Al-Mg-Si Alloy Exhibiting Superior Combination of Strength and Energy Absorption

Abstract

The present invention relates to an aluminum 6XXX (Al—Mg—Si) alloy extrusion component exhibiting a superior combination of strength and energy absorption for crash management applications in automotive markets and for other applications where energy absorption is a critical property. These components provide yield strengths greater than 260 MPa, and preferably greater than 280 MPa, while simultaneously providing energy absorption per unit cross-sectional area of greater than 20 kJ/mm 2 using the defined crush testing parameters in the present specification.

1 . An energy absorption extrusion component produced from an alloy composition comprising, in weight percent, Si: 0.50-0.80; Fe: <0.40; Cu: 0.15-0.35; Mn: 0.20-0.50; Mg: 0.50-0.80; Cr: 0.10-0.25; Zn: <0.20; with other elements being considered incidental elements and consisting of less than 0.05 individually and 0.15 in total with the balance being aluminum 
     
     
         2 . The component of  claim 1  wherein said extrusion component has a specific energy absorption of greater than 22 kJ/mm 2  and a yield strength of greater than 260 MPa while providing no fragmentation or surface cracks greater than 10 mm during defined crush testing wherein a 300 mm long sample is crushed in the longitudinal direction to 100 mm at a rate of 100 mm/minute. 
     
     
         3 . The component of  claim 1 , wherein said extrusion component has a yield strength greater than 280 MPa. 
     
     
         4 . The component of  claim 1  wherein said extrusion component has a specific energy absorption of greater than 22 kJ/mm 2  and a yield strength greater than 280 MPa with no fragmentation or surface crack greater than 20 mm during defined crush testing wherein a 300 mm long sample is crushed in the longitudinal direction to 100 mm at a rate of 100 mm/minute. 
     
     
         5 . The component of  claim 1  wherein said extrusion component has a specific energy absorption of greater than 22 kJ/mm 2  and a yield strength greater than 300 MPa with no fragmentation or surface crack greater than 30 mm during defined crush testing wherein a 300 mm long sample is crushed in the longitudinal direction to 100 mm at a rate of 100 mm/minute. 
     
     
         6 . The component of  claim 1  wherein said alloy composition further comprises Sn that is intentionally added at levels of 0.02-0.10% by weight. 
     
     
         7 . The component of  claim 1  wherein said alloy composition further comprises Sr that is intentionally added at levels up to 0.30% by weight. 
     
     
         8 . The component of  claim 1  wherein said alloy composition further comprises V that is not intentionally added. 
     
     
         9 . The component of  claim 1  wherein said alloy composition further comprises V ≤0.04% by weight. 
     
     
         10 . The component of  claim 1  used as an automotive crush can, front rail, rear rail, upper rail, rocker, header, A-pillar, or roof rail. 
     
     
         11 . A method for making the extrusion component of  claim 1  comprising,
 i) homogenizing a billet including said alloy composition at a billet temperature between 527-566° C., 
 ii) followed by fan cooling, 
 iii) followed by either a) extruding with a billet temperature between 455° C. to 510° C. or b) heating to a billet temperature of 491° C.-535° C., then water quenching to a billet temperature of 388° C.-496° C., and then extruding, 
 iv) followed by cold water quenching; stretching; and artificial aging wherein the extrusion component has a specific energy absorption of greater than 22 kJ/mm 2  and a yield strength of greater than 260 MPa while providing no fragmentation or surface cracks greater than 10 mm during defined crush testing wherein a 300 mm long sample is crushed in the longitudinal direction to 100 mm at a rate of 100 mm/minute. 
 
     
     
         12 . The method of  claim 11 , wherein the billet is initially heated to 491° C.-535° C., then water quenched to a temperature of 388° C.-496° C. prior to extruding. 
     
     
         13 . The method of  claim 11 , wherein the billet is extruding with a billet temperature between 455° C. to 510° C. after fan cooling 
     
     
         14 . The method of  claim 11  wherein said extrusion component has a coarse surface grain depth that is controlled to less than 0.5 mm in depth from the surface. 
     
     
         15 . The method of  claim 11  wherein the artificial aging is conducted using a two-step cycle with a second aging step being hotter than a first aging step and either aging steps ranging between 100-204° C. 
     
     
         16 . The method of  claim 15 , wherein the two-step age cycle involves a first aging step from 100-177° C. and a second aging step from 172-204° C. 
     
     
         17 . The method of  claim 11  wherein the artificial aging is conducted at a billet temperature between 174-191° C. for 5-10 hours. 
     
     
         18 . The method of  claim 11  wherein said component is provided in an unaged (T4) condition with artificial aging conducted post forming. 
     
     
         19 . The method of  claim 11  wherein said component is provided in an under-aged condition with the remaining peak age strengthening accomplished during subsequent thermal operations.