Propagation of short fatigue cracks in permanent and semi-solid mold 357 aluminum alloy

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Journal titleInternational journal of fatigue
Pages120129; # of pages: 9
Subjectaluminum 357 alloy; casting; semi-solid molding; fatigue strength; Microstructurally short crack
AbstractThe high cycle fatigue strengths of aluminum-silicon-magnesium 357 alloy prepared by permanent molding and semi-solid molding are compared at stress ratios R = -1 and R = 0.1. Results show that precipitation hardened permanent mold (PM) and semi-solid mold (SSM) materials have fatigue strengths at R = -1 and 107 cycles of 82 and 113 MPa respectively while those at R = 0.1 are 47 MPa and 78 MPa respectively. Part of this difference is explained by the fact that the SSM specimens contain fewer and smaller defects than the PM specimens. Defects reduce the duration of the short crack propagation period, which significantly affects the overall specimen fatigue life. A comparative analysis of the long crack behaviour indicates that the PM microstructure is more resistant to the propagation of long cracks than the SSM microstructure because crack closure is more significant. However, the long crack behaviour cannot be used to predict the specimen fatigue life, which mainly consists of short crack propagation. Observation of many short cracks using the replication technique indicates that grain boundaries are the most important microstructural barrier to short crack propagation in these materials. The results also show that crack growth decelerations occur at a crack depth comparable in size to the average grain radius of the materials. The difference in the distance of these important microstructural barriers can explain the fatigue strength difference measured. It is concluded that the average fatigue strength is inversely proportional to the square root of the average grain size.
Publication date
AffiliationNRC Industrial Materials Institute; National Research Council Canada
Peer reviewedYes
NRC number53443
NPARC number19434923
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Record identifier8e677f3f-62d7-4c04-8e49-e4419386f6f0
Record created2012-02-17
Record modified2016-05-09
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