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Heat Treatment of Friction-Stir-Welded 7050 Aluminum PlatesA method of heat treatment has been developed to reverse some of the deleterious effects of friction stir welding of plates of aluminum alloy 7050. This alloy is considered unweldable by arc and high-energy-density beam fusion welding processes. The alloy can be friction stir welded, but as-welded workpieces exhibit low ductility, low tensile and yield strengths, and low resistance to stress corrosion cracking. Heat treatment according to the present method increases tensile and yield strengths, and minimizes or eliminates stress corrosion cracking. It also increases ductility. This method of heat treatment is a superior alternative to a specification-required heat treatment that caused the formation of large columnar grains, which are undesired. Workpieces subjected to the prior heat treatment exhibited elongations <2 percent, and standard three-point bend specimens shattered. The development of the present heat treatment method was guided partly by the principles that (1) by minimizing grain sizes and relieving deformation stresses, one can minimize or eliminate stress corrosion cracking and (2) the key to maximizing strength and eliminating residual stresses is to perform post-weld solution heating for as long a time as possible while incurring little or no development of large columnar grains in friction stir weld nuggets. It is necessary to perform some of the solution heat treatment (to soften the alloy and improve machine welding parameters) before welding. The following is an example of thickness- dependent pre- and post-weld heat treatments according to the present method: For plates 0.270 in. (approx.6.86 mm) thick milled from plates 4.5 in. (114.3 mm) thick, perform pre-weld solution heating at 890 F (477 C) for 1 hour, then cool in air. After friction stir welding, perform solution heating for 10 minutes, quench, hold at room temperature for 96 hours, then age at 250 F (121 C) for 5 hours followed by 325 F (163 C) for 27 hours.
Document ID
20100014157
Acquisition Source
Johnson Space Center
Document Type
Other - NASA Tech Brief
External Source(s)
http://www.techbriefs.com/component/content/article/1531
Authors
Petter, George E. (NASA Johnson Space Center Houston, TX, United States)
Figert, John D. (Lockheed Martin Corp. Houston, TX, United States)
Rybicki, Daniel J. (Lockheed Martin Corp. Houston, TX, United States)
Burns, Timothy (Lockheed Martin Corp. Houston, TX, United States)
Date Acquired
August 24, 2013
Publication Date
March 1, 2006
Publication Information
Publication: NASA Tech Briefs, March 2006
Subject Category
Man/System Technology And Life Support
Report/Patent Number
MSC-23472
Distribution Limits
Public
Copyright
Public Use Permitted.

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