Authors: Atef S. Hamada, L. Pentti Karjalainen, Mahesh C. Somani, R.M. Ramadan
Abstract: The hot deformation behaviour of two high-Mn (23-24 wt-%) TWIP steels containing 6
and 8 wt-% Al with the fully austenitic and duplex microstructures, respectively, has been
investigated at temperatures of 900-1100°C. In addition, tensile properties were determined over the
temperature range from -80 to 100°C. It was observed that in spite of the lower Al content, the
austenitic steel possessed the hot deformation resistance about twice as high as that of the duplex
steel. Whereas the flow stress curves of the austenitic steel exhibited work hardening followed by
slight softening due to dynamic recrystallisation, the duplex steel showed the absence of work
hardening and discontinuous yielding under similar conditions. Tensile tests at low temperatures
revealed that the austenitic grade had a lower yield strength than that of the duplex grade, but much
better ductility, the elongation increasing with decreasing temperature, contrary to that for the
duplex steel. This can be attributed to the intense mechanical twinning in the austenitic steel, while
in the duplex steel, twinning occurred in the ferrite only and the austenite showed dislocation glide.
Authors: Xiao Yu Zhong, Guang Jie Huang, Fang Fang He, Qing Liu
Abstract: Uni-axial tensile plastic deformation behavior of rolled magnesium alloy AZ31B under the temperature range from room temperature(RT) to 250°C with strain rates between 10-3 and 10-1s-1 has been systematically investigated. Microstructure evolution and texture were determined using optical microscopy (OM) and electron back-scattered diffraction (EBSD) techniques, respectively. Our results indicated that the strength and elongation-to-fracture were more sensitive to strain rates at elevated temperature rather than that at room temperature; dynamic recrystallization (DRX) and relaxation of stress at elevated temperature resulted in dramatic change of mechanical properties. Compared with strain rate, the temperature played a more important role in ductility of AZ31B Mg alloy sheet.
Abstract: A wrought aluminum alloy 3004 was processed by multi-directional forging (MF), natural aging and artificial aging. The samples possess high strength and high ductility after processing. Grain size in samples was reduced evidently. The strength of samples was enhanced by dispersing ultrafine precipitate particles within the grains, reducing grain-size after MF and aging. The ductility was improved due to reducing the forging stress during aging. Moreover, a dispersing ultrafine precipitate particles widespread within the grains after aging, which helps to accumulate dislocations, increase the dislocation storage capability and resist dislocation slip that lead up to increasing work hardening, the ductility was also enhanced. The tensile strength and ductility of the alloy are 422.4 MPa and 11.95%, respectively.
Authors: Praveen Kumar, Megumi Kawasaki, Terence G. Langdon
Abstract: Ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) may show both enhanced ductility and strength and hence resolve the so-called strength-ductility paradox. To gain mechanistic insights into such resolution, the effect of high-pressure torsion (HPT) on the microstructure and mechanical behavior was studied using a cast Al-7 wt. % Si alloy. As expected, the grain size decreased while the fraction of high-angle grain boundaries and microhardness increased due to HPT processing. However, tensile testing at room temperature revealed a simultaneous increase in strength and ductility compared to the as-cast sample. The samples showing simultaneous increase in strength and ductility also showed an increased contribution from grain boundary sliding (GBS), even at room temperature, which is attributed to the existence of a high fraction of high-angle and high-energy grain boundaries. It is proposed that the occurrence of moderate GBS, providing ductility, in very small size grains provides Hall-Petch strengthening and this suggests a potential combination for simultaneously achieving high strength and high ductility in SPD-processed UFG materials.