大锻件控性锻造过程的计算机模拟技术

提出能够模拟大锻件空洞型缺陷演化和微观组织演变等控性指标的数值模拟方法。基于典型体元模型建立空洞体积变化与宏观应力应变场关系的数学模型,以图从多尺度角度揭示宏观的塑性变形及其应力状态对随机分布的微小空洞的体积变化影响规律。将该模型与有限元法集成,当锻件内任意一点有空洞型缺陷(给定缺陷体积百分比)时,能够模拟得到成形过程中空洞型缺陷的体积变化,从而可被用来评估含缩孔缩松缺陷材料的压实状态。采用元胞自动机方法建立一种转子钢的微观组织演变模拟方法,根据'应变—位错密度—动态再结晶—流动应力'之间的宏微观相互影响规律,模拟出动态再结晶晶粒尺寸和完成分数。将这些模型与热力耦合有限元法相结合,构造大锻件控性锻造过程的数值模拟技术。根据大锻件增量成形的变形特点开发基于刚性区自由度凝聚技术的快速有限元法,从而为大锻件成形的工艺优化提供有效的计算工具。

Effect of process parameters on microstructure and properties of AM50A magnesium alloy parts formed by double control forming

Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.

DETERMINATION OF PRESSURIZING CURVE AND COMPUTER CONTROL OF THICKNESS THINNING FOR SUPERPLASTIC BULGING

This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.

55NiCrMoV7模具钢锻造过程微观组织演化实验与模拟仿真

研究了55NiCrMoV7模具钢棒材镦粗和拔长过程中的微观组织演化规律。结果表明,镦粗过程中棒材心部动态再结晶体积分数达80%,而变形过渡区和死区的动态再结晶体积分数较低;拔长过程中棒材心部发生了二次动态再结晶,过渡区动态再结晶进一步发展,而死区几乎没有发生动态再结晶。基于55NiCrMoV7模具钢在变形温度850~1250℃、应变速率0.001~10 s-1下的金相组织图,建立了动态再结晶临界应变、晶粒尺寸和动力学的数学模型,并通过DEFORM-3D软件建立了棒材镦粗和拔长过程的宏微观耦合有限元模型,研究了棒材温度、应变和组织的分布规律,预测了动态再结晶晶粒尺寸和体积分数值。将预测值与实验值进行了对比,最大相对误差为11.7%。

Improving single pass reduction during cold rolling by controlling initial texture of AZ31 magnesium alloy sheet

The AZ31 magnesium alloy sheets obtained by multi-pass hot rolling were applied to cold rolling and the maximum single pass cold rolling reduction prior to failure of AZ31 magnesium alloy was enhanced to 41%. Larger single pass rolling reduction led to weaker texture during the multi-pass hot rolling procedure. The sheet obtained showed weak basal texture, while the value was only 1/3-1/2 that of general as-rolled AZ31 Mg alloy sheets. It was beneficial for the enhancement of further cold rolling formability despite of the coarser grain size. The deformation mechanism for the formation of texture in AZ31 magnesium alloy sheet was also analyzed in detail.

Cold stamping for AZ31B magnesium alloy sheet of cell phone house

Electric product house of magnesium alloy sheet is usually obtained by warm stamping owing to its poor plasticity and formability at room temperature.The formability of AZ31B magnesium alloy sheet can be improved by repeated unidirectional bending(RUB)process through control of(0002)basal texture.Compared with as-received sheet,the Erichsen value(IE)of the sheet underwent RUB process increases to 5.90 from 3.53 at room temperature.It is also confirmed that cell phone houses could be stamped successfully in crank press with AZ31B magnesium alloy sheets underwent RUB process.It provides an alternative to the electronics industry in the application of magnesium alloys.

Weld Characteristics and NC Bending Formability of QSTE340 Welded Tube

The mechanical characteristics of the weld joint were investigated by tensile test, microstructure test, and microhardness test. The welded tube NC bending tests were carried out to evaluate the weld on the formability of the QSTE340 welded tube. The results show that the wall thinning degree, cross-sectional deformation and springback angle increase significantly as the weld line is located on the outside of the bend compared with that located on the middle and inside, and the welded tubes produce nearly identical performance as the weld line is located on the middle and inside. The wall thickening degree decreases much as the weld line is located on the inside of the bend. So the welded tube can acquire good bending formability as the weld line is located in the region away from the outside of the bend.

Gene editing: an instrument for practical application of gene biology to plant breeding

Plant breeding is well recognized as one of the most important means to meet food security challenges caused by the ever-increasing world population. During the past three decades, plant breeding has been empowered by both new knowledge on trait development and regulation(e.g., functional genomics) and new technologies(e.g., biotechnologies and phenomics). Gene editing, particularly by clustered regularly interspaced short palindromic repeats(CRISPR)/CRISPR-associated protein(Cas) and its variants, has become a powerful technology in plant research and may become a game-changer in plant breeding. Traits are conferred by coding and non-coding genes. From this perspective, we propose different editing strategies for these two types of genes. The activity of an encoded enzyme and its quantity are regulated at transcriptional and post-transcriptional, as well as translational and post-translational, levels. Different strategies are proposed to intervene to generate gene functional variations and consequently phenotype changes. For non-coding genes, trait modification could be achieved by regulating transcription of their own or target genes via gene editing. Also included is a scheme of protoplast editing to make gene editing more applicable in plant breeding. In summary, this review provides breeders with a host of options to translate gene biology into practical breeding strategies, i.e., to use gene editing as a mechanism to commercialize gene biology in plant breeding.

Shape-controlled syntheses of rhodium nanocrystals for the enhancement of their catalytic properties

Rhodium （Rh） is a critical component of many catalysts for a variety of chemical transformation processes. Controlling the shape of Rh nanocrystals offers an effective route to the optimization of their catalytic performance owing to a close correlation between the catalytic activity/selectivity and the surface atomic structure. It also helps to substantially reduce the loading amount and thus achieve a sustainable use of this scarce and precious metal. In this review article, we focus on recent progress in the shape-controlled synthesis of Rh nanocrystals with the goal of enhandng their catalytic properties. Both traditional and newly- developed synthetic strategies and growth mechanisms will be discussed, including those based on the use of surface capping agents, manipulation of reduction kinetics, control of surface diffusion rate, management of oxidation etching, and electrochemical alteration. We also use two examples to highlight the unique opportunities offered by shape-controlled synthesis for enhancing the use of this metal in catalytic applications. The strategies can also be extended to other precious metals in an effort to advance the production of cost-effective catalysts.