Product for a welded construction made of AlMgMn alloy having improved mechanical strength

Abstract

Rolled or extruded products for welded constructions made of AlMgMn type aluminum alloy. These products contain, in % by weight, 3.0<Mg<5.0, 0.75<Mn<1.0, Fe<0.25, Si<0.25, 0.02<Zn<0.40, optionally one or more of the elements Cr, Cu, Ti, Zr such that Cr<0.25, Cu<0.20, Ti<0.20, Zr<0.20, other elements <0.05 each and <0.15 in total, wherein Mn+2Zn>0.75. In the welded state, these products have improved mechanical strength and resistance to fatigue without unfavorable consequences with regard to toughness and corrosion resistance, and are particularly suitable for naval construction, for industrial vehicles and for bicycle frames made of welded tubes.

What is claimed is:  
     
         1 . Aluminum alloy sheet for a welded construction, consisting essentially of, in % by weight: 
 3.0<Mg<5.0    0.5<Mn<1.0    0.02<Zn<0.40    Fe<0.25    Si<0.25    Cr<0.25    Cu<0.20    Ti<0.20    Zr<0.20    other elements <0.05 each and <0.15 total,    remainder Al,    wherein Mn+2Zn>0.75.    
     
     
         2 . Sheet according to  claim 1 , wherein Mn+2Zn>0.8.  
     
     
         3 . Sheet according to  claim 1 , wherein Cr<0.15.  
     
     
         4 . Sheet according to  claim 1 , wherein Mg>4.3.  
     
     
         5 . Sheet according to  claim 4 , wherein Mg>4.6.  
     
     
         6 . Sheet according to  claim 1 , wherein 0.10≦Zn<0.40.  
     
     
         7 . Sheet according to  claim 1 , wherein Mn>0.8.  
     
     
         8 . Sheet according to  claim 1 , wherein Fe<0.20.  
     
     
         9 . Sheet according to  claim 8 , wherein Fe<0.15.  
     
     
         10 . Sheet according to  claim 1 , wherein dispersoids are present in a volumetric fraction greater than 1.2%.  
     
     
         11 . Sheet according to  claim 1 , having a thickness >2.5 mm and obtained directly by hot rolling.  
     
     
         12 . Sheet according to  claim 1 , having, in an unwelded state, fatigue resistance, measured by plane bending wherein R=0.1 in the cross-longitudinal direction, higher than: 
 10 5  cycles, with a maximum stress >280 MPa;    10 6  cycles with a maximum stress >220 MPa;    10 7  cycles with a maximum stress >200 MPa.    
     
     
         13 . Sheet according to  claim 1 , having a fissure propagation rate ΔK, measured when R=0.1, higher than: 
 22 Mpa✓m when da/dn=5×10 −4  mm/cycle;  
 26 Mpa✓m when da/dn=10 −3  mm/cycle.  
 
     
     
         14 . Sheet according to  claim 1 , welded by fusion to form a welded zone, and having a hardness >80 Hv in the welded zone.  
     
     
         15 . Sheet according to  claim 1 , having a yield stress, measured on a standard DNV sample across an MIG butt welded joint, greater than 140 MPa.  
     
     
         16 . Sheet according to  claim 15 , having a yield stress, measured on a standard DNV sample across an MIG butt welded joint, greater than 150 MPa.