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University of North Texas

1. Martinez, Nelson Y. Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys.

Degree: 2016, University of North Texas

The Al-Zn-Mg-Cu (7XXX series) alloys are amongst the strongest aluminum available. However, they are considered unweldable with conventional fusion techniques due to the negative effects that arise with conventional welding, including hydrogen porosity, hot cracking, and stress corrosion cracking. For this reason, friction stir welding has emerged as the preferred technique to weld 7XXX series alloys. Aluminum 7449 is one of the highest strength 7XXX series aluminum alloy. This is due to its higher zinc content, which leads to a higher volume fraction of eta' precipitates. It is typically used in a slight overaged condition since it exhibits better corrosion resistance. In this work, the welds of friction stir welded aluminum 7449 were studied extensively. Specific focus was placed in the heat affected zone (HAZ) and nugget. Thermocouples were used in the heat affected zone for three different depths to obtain thermal profiles as well as cooling/heating profiles. Vicker microhardness testing, transmission electron microscope (TEM), and differential scanning calorimeter (DSC) were used to characterize the welds. Two different tempers of the alloy were used, a low overaged temper and a high overaged temper. A thorough comparison of the two different tempers was done. It was found that highly overaged aluminum 7449 tempers show better properties for friction stir welding. A heat gradient along with a high conducting plate (Cu) used at the bottom of the run, resulted in welds with two separate microstructures in the nugget. Due to the microstructure at the bottom of the nugget, higher strength than the base metal is observed. Furthermore, the effects of natural aging and artificial aging were studied to understand re-precipitation. Large improvements in strength are observed after natural aging throughout the welds, including improvements in the HAZ. Advisors/Committee Members: Mishra, Rajiv, Reidy, Rick, Scharf, Thomas, Mukherjee, Sundeep, Du, Jincheng.

Subjects/Keywords: Aluminum 7449; Friction Stir Welding; Tool; Temper; Nugget; Heat Affected Zone; Heat Gradient; Strength; Hardness; TEM; DSC; Artificially Aging; Natural Aging; GP Zones; Engineering, Materials Science; Engineering, Metallurgy; Engineering, Mechanical

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Martinez, N. Y. (2016). Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys. (Thesis). University of North Texas. Retrieved from https://digital.library.unt.edu/ark:/67531/metadc862775/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Martinez, Nelson Y. “Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys.” 2016. Thesis, University of North Texas. Accessed October 26, 2020. https://digital.library.unt.edu/ark:/67531/metadc862775/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Martinez, Nelson Y. “Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys.” 2016. Web. 26 Oct 2020.

Vancouver:

Martinez NY. Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys. [Internet] [Thesis]. University of North Texas; 2016. [cited 2020 Oct 26]. Available from: https://digital.library.unt.edu/ark:/67531/metadc862775/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Martinez NY. Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys. [Thesis]. University of North Texas; 2016. Available from: https://digital.library.unt.edu/ark:/67531/metadc862775/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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