Effect of pre-corrosion on the fatigue fracture behavior of ER8 wheel steel

The salt spray pre-corrosion test was carried on the fatigue specimens of ER8 wheel steel, and then fatigue experiment with a stress ratio (R) of 0.1 was conducted. The fractures were characterized by field emission scanning electron microscopy. The results show that pre-corrosion significantly reduces the fatigue limit of the rim material, the main crack-induced fracture mechanism occurs under pre-corrosion conditions for 6 h at a lower stress, and the fracture mechanism of multi-crack interactions occurs at a higher stress after pre-corrosion for 48 h. For pre-corrosion fatigue test, cracks originate from pitting pits. Then, multiple fatigue crack nucleations expand from different orientations in the transgranular fracture mode, forming cleavage facets.

Plane Bending Fatigue in TIG and MIG Welds of Non-Combustible Magnesium Alloy

Fatigue strength tests were carried out under plane banding loading with different stress ratio in Mg-Al-Ca-Mn alloy and its TIG and MIG welds. The welds showed lower fatigue strength compared to the base material. Weld defects were observed as fatigue crack origins in both TIG and MIG welds. It was speculated that difference in size of weld defect and multiple cracking occurred in MIG weld might affect fatigue strength characteristics in the welds. Effect of stress ratio on fatigue strength at 107 cycles was not significantly observed in fatigue test results obtained with different stress ratio in the base material and the welds. Scatter in size and distribution of weld defect could influence fatigue fracture behavior in the welds.

Effect of Si Content on the Fatigue Fracture Behavior of Wrought Al-xSi-0.7Mg Alloy

The wrought Mg-containing high-silicon aluminum alloy has become more attractive as an ideal structural material, because it has moderate strength and the ductility, high wear and corrosion resistance, low thermal expansion coefficient and low cost. However, as structural material, the fatigue properties and the fatigue fracture behavior of it should be paid much more attention to, especially the effect of Si content on the fatigue properties of wrought Mg-containing Al-Si alloy. In this paper, the wrought Al-(1.44%, 4.92%, 6.61%, 8.81% and 12.4%)Si-0.7%Mg alloy were prepared through DCC and homogenization treatment, and then hot-rolled and cold-rolled into 1.3mm sheets. The microstructure and fatigue fracture morphology of Al-(1.44~12.4)Si-0.7Mg-T4 alloy sheet after fatigue test were investigated by LSCM and SEM. The results showed that the size of Si particles in Al-(1.44~12.4)Si-0.7Mg alloy sheets was approximately the same, but the number of Si particles increased as the Si content increased. The size of recrystallization grain in Al-(1.44~12.4)Si-0.7Mg alloy sheets decreased from 47μm to 10μm when Si content increased from 1.44% to 12.4%, which indicates that increasing of Si content can refine the grain of Al-(1.44~12.4)Si-0.7Mg alloy sheets. With the increasing of Si content the propagation area of fatigue fracture surface of Al-(1.44~12.4)Si-0.7Mg alloy sheets in T4 temper became rougher, and crack propagation became more difficult. Moreover, dimples in the fast fracture area became larger in amount, smaller in size and more uniform in distribution.

Orientation Dependence on Fatigue Fracture Behavior of Pure Mg Single Crystals

It is well known that magnesium (Mg) shows anisotropic fatigue behavior. However, the fatigue mechanisms have yet to be elucidated. The relationships between crystal orientations and crack initiation behavior in Mg single crystals were investigated by uniaxial tension-compression fatigue tests. Three types of round-bar specimens were prepared. The lording direction of AD, BC and EF specimen were [110], [100] and [0001], respectively. Fatigue tests were carried out with the stress ratio R=-1 and the frequency of 10Hz at room temperature in laboratory air. At stress amplitude (σa) over 40 MPa, fatigue lives of BC specimen and EF specimen were the longest and shortest. However, at σa =20 MPa, the fatigue life of all specimens were almost the same. It was found that fatigue lives of Mg single crystals strongly depend on crystal orientations and stress.