Effect of Heat-Treating on Microstructure and High Cycle Bending Fatigue Behavior of AZ91 and AZE911 Magnesium Alloys

Abstract

This article investigates the influences of heat-treating on the microstructures and the high cycle fatigue (HCF) properties of AZ91 and AZE911 (AZ91 + 1%RE) magnesium alloys. For such an objective, AZ91 and AZE911 alloys were used after solution treatment at 415°C for 5 hours aged at 215°C for 3 hours and at 215°C for 5 hours, respectively. To investigate the HCF behavior, a rotational bending fatigue test was performed with stress ratio (R) −1 and frequency of 100 Hz at room temperature. Optical microscopy (OM) study demonstrates that heat treatment leads to a reduction in grain size and transformation of continuous and discontinuous precipitations into needle-shaped precipitations, which are located on the grains of the alpha phase. Scanning electron microscopy (SEM) showed both marks of quasicleavage and cleavage on the fracture surface of specimens. These planes indicated the brittle behavior of the fracture. Moreover, in heat-treated specimens, the size of cleavage patterns was smaller, and microcracks were shorter. These behaviors affected the strength of the material and the fatigue lifetime. The results of mechanical tests show a negligible influence of heat-treating on the HCF behaviors of AZ91-T6 and AZE911-T6 alloys. Stress-lifetime curves (S-N) show an increase in fatigue strength in 3.8 × 105 fatigue cycles, from 95 MPa to 125 MPa for the AZ91-T6 alloy and from 125 MPa to 155 MPa for the AZE911-T6 alloy, after heat treatment.

Amazing epsilon-shaped trend for fretting fatigue characteristics in AM60 magnesium alloy under stress-controlled cyclic conditions at bending loads with zero mean stress

“…Then, as a result, the majority of fatigue cracks begin close to the surface. Of course, this result was indicated by Nascimento et al [41] and Oliya et al [29]. Additionally, fretting fatigue cracks are also produced in this region because the contact stresses have their largest local values near the contact surface due to stress concentration.…”

“…Moreover, in Fig 5 , curve fitting was utilized to identify the material properties. It is possible to represent the link between the fatigue lifetime and the stress amplitude, based on the following equation [ 29 ]: …”

“…The loading frequency setting of 6000 rpm (100 Hz) is quite near to the working condition under rated-power for engines in automobiles [ 27 , 28 ]. The fatigue lifetime testing limit was determined to be 1 million loading cycles [ 29 ]. Additionally, the reproducibility or repeatability of the experiment was evaluated using three standard samples (at least) under each value of the stress level.…”

Impact of Corrosion in Simulated Body Fluid on Fatigue Characteristics of 3D-Printed Polylactic Acid-Coated AM60 Magnesium Alloys

“…Fatigue tests were performed for samples under 4 stress levels of 80, 100, 120, and 140 MPa, with a repeatability of 3 tests for each sample. The fatigue limit of magnesium was considered to be 60 MPa after 1 million cycles [41].…”