微量Ce对细化A356合金初生相的作用

利用低过热度浇注技术制备了半固态A356-Ce合金浆料,研究了稀土Ce对半固态A356合金的初生相形貌和尺寸的影响.研究结果表明:含有适量稀土Ce的A356铝合金经低过热度浇注可制备具有颗粒状和蔷薇状初生相的半固态浆料,合金熔体等温温度会影响Ce细化半固态A356合金中初生相的效果.Ce对半固态A356铝合金的初生相细化机理与稀土在铝合金中诱发的共晶反应有关.      

Microstructure evolution during reheating of extruded Mg-Gd-Y-Zr alloy into semisolid state

The microstructure evolution of an extruded Mg-8.57Gd-3.72Y-0.54Zr (mass fraction, %, GW94) alloy during reheating into the semisolid state was investigated using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Typical semisolid microstructure with globular solid particles distributed in the liquid matrix is obtained over 600 °C. The solid content of (Gd+Y) in the primary a-Mg particles decreases with increasing the semisolid temperature. With the prolongation of isothermal holding time, the liquid fraction does not change significantly, while the grains grow up and spheroidize. Three methods used to determine the liquid fraction as a function of temperature, namely quantitative metallography on quenched microstructures, cooling curve thermal analysis, and thermodynamic calculations were further compared.     

Numerical simulation on electromagnetic field,flow field and temperature field in semisolid slurry preparation by A-EMS

A two-dimensional computational model coupling an annular electromagnetic stirring (A-EMS) with a macroscopic heat and fluid flow analysis in Al-alloys semisolid slurry preparation was developed. The dynamic evolutions of the electromagnetic field, flow field, and temperature field were presented successfully by commercial software ANSYS 10.0 with corresponding experimental verification. A horizontally rotational electromagnetic field and, thereby, a more intensive velocity field were uniformly distributed in the stirred melt even at commercial frequency, and thus, a lower temperature difference in the stirred melt and subsequent uniformly fine microstructures were obtained compared with the normal electromagnetic stirring. The simulation results were in good agreement with experimental ones.     

Preparation of semi-solid AlSi7Mg alloy slurry with big capability

Semi-solid AlSi7Mg alloy slurry was prepared by low superheat pouring and weak traveling-wave electromagnetic stirring.The effects of pouring temperature and stirring power on the microstructure of AlSi7Mg alloy slurry were studied.The results show that the semi-solid AlSi7Mg alloy slurry of 5 kg can be prepared.This new technology can save energy and make the pouring process convenient.When the pouring temperature is decreased at a stirring power of 0.41 kW,the shape of primary α-Al grains gradually changes from dendritic-like to spherical.When the alloy melt is poured at the temperature(630°C) with a certain superheat,the pouring process becomes easier,and the spherical microstructure of AlSi7Mg alloy slurry can be prepared by the weak traveling-wave electromagnetic stirring.When the pouring temperature is 630°C,increasing the stirring power appropriately can result in better spherical primary α-Al grains,but if the stirring power is increased to a certain value(1.72 kW),the shape of primary α-Al grains does not obviously improve when the stirring power is continually increased.     

60Si2Mn弹簧钢半固态坯料制备的实验研究

利用自制的高熔点半固态坯料装置制备了具有触变特性的60Si2Mn钢半固态坯料,并通过观察淬火金相,分析了搅拌工艺参数、稀土元素及冷却速度对半固态组织的影响.结果表明:搅拌功率与搅拌频率对初生相凝固形态影响显著;在一定搅拌频率范围内,随搅拌功率增大,初生奥氏体组织得到了充分细化和均匀球化;稀土元素的加入增大了形核率并抑制了晶粒长大,进而影响半固态晶粒形态;加大降温搅拌冷却速度有助于晶粒的细化.     

New technique for preparing A356 alloy semisolid slurry and its rheo-diecast microstructure and properties

A new technique for preparing semisolid slurry, namely, distributary-confluence runner (DCR), was combined with die-casting (DC) to conduct rheological die-casting (R-DC) of A356 alloy. The mechanism of DCR for semisolid slurry preparation was determined via numerical simulations and experiments. The microstructure and mechanical properties of A356 alloys prepared via DC and R-DC were studied. High-quality slurry containing numerous primary α-Al (α₁-Al) with an average size of 49 μm and a shape factor of 0.81 could be prepared via DCR. Simulation results indicated that the unique flow state and physical field changes during slurry preparation were conducive to accelerating the uniformity of melt temperature and composition fields, nucleation exfoliation, and spherical growth. Compared with the alloy prepared via DC, the tensile strength, yield strength, and elongation of A356 alloy prepared via R-DC increased by 19%, 15%, and 107%, respectively.     

半固态金属成形的研究概况和应用

对半固态加工技术进行了简要的归纳,讨论并分析了其关键技术问题和发展方向.对半固态加工的工艺原理、浆料制备方法和成形工艺进行了说明,阐述了其技术优势和应用;半固态合金成形是一种具有非枝晶组织特征和触变性能的近终形加工技术,有利于环境保护和可持续发展,在汽车、计算机、通讯、航空、航天以及国防等尖端领域,都将具有广阔的发展和应用前景.     

半固态加工技术的进展及我国应对措施

半固态金属成形技术具有高效、节能、近终形生产和成形件性能高等许多优点，被专家们称为21世纪最具前景的加工方法。本文介绍了半固态金属成形的成形工艺、坯料制备工艺、微观组织、数值模拟状况及国内外研究应用情况，展望了半固态金属 的前景，提出了我国的应对措施，     

Globulization mechanism of the primary Al of Al−15Cu alloy during slurry preparation for rheoforming

Semisolid slurries of Al-15Cu alloy were produced for rheoforming by a low temperature pouring technique. To investigate the morphological change of the slurry in terms of the particle mean diameter and the roundness factor, samples were extracted during the continuous cooling and the isothermal holding stage of the slurry by a simple technique of interrupt quenching. Results demonstrated that the fine-grained equiaxed dendritic structure, which formed during low temperature pouring, is changed to a globular structure when held at a semisolid temperature for sufficiently long holding time. With regard to the globulization mechanism of the primary α-phase, local melting is considered to take place at the neck of equiaxed dendrites, leading to the separation of small new particles during continuous cooling. These newly formed particles eventually grow during isothermal holding in the semisolid temperature by obeying theD ³=Kt kinetic law, which suggests coarsening by Ostwald ripening.     

半固态模锻变形机制研究

通过帽形件的半固态模锻成形,阐述了半固态浆料变形的物理模型,研究了半固态浆料变形过程及变形机制。实验表明:半固态浆料模锻成形的变形方式是不同的,不同的固相率下其固液两相的塑性流动机制也是不同的;而且制件不同部位的微观组织形貌也有差异。