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This content will become publicly available on January 11, 2019

Title: Influence of friction stir processing on the room temperature fatigue cracking mechanisms of A356 aluminum alloy

Here, failure by fatigue is a common problem associated with cast aluminum alloys due to defects like shrinkage porosities, non-metallic inclusions, etc. Friction stir processing (FSP) has recently emerged as an effective technique for local modification of microstructure. This study investigates the fatigue crack initiation and growth mechanisms in cast and FSPed A356 aluminum alloy. Two sets of parameters were used to friction stir the cast alloy resulting in the complete modification the cast microstructure to a wrought microstructure. Both the FSPed microstructures exhibited severe abnormal grain growth (AGG) after heat treatment leading to a multimodal grain size distribution – the grain sizes ranging from a few microns to a few millimeters. One of the FSP conditions displayed an excellent improvement in fatigue life by an order of magnitude, while the other condition displayed an unexpectedly large scatter in fatigue lives. Detailed study of the fractured fatigue specimens by electron back scattered diffraction (EBSD) revealed that both, fatigue crack initiation and propagation, were intimately tied to the grain size as well as the grain misorientations in the microstructure.
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [3]
  1. Univ. of North Texas, Denton, TX (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. General Motors Technical Center, Warren, MI (United States)
Publication Date:
Report Number(s):
PNNL-SA-130375
Journal ID: ISSN 0921-5093; PII: S0921509318300534; TRN: US1801235
Grant/Contract Number:
AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing
Additional Journal Information:
Journal Volume: 716; Journal ID: ISSN 0921-5093
Publisher:
Elsevier
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Fracture behavior; Fatigue; Grain boundaries; Aluminum alloys; Friction stir welding/processing; abnormal grain growth
OSTI Identifier:
1418022