Small Fatigue Crack Growth Observations in an Extruded Magnesium Alloy

摘要

The purpose of this paper is to quantify the microstructurally small/physically small crack growth behavior in an extruded AZ61 magnesium alloy. Fully-reversed, interrupted load control tests were conducted on notched specimens that were taken from a magnesium alloy extrusion. In order to measure crack growth, replicas of the notch surface were made using a two-part silicon-rubber compound at periodic cyclic intervals. Scanning electron microscopy analysis of the replica surfaces revealed multi site crack initiation and subsequent crack coalescence. The crack growth behavior of the small fatigue cracks was shown to have a strong dependence on the material microstructure as the crack was submitted to a tortuous growth path along grain boundaries and crystallographic slip planes. A microstructurally dependent crack growth model that was previously developed for FCC metals was further extended here to HCP metals.