PLC (Portevin-Le Chatelier) effect, as a plastic instability phenomenon, often appears in aluminum alloys, especially in 5xxx AlMg alloys. The microscopic mechanism of PLC effect is due to dynamic strain aging, which is manifested in the serrated flow in stress-strain curves. Therefore, the appearance of PLC effect will obviously affect the stress-strain behavior of the material. When the precipitates present in the material, the PLC effect will change due to the interaction between precipitates and dislocations, and the stress-strain behavior of the material will become more complex. It is still not clear how the precipitates affect the flow stress of the material by influencing the PLC effect.
Prof. Haowei Wang’s team, from the Institute of Special Materials of Shanghai Jiao Tong University, had studied the effect of PLC effect on the flow stress in the presence of small shearable and large non-shearable precipitates, respectively, through a combination of modeling and experiment. In this study, the small angle neutron scattering (SANS) technique provided by Prof. Shengyi Zhong quantitatively characterized the size and volume fraction of precipitates, which provided key technical support for the design and control of shearable and non-shearable precipitates
Figure 1 Characterization on Al3(Sc, Zr) precipitates by TEM and SANS
The results show that the proportion of PLC-induced strengthening in the total flow stress can reach 14.5% for AlMg alloy. When the shearable precipitates and large non-shearable precipitates are introduced, this proportion decreases to 4.5% and 9.5%, respectively, which indicates that the introduction of precipitates (especially the shearable precipitates) can significantly weaken the influence of PLC effect on the flow stress. Since the appearance of PLC phenomenon often deteriorates the surface quality and decreases the processing performance of the material, thus the PLC effect is expected to be suppressed or disappeared. This study indicates that the PLC effect of materials can be suppressed by introducing small shearable precipitates, which can provide the insight for the design of new materials.
Figure 2 The proportion of PLC-induced strengthening in the total flow stress: (a) AlMg; (b) AlMgScZr containing shearable precipitates; (c) AlMgScZr containing non-shearable precipitates; (d) comparison of the three alloys
This study was published in Acta Materialia, a top journal in the field of metal materials, based on "Quantitative assessment of the influence of the Portevin-Le Chatelier effect on the flow stress in precipitation hardening AlMgScZr alloys". The first author of the paper is Dr. Han Chen. The corresponding authors are Prof. Zhe Chen and Prof. Shengyi Zhong. During this research, Prof. Yves Brechet, Dr. Gang Ji and Dr. Guanyun Yan gave a lot of experimental support and key discussions. This research was supported by the National Key Research and Development Program (2021YFA1600900), the National Natural Science Foundation of China (No. 51971137) and the China Postdoctoral Science Foundation (2022M722046).
Paper link：https://www.sciencedirect.com/science/article/pii/S1359645423003919
