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  Aluminum alloyAluminum alloy description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070297936, Aluminum alloy. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]1. Field of the Invention [0002]The present invention relates to an aluminum alloy with magnesium, scandium and zirconium contents in the range of 2.2-3.0 wt. %, 0.1-0.97 wt. % and 0.14-0.9 wt. %, respectively, in the form of extruded products suitable for applications that require a combination of strength and corrosion resistance. More specifically the alloy is suitable for applications requiring service within seawater or in marine or industrial environments. Further the invention relates to a method of manufacturing the alloy. [0003]2. Description of the Related Art [0004]Several efforts have been made in the past to lower the density of Al--Mg (5XXX series) alloys to the level of Al--Zn--Mg--Cu (Al 7075) alloys and elevate the strength to the levels of precipitation hardening alloys. Although Al--Mg alloys with substantially high magnesium content (10 wt. %) approach the strength of precipitation-hardened alloys, such alloys create enormous processing difficulties and exhibit stress corrosion cracking. Since, for practical purposes, the amount of magnesium that can be retained in solid solution at room temperature is around 3 wt. %, any higher amount results in the precipitation of Al--Mg intermetallics at the alloy grain boundaries. This makes the alloy susceptible to corrosion damage. Therefore, the need exists for aluminum alloys with magnesium content lower than 3 wt. % to counter corrosion attack. [0005]Aluminum alloy AA5052 is such an alloy, which has good corrosion resistance to seawater and marine and industrial atmosphere. However, due to relatively lower magnesium content, it exhibits strength of only medium high level. An increase in strength levels of AA5052 without an appreciable decrease in its corrosion resistance will widen its field of applications and allow more flexibility in the use of material dimensions for various components. [0006]Aluminum-magnesium alloys are lower in density compared to 2000 and 7000 series alloys and are weldable by conventional fusion techniques. To increase the strength of aluminum-magnesium alloys, small amounts of scandium are added to the alloy. Scandium combines with aluminum in spherical configuration, producing dispersoids that stabilize the structure, and pushing the strength of aluminum-magnesium-scandium alloys to the level of precipitation-hardened alloys. The Al.sub.3Sc (LI.sub.2) phase forms a fine dispersion of spherical particles, which provides a substantial increase in strength. Scandium reinforced aluminum alloys exhibit a high degree of grain refinement and weld strengthening, a high resistance to hot cracking in welds, and inhibition of recrystallization up to 600.degree. C. [0007]The addition of zirconium reduces the amount of scandium required to strengthen aluminum-magnesium-scandium alloys. Zirconium tends to provide stability to the dispersoids during high temperature operations, thereby maintaining alloy strength. In the absence of zirconium, the Al.sub.3Sc dispersoids tend to grow in size at high temperatures and lose their ability to inhibit recrystallization. [0008]While several aluminum-magnesium alloys with scandium and/or zirconium have been studied, none show the particular composition ranges of the present aluminum alloy. Thus, an aluminum alloy solving the aforementioned problems is desired. SUMMARY OF THE INVENTION [0009]The aluminum alloy is an aluminum-magnesium-scandium-zirconium alloy having a long term corrosion resistance combined with high strength as compared to standard AA 5052 alloy, and is suitable for use in marine and salt water environments with a minimum of corrosion. The aluminum alloy contains about 2.2-3.0 wt. % magnesium, about 0.1-0.97 wt. % scandium, and 0.14-0.9 wt. % zirconium. The alloy may also contain about 0.1-0.4% wt. % iron, 0.001-0.2 wt. % chromium, 0.02-0.94 wt. % titanium, and silicon, copper, zinc and manganese up to about 0.20 wt. %, 0.1 wt. %, 0.1 wt. %, and 0.01 wt. %, respectively, either as additives intentionally added during processing or as impurities, the remainder being aluminum. [0010]Testing has shown that the addition of scandium provides greater strength than aluminum alloys of comparable magnesium content through the formation of fine, evenly distributed aluminum-scandium dispersoids, while the addition of zirconium prevents dispersoid coarsening at elevated temperatures, thereby providing flexibility in forming products with the alloy. Electron microscopy and polarization studies show reduced corrosion upon exposure to salt water, with mainly surface crystallographic pitting. The reduced corrosion is thought to be due, in part, to the formation of a protective boehmite layer on the surface, probably resulting from the fine, homogenous distribution of precipitates in the microstructure of the alloy. The aluminum alloy may be used in cast or wrought form, but is preferably used for the production of high strength, corrosion resistant extruded aluminum products. [0011]These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0012]FIG. 1A is a scanning electromicrograph of an age-hardened aluminum-magnesium-zirconium-scandium alloy (X300) (Alloy 3). [0013]FIG. 1B is a Scanning Electron Microscope/Electron Detector System spectrograph obtained from a precipitate in an aluminum-magnesium-zirconium-scandium alloy (Alloy 3). [0014]FIG. 2 is a transmission electromicrograph showing Al.sub.3Sc precipitates and dislocations at the grain boundaries of an aluminum-magnesium-zirconium-scandium alloy (Alloy 3) according to the present invention. [0015]FIG. 3 is a chart showing the effect of scandium and zirconium addition on the tensile and yield strength of aluminum-magnesium-zirconium-scandium alloys. [0016]FIG. 4 is a graph of the corrosion rate vs. time of various alloys of aluminum with magnesium, scandium and zirconium upon exposure to a 3.5 wt. % solution of NaCl. [0017]FIG. 5 is a chart showing the corrosion rate vs. time of an Al--Mg-0.9% Sc-0.14% Zr alloy upon exposure to a 3.5 wt. % solution of NaCl. [0018]FIG. 6 is a chart showing potentiodynamic polarization curves of various Al--Mg--Sc--Zr alloys in a 3.5 wt % solution of NaCl. [0019]FIG. 7 is an electromicrograph showing crystallographic pitting on the surface of an Al--Mg-0.14% Zr alloy (Alloy 2) upon exposure to a 3.5 wt. % solution of NaCl (X1000). [0020]FIG. 8 is an electromicrograph showing crystallographic pitting on the surface of an Al--Mg-0.15% Sc--Zr alloy (Alloy 3) upon exposure to a 3.5 wt. % solution of NaCl (X1000). [0021]FIG. 9 is an electromicrograph showing mud cracking of a thick non-barrier oxide layer and the formation of pits on the surface of an Al--Mg-0.9% Sc--Zr alloy (Alloy 6) upon exposure to a 3.5 wt. % solution of NaCl (X1000). Continue reading about Aluminum alloy... Full patent description for Aluminum alloy Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Aluminum alloy patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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