Abstract
Proportional and non-proportional multiaxial fatigue tests are conducted on the closed-die forged ZK60 extrusion. The shear strain amplitude was kept constant at 0.5% for all the tests, while two different axial strain amplitudes of 0.4% and 0.7% were considered. At the higher strain amplitude (0.7%) significant difference was observed between the torque amplitudes of proportional and non-proportional tests, whereas the axial load amplitude responses remained the same regardless of the phase angle shifts. It is likely that as the phase angle changes from 0-90, the twin volume fraction at the peak shear strain decreases resulting in higher torque responses. On the other hand, at the lower strain amplitude, i.e. 0.4%, where twinning is not active, phase angle does not show any effect on the shear response. An energy-based fatigue model is employed that effectively explains the different damage contributions by the axial and torsional loadings at different strain amplitudes, and accurately predicts the proportional and non-proportional multiaxial fatigue lives.
Highlights
Concerns over the adverse impact of high fuel consumption have led the transportation sector to adopt light weight alloys in their products
We investigate the effect of phase angle on the shear response of closed-die forged ZK60 extrusion
This sharp texture is due to the rotational dynamic recrystallization (RDRX), which causes the hexagonal closed pack (HCP) grains to rotate [17][13]
Summary
Concerns over the adverse impact of high fuel consumption have led the transportation sector to adopt light weight alloys in their products. Die-casting is the dominant processing method of Mg alloys for its economic benefits [2]. It makes a lot of defects and porosities in the microstructure of the material, which adversely affects its mechanical behaviour. Wrought Mg alloys are gaining interests to be utilized for their higher strength and finer grains [3]–[5]. The multiaxial fatigue characteristics of different wrought Mg alloys have recently been investigated. The effect of phase angle on the mechanical behaviour of these alloys are studied, and it was reported that the non-proportionality has no effect on their fatigue life [6]–[9]. An energy-based model is employed that can accurately predict the proportional and nonproportional fatigue lives
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