Crack initiation mechanism of extruded AZ31 magnesium alloy in the very high cycle fatigue regime

Yang, Fu; Yin, Shuming; Li, S.X.; Zhang, Z.F.

doi:10.1016/j.msea.2008.02.003

Cited by 215 publications

(86 citation statements)

References 20 publications

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“…The investigated alloy displayed a fatigue behaviour comparable or even better than that of other rare earth rich sand cast magnesium alloys; in fact, a fatigue strength of 98 MPa was measured on the AM-SC1 alloy (Mg-Nd 1.7-Other RE 1.0-Zn 0.5 Zn-Zr 0.50 ) [42], while the NZ30K2 alloy (Mg-Nd 2.8-Zn 0.19-Zr 0.50) [12] showed a fatigue strength of 84 MPa (15% lower compared to that measured on the present alloy). It is also worth noting that the fatigue strength of the EV31A alloy used in the present study is comparable with that of the most common wrought magnesium alloy AZ31 [43]. The excellent fatigue response shown by the investigated alloy can be mainly ascribed to the soundness of the specimens, also due to a careful control of the sand casting process; in fact, no solidification defects were detected close to the free surface of the samples, which experiences the maximum stresses, or in the bulk.…”

Section: Fatigue Testssupporting

confidence: 69%

Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation

Ceschini¹,

Morri²,

Angelini³

et al. 2017

Preprint

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Rare earth rich magnesium alloys are used in aerospace and automotive fields because of their high specific strength and good castability. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating are necessary, when they have to be used in humid or corrosive environments. The present study was aimed to evaluate the effect of Plasma Electrolytic Oxidation (PEO) and different surface roughness on the rotating bending fatigue of an innovative Mg alloy, with a high content of Nd (up to 3.1 wt%) and Gd (up to 1.7 wt %). Fatigue tests revealed a 15% decrease in the fatigue strength of the PEO treated alloy with respect to the bare alloy, probably due to the residual tensile stresses induced by the treatment. The effect of surface roughness on the bare alloy was, instead, negligible. The mechanisms of crack initiation were similar in the untreated and PEO treated alloy, with crack nucleation sites located in correspondence of large facets of the cleavage planes.

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Section: Fatigue Testssupporting

confidence: 69%

Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation

Ceschini¹,

Morri²,

Angelini³

et al. 2017

Preprint

View full text Add to dashboard Cite

show abstract

“…When the specimens were subjected to a stress higher than the compressive and tensile yield stress in the load-controlled fatigue test, deformation twins were observed in the extruded magnesium alloys. 3,4,26) In contrast, free deformation twins are observed around the fatigue crack path (within the Fatigue Crack Propagation Behavior of Textured Polycrystalline Magnesium Alloysplastic zone) in the L-T, L-S, and E-R specimens (Fig. 4).…”

Section: Resultsmentioning

confidence: 99%

Fatigue Crack Propagation Behavior of Textured Polycrystalline Magnesium Alloys

et al. 2010

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This paper describes the fatigue crack propagation behavior of rolled and extruded AZ31B magnesium alloys (grain size: approximately 20 and 15 mm, respectively). Fatigue crack propagation tests were performed on center cracked plate tension specimens at a stress ratio of R ¼ 0:1 and a frequency of 10 Hz at room temperature. Loading axes were parallel to the rolling and extrusion directions; fatigue cracks propagated parallel to the transverse direction (L-T specimen of rolled AZ31B), parallel to the short transverse direction (L-S specimen of rolled AZ31B), and perpendicular to the extrusion direction (E-R specimen of extruded AZ31B). The crack growth rate (da=dN) of the L-S specimen was approximately 10 times lower than that of the L-T specimen in the examined stress intensity factor (ÁK) range. Fracture surfaces of the L-T and L-S specimens showed many steps parallel and perpendicular, respectively, to the macroscopic crack growth direction. The plot of the da=dN versus the ÁK range for the E-R specimen shows two regimes with different slopes in the examined ÁK range. The fracture surface was covered by various directional steps independent of macroscopic crack growth direction, and the fracture surface roughness at low ÁK was larger than that at high ÁK. SEM-EBSD observations revealed that the c-axis direction is unfavorable for the fatigue crack propagation in rolled AZ31B magnesium alloy. Free deformation twins were observed around the fatigue crack path in the L-T, L-S, and E-R specimens.

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“…It is believed that the underlying reason for the increase of yield strength and the decrease of ductility after the closed-die forging is the grain refining impact of the process (Figure 2). In fact, the forged alloy is exhibiting higher strength in the wake of its finer grains, thereby higher strength according to the Hall-Petch relation [24]. On the other hand, grain refinement yields higher density of grain boundaries that augments the impedance to the dislocation movement.…”

Section: Microstructure Texture and Hardnessmentioning

confidence: 99%

Fatigue life improvement of cast ZK60 Mg alloy through low temperature closed-die forging for automotive applications

et al. 2018

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Abstract. The influence of low-temperature closed-die forging on the quasi-static and cyclic behaviour of as-cast ZK60 magnesium alloy was investigated. As-cast ZK60 billets were forged at a ram speed of 20 mm/sec and a temperature of 250°C. While the yield strength of the starting alloy was 139 MPa, the forging process improved the yield strength significantly by ~68% to 234 MPa. Moreover, the stresscontrolled push-pull fatigue tests at the stress amplitudes of 140 MPa to 180 MPa revealed that the fatigue life was enhanced by an order of magnitude. Microstructural analyses besides the texture measurements at different locations of the forged part manifested partial grain refinement and texture modification strengthening mechanisms. It is believed that the fatigue life improvement is achieved in the wake of the grain refinement and the subsequent material strengthening.

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Crack initiation mechanism of extruded AZ31 magnesium alloy in the very high cycle fatigue regime

Cited by 215 publications

References 20 publications

Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation

Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation

Fatigue Crack Propagation Behavior of Textured Polycrystalline Magnesium Alloys

Fatigue life improvement of cast ZK60 Mg alloy through low temperature closed-die forging for automotive applications

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