Shock absorbing material

Abstract

A shock absorbing material comprising an Al—Mg—Si series aluminum alloy having high strength and showing excellent energy absorbing property when compressed in the axial direction of extrusion is obtained. The shock absorbing material of the invention has a hollow cross section, mainly comprises a fibrous structure and can be manufactured by press quenching just after extrusion followed by aging. In the press quenching, press quenching under air-cooling advantageous in view of the dimensional accuracy or the cost can be adopted. Further, the shock absorbing material of the invention has excellent cracking resistance to a compressive load in the lateral direction as well as in the axial direction. The shock absorbing material of the invention is suitable as side members or bumper stays in the frame structures of automobiles.

What is claimed is:  
     
         1 . A shock absorbing material comprising an Al—Mg—Si series aluminum alloy containing: 
 from 0.30 to 0.70wt % of Mg;  
 from 0.10 to 0.50wt % of Si in excess of a balanced composition for Mg 2 Si; and  
 from 0.10 to 0.40wt % of one or more of Mn, Cr and Zr in total, wherein said shock absorbing material is of a hollow cross section, comprises a microstructure having a fibrous and has an yield stress of 210 MPa or more.  
 
     
     
         2 . The shock absorbing material as defined in  claim 1 , wherein said microstructure further comprises surface recrystallization layer with the thickness being 10% or less and the thickness of said fibrous structure is 50% or more for the entire.  
     
     
         3 . The shock absorbing material as defined in  claim 1 , wherein the total amount of Si is from 0.50 to 0.70wt %.  
     
     
         4 . The shock absorbing material as defined in  claim 1 , further containing from 0.10 to 0.40% of Cu.  
     
     
         5 . The shock absorbing material as defined in  claim 1 , further containing from 0.005 to 0.2% of Ti.  
     
     
         6 . The shock absorbing material as defined in  claim 1 , being obtainable from an aluminum alloy extrusion material and by conducting press quenching under air cooling just after extrusion and then conducting aging.  
     
     
         7 . The shock absorbing material as defined in  claim 1 , being obtainable from an aluminum alloy extrusion material and by conducting press quenching at a cooling rate of 100 to 300° C./min just after extrusion and then applying aging.  
     
     
         8 . A shock absorbing material comprising an Al—Mg—Si series aluminum alloy containing: 
 from 0.20 to 1.1wt % of Mg; and  
 from 0.20 to 1.2wt % of Si,  
 wherein said shock absorbing material is of a hollow cross section and comprises a microstructure having the thickness of a surface recrystallization layer of 1 to 50% for the entire thickness with the balance of a fibrous structure, having a grain size in the direction of the thickness of the surface recrystallization layer of 200 μm or less, and having an yield stress of 200 MPa or more.  
 
     
     
         9 . The shock absorbing material as defined in  claim 8 , containing from 0.40 to 0.80wt % of Mg and from 0.50 to 1.0wt % of Si.  
     
     
         10 . The shock absorbing material as defined in  claim 8 , further containing one or more of Mn, Cr and Zr within a range from 0.05 to 0.40% of Mn, from 0.05 to 0.20% of Cr and from 0.05 to 0.20% of Zr.  
     
     
         11 . The shock absorbing material as defined in  claim 8 , further containing from 0.05 to 0.7% of Cu.  
     
     
         12 . The shock absorbing material as defined in  claim 8 , further containing from 0.005 to 0.2% of Ti.  
     
     
         13 . A shock absorbing material comprising an Al—Mg—Si series aluminum alloy containing: 
 from 0.20 to 1.1wt % of Mg; and  
 from 0.20 to 1.2wt % of Si,  
 wherein said absorbing material is of a hollow cross section and has a thickness reduction ratio of 25% or more at the ruptured cross section when applying a tensile test.  
 
     
     
         14 . The shock absorbing material as defined in  claim 13 , containing from 0.40 to 0.80wt % of Mg and from 0.50 to 1.1wt % of Si.  
     
     
         15 . The shock absorbing material as defined in  claim 13 , further containing one or more of Mn, Cr and Zr within a range from 0.05 to 0.40% of Mn, from 0.05 to 0.20% of Cr and from 0.05 to 0.20% of Zr.  
     
     
         16 . The shock absorbing material as defined in  claim 13 , further containing from 0.05 to 0.7% of Cu.  
     
     
         17 . The shock absorbing material as defined in  claim 13 , further containing from 0.005 to 0.2% of Ti.  
     
     
         18 . The shock absorbing material as defined in  claim 13 , being obtainable by press quenching just after extrusion and then applying aging treatment.