Dynamic Recrystallization and Processing Map of Pb-30Mg-9Al-1B Alloy During Hot Compression
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TRADITIONALLY, lead-based alloys, such as Pb-Sn, Pb-Sb, and Pb-Ca, are known as important kinds of electrode materials in lead-acid storage batteries and have been widely investigated.[1–8] In general, to some extent, by adding solutes, such as Sn and Sb, the creep rate of Pb alloys reduces through a favorable solid solution alloying effect, and its fracture behavior also is influenced.[9] However, these Pb alloys are superplastic materials due to the low tensile strength and hardness as well as high elongation. To widen the application of Pb alloys, magnesium, aluminum, and boron were added to these alloys. Therefore, the Pb-Mg-Al-B alloys can be used as X- and c-rays and neutron shielding materials for nuclear radiation; the shielding rates for these materials of 20-mm thickness were 90.29, 99.22, and 97.9 pct for X-ray, with energies of 250, 118, and 65 keV, respectively, 49.75 pct (137Cs) and 34.21 pct (60Co) for c-ray and 92.7 pct for neutron.[10–13] The addition of magnesium in Pb alloy is known to form two eutectics (19.1 at. pct and 83 at. pct Pb) and one intermetallic Mg2Pb (33.3 at. pct Pb).[14] The strong chemical bonds of Mg2Pb and Mg17Al12 result in the mechanical properties of Pb-Mg-Al-B alloy such as
YONGHUA DUAN, PING LI, LISHI MA, and RUNYUE LI are with the Department of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China. Contact e-mail: [email protected] Manuscript submitted January 17, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS A
tensile strength and hardness increase and elongation decrease.[15–17] Thus, low elongation, which is related to the two brittle intermetallics Mg2Pb and Mg17Al12, leads to poor workability at room temperatures and limits the wide application of Pb-Mg-Al-B alloys.[17] The workability at elevated temperatures for some alloys that are difficult to deform can be understood in depth by processing maps based on the dynamic material model (DMM).[18] At high temperatures, large strain can be applied due to the greater amount of activated dislocation slips and the occurrence of dynamic recovery (DRV) and dynamic recrystallization (DRX) during hot deformation. The kinetics of DRV in the alloys with higher deformation resistance, such as austenitic steels, is lower, and DRX can be initiated when the stress is accumulated to the critical value.[19] DRX can bring out reduction in deformation resistance and grain refinement.[20] Therefore, such alloys, including Pb-Mg-Al-B, can only be deformed at elevated temperatures, because there is no apparent flow instability during the deformation process. Therefore, Pb-30Mg-9Al-1B alloy is selected as an example to investigate the DRX behavior and hot workability of Pb-Mg-Al-B alloy with high boron content. In this work, we conducted the hot compression tests of Pb-30Mg-9Al-1B alloy and recorded the true stress–true strain curves under different deformation conditions. We characterized the correlation of flow stress, strain rate, and temperature during hot compression by using the Arrhe
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