4 mass % of Cu, 0.2 to 0.4 mass % of Mn, 0.1 to 0.3 mass % of Cr, 0.2 mass % or less of Fe, 0.2 mass % or less of Zr, and 0.005 to 0.1 mass % of Ti, with the balance being aluminum and unavoidable impurities, the aluminum alloy extruded product having a fatigue strength of 140 MPa or more, a fatigue ratio of 0.45 or more, and an interval between striations on a fatigue fracture surface of 5.0 μm or less. 
   
   
       2 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product being produced by extruding an aluminum alloy ingot that has a maximum length of Al—Fe—Si crystallized products of 10 μm or less. 
   
   
       3 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product having an average grain size of 50 μm or less. 
   
   
       4 . The aluminum alloy extruded product as defined in  claim 1 , a forming load during extrusion of the aluminum alloy extruded product being 0.9 or less with respect to an alloy defined in JIS 6061. 
   
   
       5 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product that has been subjected to a solution treatment having a Lankford value of 0.7 or more. 
   
   
       6 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product that has been subjected to a solution treatment having a work hardening exponent of 0.23 or more. 
   
   
       7 . The aluminum alloy extruded product as defined in  claim 1 , the aluminum alloy extruded product that has been subjected to a solution treatment not producing cracks on its surface when subjected to a bending test that causes an outer surface elongation of 60% or more.