This study analyses the mechanism of oxygen increase during the electroslag remelting (ESR) process and proposes a countermeasure to control oxygen content of electroslag ingots. The results show that when the oxygen in the electrode is high, the oxygen in the ingots decreases after the ESR process. However, when the oxygen in the electrode is low, the oxygen in the ingots increases after the ESR process. Oxygen increase is closely related to the slag system that was used during the process. According to the experiment and the theoretical analysis, the [Al]- [O] reaction is the control reaction, and the oxygen content of the ingots is determined by the Al 2 O 3 activity in the slag pool when Al in the electrode is kept constant. Based on this finding, the new slag system that decreases the oxygen content of the electroslag ingot is designed and it contains the following components: 63-67%CaF 2 , 4-6%Al 2 O 3 , 18-22%CaO, 8-12%RE x O y or 43-47%CaF 2 , 4-6%Al 2 O 3 , 18-22%CaO, 8-12%MgO and 18-22%RE x O y .
Deformation of an as-rolled rare earth Mg-2Y-0.6Nd-0.6Zr alloy, at different temperatures, was carried out along the BC (90° anticlockwise rotation of the samples after each ECAP pass) route by equal channel angular pressing (ECAP). The effects of the deformation temperature and the predeformation on the microstructure of the magnesium alloy were determined by the microstructure examination. The slip systems and texture change of the Mg-2Y-0.6Nd-0.6Zr alloy were investigated by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD), after equal channel angular deformation. The results showed that after seven passes of rolling, the grain size in the Mg-2Y-0.6Nd-0.6Zr alloy was refined to approximately 22 µm and the slip occurred mainly by a cylindrical slip and a pyramidal slip. After one pass of ECAP at 340 °C, the internal average grain size was significantly reduced to 11 µm, the cylindrical diffraction intensity clearly weakened, and the pyramidal diffraction intensity increased. EBSD pole figure analysis revealed that the base texture of the rolled Mg-2Y-0.6Nd-0.6Zr alloy weakened from 24.31 to 11.34 after ECAP. The mechanical properties indicated that the tensile strength and elongation of the rolled Mg-2Y-0.6Nd-0.6Zr alloy reached maximum values, when the deformation temperature was 340 °C.
In this work, as-cast rare earth Mg-2Y-0.6Nd-0.5Zr alloy was successfully processed by forging at 350 °C and different numbers of passes of equal channel angular pressing (ECAP) along the Bc route. The effects of ECAP on the microstructure, texture and mechanical properties of a pre-forged Mg-2Y-0.6Nd-0.5Zr alloy were systematically investigated in this paper. The grain size of the alloy was refined from 140 μm to 1.9 μm by forging + ECAP. The alloy has obtained a uniform and fine microstructure under the action of dynamic recrystallization (DRX) during the ECAP process. The forged sample exhibited a strong basal texture. However, the alloy that was processed with ECAP had a tilted texture; the basal orientation was weakened, and the cylindrical and pyramidal orientation was enhanced. An analysis of the mechanical properties showed that the alloy exhibited favorable tensile strength and elongation of 262 MPa and 22.4% after forging and 4 passes of ECAP, which were increased by 118% and 113% compared with the as-cast sample. The alloy strength decreased slightly due to textural transformation and a high degree of recrystallization during ECAP, while the plasticity of the alloy that underwent 6 ECAP passes increased to 25.2%. The results show that the combination processing of forging and ECAP provides a new approach for optimizing the mechanical properties of magnesium alloys.
A fine-grained Mg-2Y-0.6Nd-0.6Zr alloy was processed by bar-rolling and equal-channel angular pressing (ECAP). The effect of ECAP on the microstructure and mechanical properties of rolled Mg-2Y-0.6Nd-0.6Zr alloy was investigated by optical microscopy, scanning electron microscopy, electron backscattered diffraction and a room temperature tensile test. The results show that the Mg-2Y-0.6Nd-0.6Zr alloy obtained high strength and poor plasticity after rolling. As the number of ECAP passes increased, the grain size of the alloy gradually reduced and the texture of the basal plane gradually weakened. The ultimate tensile strength of the alloy first increased and then decreased, the yield strength gradually decreased, and the plasticity continuously increased. After four passes of ECAP, the average grain size decreased from 11.2 µm to 1.87 µm, and the alloy obtained excellent comprehensive mechanical properties. Its strength was slightly reduced compared to the as-rolled alloy, but the plasticity was greatly increased.
The microstructure evolution, texture, mechanical behavior and twin deformation of the ECAPed Mg-2Y-0.6Nd-0.6Zr alloy at liquid nitrogen temperature were investigated by rolling samples. The ECAP processed material appeared the texture of 45 ° to the extrusion direction and its yield strength reached 93.6 MPa. The results showed that cryorolling encourages twinning in Mg-2Y-0.6Nd-0.6Zr alloy, enhancing the tensile strength and texture. Activation of {10-12} twinning during rolling was found to be more pronounced in the cryorolled samples than in the cold rolled samples owing to a lower temperature. As a result, the cryorolled samples had more twins than and cold rolled ones, the proportion of twin areas of room temperature rolling and ultra-low temperature rolling were: 2.445% and 4.234%.
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