5000 series alloys with improved corrosion properties and methods for their manufacture and use

Abstract

The use of A1-5083 in a wide range of applications has been an industrial constant for many years. It possesses an excellent balance of properties, including high strength, good weldability, light weight and low cost. One of the commonly perceived drawbacks of the use of 5083 has been concern over susceptibility to stress corrosion cracking (SCC) and subsequent failure while in service. In the present invention, the susceptibility of high-magnesium Al—Mg alloys to SCC was evaluated with an eye toward altering SCC characteristics through compositional changes. These alloy composition changes are comprised of minor additions of Zn and Cu, in levels that are preferably low enough to minimize changes to the favorable bulk properties already inherent to A1-5083. Additionally, in accordance with the present invention, established industrial practices for material processing have been mimicked in order to evaluate the effects on inventive alloys in what would essentially be considered an as-supplied state. It has been shown that in tests on alloys subjected to an extreme degree of sensitization, and pulled to failure while immersed in a saltwater environment, compositions of the present invention provide a situation whereby potentially harmful grain boundary phase corrosion and failure is mitigated by the presence of various additions of copper.

We claim:  
     
         1 . An Al—Mg alloy wherein upon being subjected to a sensitization treatment a quaternary tau phase is formed at grain boundaries.  
     
     
         2 . An Al—Mg alloy according to  claim 1 , wherein said sensitization treatment is conducted between 80-200 degrees C.  
     
     
         3 . An Al—Mg alloy according to  claim 1 , comprising from 0.05-0.2% Cu.  
     
     
         4 . An Al—Mg alloy comprising: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 4.0-5.0%;  
 Mn 0.4-1.0%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         5 . An Al—Mg alloy according to  claim 4 , further comprising Ag 0.03-0.23%.  
     
     
         6 . An Al—Mg alloy according to  claim 4 , further comprising Cr 0-0.3%.  
     
     
         7 . An Al—Mg-alloy comprising: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 3.5-5.0%;  
 Mn 0.4-1.0%;  
 Incidental impurities; and  
 Al balance,  
 wherein upon being subjected to a sensitization treatment a quaternary Al—Mg—Zn—Cu phase is formed at grain boundaries.  
 
     
     
         8 . An Al—Mg alloy according to  claim 7 , wherein said sensitization treatment is conducted between 80 and 200° C.  
     
     
         9 . An Al—Mg alloy consisting essentially of: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 4.0-5.0%;  
 Mn 0.4-1.0%;  
 Ag 0.03-0.23%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         10 . An Al—Mg alloy consisting essentially of: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 4.0-5.0%;  
 Mn 0.4-1.0%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         11 . An Al—Mg alloy consisting essentially of: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 4.0-5.0%;  
 Mn 0.4-1.0%;  
 Cr 0-0.3%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         12 . An Al—Mg alloy comprising: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 3.9-5.0%;  
 Mn 0.4-1.0%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         13 . An Al—Mg alloy comprising: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 3.8-5.0%;  
 Mn 0.4-1.0%;  
 Cr 0-0.3%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         14 . An Al—Mg alloy comprising: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 3.5-6.5%;  
 Mn 0.4-1.0%;  
 Cr 0-0.3%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         15 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 1 .  
     
     
         16 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 4 .  
     
     
         17 . An Al—Mg based alloy having weldability, formability, corrosion resistance, and cost processing at a sheet or plate supplier approximating 5XXX alloys and further displaying a substantially reduced propensity to become corrosion-sensitive, even after being subjected to at least one sensitization treatment.  
     
     
         18 . An Al—Mg alloy according to  claim 17 , wherein said sensitization treatment is conducted between 80-200 degrees C.  
     
     
         19 . An Al—Mg alloy according to  claim 17 , comprising from 0.05-0.2% Cu.  
     
     
         20 . An Al—Mg alloy according to  claim 17  comprising: 
 Cu 0.05-0.2%;  
 Zn 0.3-0.6%;  
 Mg 4.0-5.0%;  
 Mn 0.4-1.0%;  
 Incidental impurities; and  
 Al balance.  
 
     
     
         21 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 6 .  
     
     
         22 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 7 .  
     
     
         23 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 8 .  
     
     
         24 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 9 .  
     
     
         25 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 10 .  
     
     
         26 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 11 .  
     
     
         27 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 12 .  
     
     
         28 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 13 .  
     
     
         29 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 14 .  
     
     
         30 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 17 .  
     
     
         31 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 18 .  
     
     
         32 . A marine product, railcar product, dump body, chemical tank cars, cryogenic application and/or auto body panel comprising an Al—Mg alloy according to  claim 19 .  
     
     
         33 . An Al—Mg alloy according to  claim 1 , wherein the tau phase formed has an average size from about 0.1 to about 1 μm and a mass loss according to ASTM G 67 of less than about 40 mg/cm 2 .  
     
     
         34 . An alloy according to  claim 33 , wherein said mass loss is less than about 27 mg/cm.  
     
     
         35 . An Al—Mg alloy after having been subjected to treatment at temperature of about 80-200 degrees C for sufficient time to establish a drop in ductility to failure from dry air to aqueous NaCl of less than about 10%.  
     
     
         36 . An alloy according to  claim 1 , wherein said sensitization treatment comprises a simulation of actual conditions in use.  
     
     
         37 . An alloy according to  claim 1 , wherein said sensitization treatment occurs during use.  
     
     
         38 . An Al—Mg alloy according to  claim 7 , comprising a tau phase having an average size from about 0.1 to about 1 μm and a mass loss according to ASTM G 67 of less than about 40 mg/cm 2 .  
     
     
         39 . An Al—Mg alloy according to  claim 38 , wherein said mass loss is less than about 27 mg/cm 2 .