Fatigue behaviour of AZ91 magnesium alloy

Abstract

The paper deals with the determination of principal mechanical properties and the investigation of fatigue behaviour of AZ91 magnesium alloy. The experimental material was made by squeeze casting technique and heat treated to obtain T4 state (solution annealing), when hard, brittle Mg17Al12 intermetallic phase is dissolved. The basic mechanical properties (Young’s modulus, ultimate tensile strength, yield strength, elongation to fracture and reduction of area) were determinated by static tensile test. Furthermore, fatigue parameters were investigated and standard tensile curve was compared with cyclic stress-strain curve. The comparison indicates that studied material exhibited cyclic hardening at whole lifetime. In addition, the S-N curve on the basis of smooth test bars tested under symmetrical push-pull loading at room temperature was evaluated. The measured data were subsequently used for assessing the Manson-Coffin curve and for fitting with suitable regression function for determination of the fatigue parameters. Fatigue limit σC of the studied alloy for 108 cycles is approaching 50 MPa. Structure of the studied alloy in the basic state and after heat treatment was observed by light and scanning electron microscopy.