- Al-Li
Al-Li alloys are a series of
alloys ofaluminium andlithium , often also includingcopper andzirconium . Since lithium is the least dense elementalmetal , these alloys are significantly less dense than aluminium. Commercial Al-Li alloys contain up to 2.45% lithium.Alloying with lithium reduces structural mass by two effects:
*Displacement- a lithium atom is lighter than an aluminium atom; each lithium atom then displaces one aluminium atom from the
crystal lattice , while maintaining the lattice structure. Every 1% by weight of lithium added to aluminium reduces the density of the resulting alloy by 3%.cite web | last = Joshi | first = Amit | title = The new generation Aluminium Lithium Alloys | work = Indian Institute of Technology, Bombay | publisher = Metal Web News | url = http://www.metalwebnews.com/howto/alloys/alloys.pdf | format =PDF | accessdate = 2008-03-03 ] This effect works up to thesolubility limit of lithium in aluminium.*
Strain hardening - The lithium atom is larger than an aluminium one. Introducing a larger atom into the crystal strains the lattice, which helps blockdislocations . The resulting material is thus stronger, which allows less of it to be used.Al-Li alloys are primarily of interest to the
aerospace industry, due to the weight advantage they provide. They are currently used in a few commercialjetliner airframe s, and theAgustaWestland EH101 helicopter . [Queen's University Faculty of Applied Science, [http://me.queensu.ca/courses/mech412/Notes/aluminum-lithium.doc Aluminium-Lithium Alloys] ]As of 2006 , the third, and current version of the U.S.Space Shuttle 's external tank is principally made of Al-Li. [NASA, [http://www.nasa.gov/centers/marshall/pdf/113020main_shuttle_lightweight.pdf Super Lightweight External Tank] ] In addition, Al-Li alloys are also used on both theAtlas V and Delta IVEELV rockets, and will be used by NASA forProject Constellation , primarily on itsAres I andAres V rockets, as well as theOrion spacecraft .Al-Li alloy
swarf ,scrap and other recycled material must be kept separate from other aluminium streams during recycling, as mixing Al-Li alloy with conventional aluminium recovery streams will cause extreme fire and explosion hazards. [ Patent Storm, [http://www.patentstorm.us/patents/4709740-description.html Direct chill casting of aluminium-lithium alloys] ]ee also
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Aluminium alloy References
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