과시효열처리한 Al-4.2Zn-1.8Mg 합금의 피로균열전파에 관한 고찰

A Study on the Overaging Treatment the Fatigue Crack Propagation of Al-4.2Zn-1.8Mg Alloy

This study is to investigate the effect of heat-treatment on fatigue crack propagation. Three types of heat-treatment were used to study the effect of heat-treatment on the mechanical properties in Al-4.2Zn-1.8Mg alloy. The three heat-treatment conditions are peak-aged(T6) and over-aged(T7), respectively. Mechanicai properties sush as yield strength and tensile strength were observed to be more superior in TMT conditions the other conditions. (1) TMT condition exhibited the highest tensile strength and the peakaged condition followed, (2) △Kth was 6.3 MPa√m for the peakaged condition, 4.6 MPa√m for TMT condition, and 4.51 MPa√m for the overaged condition, (3) Fatigue crack propagation resistance of the peakaged condition was obviously higher for low and intermediate levels of △K, but indifferent for high level of △K.