OS12F012 Fatigue Crack Propagation Behavior of AZ61 Extruded Magnesium Alloy under Controlled Humidity

Abstract

Fatigue crack propagation (FCP) tests were performed using CT specimens of extruded magnesium (Mg) alloy, AZ61, at a frequency of 10 Hz and stress ratios, R, of 0.05 and 0.7. The FCP tests were conducted in the environmental chamber, in which the humidity was controlled from 20%R.H. up to 80%R.H. The FCP tests were also performed in dry air and pure water for comparison. The effect of humidity on FCP behavior of Mg alloy was investigated. The FCP rates and crack closure behavior were strongly affected by humidity. When the FCP rates, da/dN were evaluated by stress intensity factor, ΔK , the FCP rates in dry air were the lowest irrelevant to the stress ratio. The humidity in air accelerated FCP rates in the low ΔK region even at the lowest humidity of 20%R.H. The FCP rates under the humid conditions were similar to those in pure water. After allowing for crack closure, the effect of environment still existed, where the FCP rates were the fastest at 30%R.H. under R=0.05, then in the higher humid conditions and in dry air, in decreasing order. The acceleration could be attributed to both anodic dissolution and hydrogen embrittlement at the fatigue crack tip.