Abstract
The low cycle fatigue tests on the crack initiation and propagation of cast magnesium alloys with two small holes were carried out by using in-situ scanning electron microscope (SEM) observation technology. The fatigue crack propagation behaviors and fatigue life, which are affected by two small artificial through holes, including the distances between two holes and their locations, were discussed in detail based on the experimental results and the finite element analysis (FEA). The results indicated that the fatigue multi-cracks occurred chiefly at the edges of two holes and the main crack propagation was along the weak dendrite boundary with the plastic deformation vestiges on the surface of α-Mg phase of cast AM50 and AM60B alloys. The fatigue cracking characteristics of cast AZ91 alloy depended mainly on the brittle properties of β-Mg17Al12 phase, in which the multi-cracks occurred still at the edges of two holes and boundaries of β-Mg17Al12 phase. The fatigue crack initiation position of cast magnesium alloys depends strongly on the radius of curvature of through hole or stress concentration factor at the closed edges of two through holes. In addition, the fatigue multi-cracks were amalgamated for the samples with titled 45° of two small holes of cast Mg-Al alloys when the hole distance is less than 4D (D is the diameter of the small hole).
Highlights
As one of the light metals, the magnesium (Mg) alloys, such as AM50, AM60B, AZ31 and AZ91, have such a high strength-to-weight ratio that they are widely suitable for ultimate weight reduction purposes in automotive and aircraft components as well as other applications [1,2,3]
It has stimulated the substantial interest in understanding their structural integrity and service safety of components by using the magnesium alloys including the microstructural characteristics and mechanical properties in the last decade [6,7,8], enhancing strength and thermal crack resistance of cast magnesium alloys [9,10,11], the improving elongation and low-cycle fatigue (LCF) behaviors of magnesium alloys by means of grain refinement and hot-rolled treatment methods in which the deformation mechanism of AZ31 or AZ91 alloy depends on the grain size [12] and pre-compression deformation process but these magnesium alloys are most
The fatigue data of the cast magnesium alloys (AM50, AM60B and AZ91) under different conditions is shown in Figure 2, where the cases for AM60B and AZ91 were chosen as one of the typical results with two through holes for spacing 1.0 mm, 45◦ tilted to the applied loading direction
Summary
As one of the light metals, the magnesium (Mg) alloys, such as AM50, AM60B, AZ31 and AZ91, have such a high strength-to-weight ratio that they are widely suitable for ultimate weight reduction purposes in automotive and aircraft components as well as other applications [1,2,3]. As most of magnesium alloys are from the foundry and rolling processing technologies, the microstructural defects and other notches of material or structure will inevitably exist in the material interior and surface These alloys have been widely used for the plates with small holes in the automotive and aircraft industry in order to be riveted [4,5]. With enhancing or improving of strength and elongation of cast magnesium alloys, the topics related to fatigue behaviors of cast or semi-solid magnesium alloys, including the fatigue cracking mechanism, fatigue life model, empirical formula of fatigue crack growth rate, reliability evaluation of fatigue data and so forth, have been widely explored
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