The rotational direction of the friction stir welding (FSW) tool plays a role as important as the weld parameters in FSW processes for magnesium alloys. The formation quality of the weld joints strongly relies on the rotational direction of the stir tool. Based on the present results the better tensile properties of the weld joints are achieved by welding at a higher rotational speed no matter what direction the stir tool rotates. The face bend properties are superior to the root bend properties of the joints. The optimal weld parameters are 1500 rev min 21 /90 mm min 21 and 1200 rev min 21 /60 mm min 21 for the clockwise and counterclockwise directions of the stir tool respectively. Regardless of the direction which the tool rotates in, fractures of the tensile specimens are mostly located at the boundary between the thermal mechanical affect zone and the nugget zone.

Nanostructured bainite was obtained in high-carbon Si-Al-rich steel by low-temperature (220–260 °C) isothermal transformation after austenitisation at different temperatures (900 °C, 1000 °C, and 1150 °C). Improved strength-ductility-toughness balance was achieved in the nanostructured bainitic steel austenitised at low temperatures (900 °C and 1000 °C). Increasing the austenitising temperature not only coarsened prior austenite grains and bainite packets, but also increased the size and fraction of blocky retained austenite. High austenitising temperature (1150 °C) remarkably decreased ductility and impact toughness, but had a small effect on strength and hardness.

The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite.