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When the metal undergoes plastic deformation at high temperature, the microstructure of the material will undergo a series of dynamic changes. The microstructure characteristics of the material directly determine its mechanical behavior, thus controlling its properties. Studying the prediction model of microstructure evolution and rheological stress of materials under different deformation conditions can provide scientific basis and theoretical guidance for reasonably determining the hot working process of materials and controlling product quality. In order to obtain the best process parameters for the thermal processing of ZA270.15Ce alloy, the thermal deformation behavior of ZA270.15Ce alloy at temperatures of 200-320 °C and strain rates of 0.01-10 s−1 is investigated using isothermal constant-rate thermal compression experiments. Comparing the improved Arrhenius model with the backpropagation-deep neural networks (BP-DNN) model for predicted stresses, it is found that the BP-DNN model has higher prediction accuracy with a coefficient of determination of 0.99838. The predicted stress–strain curves are consistent with the experimental results. The process diagram shows that the optimal heat deflection temperature range is in the field of 220-250 °C/0.01-0.03 s−1 and 250-290 °C/0.01-0.22 s−1. No instability, such as cracking, is found in the best heat deformation zone. The percentage of recrystallization in the unsuitable zone is lower than in the optimal zone, and it has a higher dislocation density. Part of the low-angle grain boundaries absorbed dislocations are converted into high-angle grain boundaries. Therefore, the results determined by the thermal processing diagram are consistent with the actual microstructure. The hot working construction of ZA270.15Ce alloy can enable optimal control of the preparation process. [ABSTRACT FROM AUTHOR]

Mg–8.7Gd–4.18Y–0.42Zr magnesium alloys are subjected to hot compressive tests at a strain rate of 0.002–2 s−1 and a compression temperature of 300–450 °C. Compared with strain rate, compression temperature appears to have a greater impact on dynamic precipitation. By virtue of the pinning effect, precipitates located immediately adjacent to the dynamic recrystallized (DRX) grain boundaries may greatly affect grain growth. As the compression temperature increases, DRX grains multiply rapidly. Nevertheless, the number of DRX grains is decreased owing to the increase in strain rate. However, further increasing the strain rate to 2 s−1, the increased energy stored generates stronger driving forces, causing dislocations to move, thereby raising the number of DRX grains by a considerable amount. With an increase in compression temperature and a decrease in strain rate, substructure development has been described as high-density dislocation → VLAGBs (sub-GBs) → LAGBs → HAGBs → DRX grains. It is DRX that is responsible for the predominant softening mechanism in this studied alloy, accompanied by a continuous dynamic recrystallization (CDRX) process characterized by transforming low-angle grain boundaries into high-angle grain boundaries, as well as discontinuous dynamic recrystallization (DDRX), which is characterized by bulging grain boundaries. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Mg-8.7Gd-4.18Y-0.42Zr alloy was investigated by uniaxial hot compression tests at 300–475 °C with strain rates of 0.002–10 s−1. The average activation energy was calculated as 227.67 KJ/mol and a constitutive relation based on the Arrhenius equation was established in this study. The results show that Mg-8.7Gd-4.18Y-0.42Zr magnesium alloy is a strain rate and temperature-sensitive material. When the temperature is constant, the flow stress increases with the increase of strain rate, while when the strain rate is stable, the flow stress decreases with the increase of temperature. DRX is the main softening mechanism of the alloy, including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Meanwhile, the DRX grains nucleate preferentially at the twin intersections in the parent grains under the deformation condition below 300 °C and gradually expand outward with the increase of strain. When the compression temperature is above 400 °C, DRX grains nucleate preferentially at the original grain boundary and then gradually expand inward with the increase of strain. The optimum deformation conditions of the studied alloy are performed at 400–450 °C and 0.002–0.02 s−1 by a comprehensive comparison of the hot processing map, microstructure refinement, and formability. [ABSTRACT FROM AUTHOR]

Basing on the concept of processing rote design and the compositional design, a good combination of strength and ductility in a Cu–9Ni–6Sn-0.2Nb alloy was successfully achieved by the combination of Nb addition, pre-annealing and the subsequent aging treatment. The microstructure evolution, mechanical properties and electrical conductivity on the Cu–9Ni–6Sn alloys with Nb addition were investigated in details. The results indicated that NbNi 3 particles efficiently suppressed the growth of recrystallized grains in the Cu–9Ni–6Sn-0.2Nb alloy and fined grains were achieved during pre-annealing treatment, the grain size being refined from ∼49.5 μm to ∼2.5 μm. After aging treatment, an optimal combination of ultimate tensile strength 1000 MPa, yield strength 825 MPa, elongation 13%, Vickers hardness 300 HV and electrical conductivity 13.1 %IACS were attained in the Cu–9Ni–6Sn-0.2Nb alloy by 80% cold-rolling, pre-annealing at 850 °C for 3 min and aging at 350 °C for 10 h. Especially a good strength with excellent elongation was firstly achieved in Cu–Ni–Sn alloys via the combination of Nb addition, pre-annealing and aging treatment in this study. Strengthening mechanism has been quantitatively established, indicating that the grain boundary and precipitation strengthening play important roles in enhancing the yield strength of the alloy with Nb addition. This study aims to provide a new insight into improving the comprehensive properties of Cu–Ni–Sn alloys, and supplies basis for the microstructure and mechanical property control of the materials. • A Cu–9Ni–6Sn-0.2Nb alloy with good combination of strength and ductility was successfully developed. • There was a significant effect of NbNi 3 phases on suppressing the growth of recrystallization grains. • The optimal property is obtained for Cu–9Ni–6Sn–0.2Nb alloy, for hardness 330 Hv, UTS 1000 MPa, elongation 13 %. • The strengthening mechanisms of Cu–9Ni–6Sn-(0.2Nb) alloys were established quantitatively. [ABSTRACT FROM AUTHOR]

Cu–9Ni–6Sn specimens with different Nb contents ranging from 0 to 0.22 wt% were prepared by a vacuum induction furnace, and needle-like NbNi 3 particles were found at the grain boundaries and interior after solution treatment. The results indicated that these NbNi 3 particles suppressed the discontinuous precipitation (DP) growth during aging treatment. By using Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation and Arrhenius equation, the kinetics of DP is also figured out and the activation energy (Q) of the DP in Cu–9Ni–6Sn- x Nb (x = 0, 0.05, 0.22 wt%) alloys are 75.8 kJ/mol, 80.9 kJ/mol and 88.5 kJ/mol, respectively, indicating that the atom diffusion for producing DP is more difficult in Nb-bearing alloys, and the formation of DP is inhibited correspondingly. What's more, the lamellar spacing (S) of DP increased and the growth rate of DP decreased in the with the Nb-bearing Cu–9Ni–6Sn alloy. • Fine grain sizes are appeared in Nb-addition alloy. • The NbNi 3 particles are observed in Nb-addition alloy. • The DP in Cu–9Ni–6Sn alloy can be suppressed by addition of Nb. • Interlamellar spacing of DP increases with increasing Nb content. [ABSTRACT FROM AUTHOR]