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Metallurgical and Materials Transactions A

, Volume 30, Issue 10, pp 2659–2666 | Cite as

Microstructural effects on high-cycle fatigue-crack initiation in A356.2 casting alloy

  • B. Zhang
  • D. R. Poirier
  • W. Chen
Article

Abstract

The effects of various microconstituents on crack initiation and propagation in high-cycle fatigue (HCF) were investigated in an aluminum casting alloy (A356.2). Fatigue cracking was induced in both axial and bending loading conditions at strain/stress ratios of −1, 0.1, and 0.2. The secondary dendrite arm spacing (SDAS) and porosity (maximum size and density distribution) were quantified in the directionally solidified casting alloy. Using scanning electron microscopy, we observed that cracks initiate at near-surface porosity, at oxides, and within the eutectic microconstituents, depending on the SDAS. When the SDAS is greater than ∼ 25 to 28 µm, the fatigue cracks initiate from surface and subsurface porosity. When the SDAS is less than ∼ 25 to 28 µm, the fatigue cracks initiate from the interdendritic eutectic constituents, where the silicon particles are segregated. Fatigue cracks initiated at oxide inclusions whenever they were near the surface, regardless of the SDAS. The fatigue life of a specimen whose crack initiated at a large eutectic constituent was about equal to that when the crack initiated at a pore or oxide of comparable size.

Keywords

Fatigue Material Transaction Fatigue Crack Fatigue Life Initiation Site 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 1999

Authors and Affiliations

  • B. Zhang
    • 1
  • D. R. Poirier
    • 1
  • W. Chen
    • 2
  1. 1.Department of Materials Science and EngineeringThe University of ArizonaTucson
  2. 2.Department of Aerospace and Mechanical EngineeringThe University of ArizonaTucson

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