4.4 A proposed model of the fatigue behavior of LZ91 dual-phase
Mg-Li alloy
As discussed above, small crack initiation and propagation are highly
affected by the microstructure of the material. Figure 11 thus
presents the schematic illustration of crack initiation and early
propagation process. The stripe phase in white is the α-Mg phase, and
the matrix in blue is the β-Li phase, respectively. Severe plastic
deformation tends to occur in the ‘soft’ phase, i.e., the β-Li phase
during cyclic loading, as shown in Figure 11a. As crack grows and has to
pass through α-Mg grains, the crack propagation will be inevitably
hindered by α-Mg grain due to the hard grain orientations. As a result,
there are some turning points (marked by black arrows) in the crack path
when it passes through α-Mg grains, which make it appear more tortuous.
Eventually, crack continues to propagate, resulting in the final failure
of the material.
In the present investigation, the experimental results and
microstructural analysis of the crack initiation will fill the gap of
our understanding of the VHCF behavior of the dual-phase Mg-Li alloy.
More importantly, they would provide more valuable advice to improve the
anti-fatigue ability of the Mg-Li alloys.