化学细化半固态Al-Si合金表观黏度及组织分析

为研究化学晶粒细化法对半固态Al-Si合金流变行为的影响,分别添加了Al-5Ti-B、K2TiF6、K2TiF6 石墨以及K2TiF6 Ti细化剂,在合金固化过程中利用Couette同轴圆筒式黏度计测量其表观黏度的变化,并观测不同固相分数试样微观组织.研究表明,化学晶粒细化法大大减小了半固态Al-Si合金的表观黏度,Al-5Ti-B细化效果好于K2TiF6,石墨或Ti和K2TiF6的组合较单一的K2TiF6效果显著.     

Partial Remelting of Thixotropic Magnesium-Rare Earth Alloy from Near Non- Equilibrium- Liquidus Casting

After the investigation on partial remelting of thixotropic magnesium serial alloys （ZK60） by near non-equilibrium liquidus casting （NNLC）, the primary solid grains of ZK60-2Ca alloy spheroidized notably during partial remelting processing, however, coarsening and polygonization as occurred holding time prolonged. The refining and globularity of the thixotropic alloys are promoted after further alloyed by Y, RE, Nd and/or Ag, and the results vary with those addition. The remelting structure of ZK60-2Ca-1Y alloy is finer than its base alloy. And the effect of RE, especially Ag, on the refinement of microstrueture is notable, but Nd does nothing on it. There is little impact of remelting temperature fluctuation on partial remelted microstrueture as holding time in general. On the contrary, it is more sensitive at longer holding time. The quality thixotropic silver-contained alloy can be achieved by remelted partially at 600℃ for 10 min.     

SCR技术半固态制浆及组织形成机理

采用单辊搅拌冷却技术(Shearing-Cooling-Rolling,简称SCR)制备A2017合金半固态浆料,对SCR工艺参数对半固态浆料组织的影响以及组织形成机理进行了研究.结果表明,熔体浇注温度和辊靴型腔高度对半固态浆料组织的影响显著,降低熔体浇注温度或减小辊靴型腔高度,半固态浆料组织从粗大的枝晶和菊花晶转变为细小的等轴晶或球形晶.组织形成机理分析表明,熔体首先在工作辊和靴子表面形核生长,在液流冲击及剪切搅拌的作用下晶核脱落游离进入残余液相区长大成菊花晶,在强烈剪切搅拌作用下,菊花晶断裂破碎最终形成非枝晶组织.     

Semi-solid slurry preparation and rolling of 1Cr18Ni9Ti stainless steel

The preparation and rolling of the semi-solid slurry 1Cr18Ni9Ti stainless steel were researched. The experimental results show that when stirred for 2-3 min under the given test condition, the semi-solid slurry with about 50%-60% (volume fraction) solid and the spherical primary austenitic grains in the size of 100-200μm can be obtained, and it is easy to be discharged from the bottom little hole of the stirring chamber. The semi-solid slurry of 1Cr18Ni9Ti stainless steel can be rolled into the given plate successfully. However, the solid phase and liquid phase are easily separated in the rolling process, so that the solid primary austenitic grains are concentrated in the center and the liquid phase is near the edge of the rolled plate. The strengths of the plate rolled in the semi-solid state are higher than that of the traditionally repeated hot-rolled plate of 1Cr18Ni9Ti stainless steel.     

Al-4Cu-Mg合金半固态压缩时微观组织的计算模型

研究了Al-4Cu-Mg合金半固态压缩变形过程中微观组织参数的变化.结合模糊数学和人工神经网络理论,以Al-4Cu-Mg合金半固态压缩变形时的变形温度、变形程度和应变速率为输入参数,以变形后的晶粒等效直径或分形维数为输出参数,建立了Al-4Cu-Mg合金半固态压缩时的微观组织计算模型.研究结果表明,计算结果与实验结果吻合较好.因此,应用本模型可对Al-4Cu-Mg合金半固态成形过程中的微观组织演变进行预测,为优化变形工艺参数提供了简便、适用的方法.     

Performance of Semi-solid Slurry Produced by Twin-screw Stirring Mixer and Rheo-diecasting Process of AZ91D Alloy

The microstructure of semi-solid slurry of AZ91D alloy, which was produced by twin-screw stirring mixer under the different parameters, was investigated. Rheoforming by cold chamber die casting process was performed thereafter. The results indicate that with decreasing of the barrel temperature of the mixer and the pouring temperature of molten Mg alloy, the solid fraction of semi-solid slurry increases and the size of non-den-dritic grains becomes smaller. While the shear rate increases, the solid fraction of semi-solid slurry decreases. The tensile strength and elongation of metal rheoformed by die casting are higher by about 37% and 44% respectively than those produced by conventional liquid die casting.     

Preparation of AZ91D Slurries for Semi-Solid Forming Using Al8 ( Mn, Fe) 5 Precipitates

During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.     

半固态铸造技术研究的进展

半固态铸造是一种新的材料成形技术 ,采用半固态铸造技术成形可以实现产品的低成本、高产出及高质量。本文着重介绍了半固态铸造合金的坯料制备和成形方法 ,同时分析了搅拌速度和金属液冷却速度对一次相的影响 ,还对半固态合金微观组织的形成和演化以及充型过程数值模拟等进行了分析 ,提出了发展半固态铸造技术值得重视的问题     

Study on the slurrying and rheological properties of coal–oilfield wastewater–slurry

In this study, oilfield wastewater (OWW) was used to prepare coal–oilfield wastewater–slurry (COWS), and the apparent viscosity, solid concentration, and rheological curve were studied. Compared with original coal–water–slurry (CWS), the maximum solid concentration of COWS increased, and the viscosity decreased; therefore, the slurrying ability of the coal slurry was improved with the use of OWW. However, although the oil in OWW promoted the slurrying ability of the coal slurry, its effectiveness was insufficient, and a chemical additive was still needed to obtain a coal slurry with enhanced slurrying ability. Both COWS and CWS exhibited shear-thinning behavior, and the rheological index value of COWS was lower, which indicated that pseudoplasticity of COWS was more obvious, and OWW improved the rheological properties of coal slurry.     

Microstructure evolution of semi-solid Mg-14Al-0.5Mn alloys during isothermal heat treatment

A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed.And the microstructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed.The results show that the microstructures of cast alloys consist ofα-Mg,β-Mg17Al12 and a small amount of Al-Mn compounds.After holding at 520℃ for 3 min,the phases ofβ-Mg17Al12 and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures ofα-Mg change from developed dendrites to irregular solid particles.With increasing the isothermal time,the amount of liquid increases,and the solid particles grow large and become spherical.When the holding time lasts for 20 min or even longer,the solid and liquid phases achieve a state of dynamic equilibrium.