http://english.imr.cas.cn/research/researchprogress/201412/W020141209386112215608.pdf

Enhanced mechanical properties of Mg–Al–Zn cast alloy via friction stir processing

http://library.nmlindia.org/FullText/IJF2604111217.pdf

Fatigue behaviour and fracture mechanism of a rolled AZ31 magnesium alloy

The effect of texture on the low-cycle fatigue behavior of a rolled magnesium alloy, AZ31B, was studied at room temperature. It is shown that the Coffin–Manson and Basquin relationships can be used to describe the fatigue resistance of the alloy. The alloy loaded along the rolling direction exhibits only slightly better low-cycle fatigue resistance than that loaded along the transverse direction, due to the in-plane texture symmetry. The in-plane cases exhibit better fatigue behavior than the through-thickness loading. Neutron diffraction and synchrotron diffraction were employed to assist in making mechanistic understandings for the findings. The fundamental difference in the low-cycle fatigue behaviors between the in-plane and through-thickness loadings is attributed to the different activation sequences of twinning and detwinning mechanisms involved and, particularly, the greater requirement for c-axis compression of the grains during the through-thickness tests. The different activation sequences are essentially determined by the initial crystallographic texture, such that the inverted hysteresis-loop shapes are observed.

The effects of texture and extension twinning on the low-cycle fatigue behavior of a rolled magnesium alloy, AZ31B

Evaluation of low cycle fatigue life in AZ31 magnesium alloy

In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2014.0132

Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth.

In this report, the cyclic deformation behaviour of the die-casting magnesium alloy AZ91 was investigated at constant total strain amplitudes between 1.4×10 −3 and 2×10 −2 at room temperature and at 130 °C. The fatigue life data at both temperatures can be described well by the laws of Manson-Coffin and Basquin. The microstructural investigations performed show the strong influence of several microstructural features on the initiation and propagation of fatigue cracks. In order to understand the fatigue crack propagation behaviour, fatigue tests were interrupted at certain numbers of cycles in order to make replicas of the surface of the samples. It could be verified that crack propagation occurs mainly by the coalescence of smaller cracks. Furthermore, unloading tests, performed within closed cycles, were carried out in order to capture the changes of stiffness during a closed cycle with the aim to ascertain the damage evolution occurring during the fatigue tests and to determine the stresses at which the cracks open and close. The results obtained in this study form the microstructural basis of a life-prediction concept, reported earlier.

B Holzwarth

Papers

Cyclic deformation and fatigue behaviour of the magnesium alloy AZ91

Cyclic Deformation Behavior of the Cast Magnesium Alloy AZ91