Role of loading direction on cyclic behaviour characteristics of AM30 extrusion and its fatigue damage modelling

Abstract

a b s t r a c tAnisotropic fatigue and cyclic behaviour of AM30 Mg alloy extrusion is investigated by performing fullyreversed strain-controlled tension-compression cyclic tests at strain amplitudes between 0.3% and 2.3%, along extrusion (ED) and transverse (TD) directions. The shapes of half-life hysteresis loops suggest the predominance of slip and twinning/de-twinning mechanisms below and above the strain amplitude of 0.5%, respectively. The twinning/de-twinning occurrence is found to be more extensive during straining along ED, which results in higher asymmetry of hysteresis loops, and thereby, higher induced mean stress. This adversely affects the fatigue resistance and yields to less number of cycles before failure in ED. Optical microscopy and texture analysis are employed to validate the findings. In addition, fracture surfaces are studied by scanning electron microscopy to identify the sources of fatigue crack initiation. Persistent slip bands (PSBs) and twin lamellae interfaces are evidenced as crack initiation sites at low and high strain amplitudes, respectively. Cracks emanated from debonded inclusion interface are also observed. Lastly, estimated fatigue life by Smith-Watson-Topper (SWT) and Jahed-Varvani (JV) fatigue models are compared with experimental life obtained through this study as well as the ones reported in the literature. The JV energy model is proven to yield better life predictions.

Fatigue of Magnesium-Based Materials

“…(3) Figure 6. Cyclic hysteresis loops of AZ31B, AZ61A, AM30 and ZK60 magnesium extrusions [15][16][17][18]. Figure 7.…”

Multiaxial fatigue of extruded ZK60 magnesium alloy

“…[4][5][6][7] Texture evolution in the microstructure of extruded magnesium alloys is prevalent, and the effect of this texture on the deformation and mechanical behavior of ZK60A is well established in the literature. 1,[8][9][10] From metallurgical stand point, the development of strong texture in wrought magnesium alloys such as AZ31, [11][12][13] AZ61, 14 AZ80 and ZK60, 15 and AM30 16,17 usually results in a highly irregular microstructure with distributed grain sizes. Nonetheless, grain refinement through different heat or mechanical treatment, severe plastic deformation, or surface treatments such as shot peening have been shown to enhance mechanical performance of the alloy.…”

Improving Corrosion and Corrosion-Fatigue Resistance of AZ31B Cast Mg Alloy Using Combined Cold Spray and Top Coatings

“…In general, wrought Mg alloys exhibit superior mechanical properties relative to as-cast materials [7][8][9]. However, the limited slip systems in Mg alloys at room temperature reduce their formability and hence complex-shaped parts cannot be made [2].…”