一种新型过共晶Al—Si合金变质剂

利用熔铸法（Ｉ／Ｍ）生产出一种过共晶Ａｌ－Ｓｉ合金变质剂，并对其进行了金相显微镜观察和ＳＥＭ观察，试验结果表明，该变质剂在制备过程中直接生成了大量ＡｌＰ化合物，在熔融铝中熔化速度很快，对过共晶Ａｌ－Ｓｉ合金初晶Ｓｉ有良好的变质效果，对Ａｌ－１８％Ｓｉ二元合金而言，Ｐ添加量控制在２０ｐｐｍ～８０ｐｐｍ，初晶硅平均尺寸可减小到２５μｍ～４０μｍ。     

锶在Al—Si—Mg合金中的吸气特性与减耗规律

锶在Ａｌ－Ｓｉ－Ｍｇ合金液中有强烈的吸气性和特殊的减耗过程，在批量生产过程中应特别注意锶的加入方法和加入量。     

锶用于Al—Si合金的变质处理

钠对Ａｌ－Ｓｉ合金共晶硅相变质处理的有效时间短，满足不了现代铸造工艺制度的要求，所以近来采用Ｓｒ变质剂取代钠。本文介绍了Ｓｒ变质处理的发展现状和与Ｓｒ变质处理有关的一些技术问题。     

铝合金Na—Mg变质规律研究

热分析法可以记录试样在冷运过程中的时间－温度曲线。在本文中，根据热分析曲线和大量的试验数据，得到了铝合金Ｎａ－Ｍｇ变质的综合规律，同时也给出了σｂ与ΔＴ之间的数学计算公式。最后把公式计算数据和实验结果做了对比。实践表明：利用本文结论来指导现场生产是一种行之有效的方法。     

Al—Si合金变质效果热分析技术的研究

通过热分析杯的材料，尺寸等系统的试验，确定了一种适合炉前检测铝硅合金变质效果的样杯。结合智能化高精度的测试仪表，研制出炉前铝硅合金变质效果判别的分析装置，并且以牛顿传热平衡方程，合金凝固过程中的平方根定律为理论基础，结合Ａｌ－Ｓｉ合金平衡状态图，推导出铝硅合金变效果的判据－平均固相生长加速度ψＥ。ψＥ的值越小，铝硅合金的变质效果越好。     

Sn对Al-Si-Mg系合金的时效动力学分析

Sn对Al-Si-Mg系合金的时效过程产生明显的影响，合金中加入Sn，若不进行时效处理，Sn作为夹杂降低合金的力学性能，若合金进行时效处理，Sn抑制Mg2Si沉淀相的聚集，长大，使其弥散分布，因而合金的力学性能有较大幅度的提高，运用Pashley时效动力学模型解释了Al-Si-Mg系合金的时效行为，用Lomer公式，通过计算，Al-Si-Mg系合金中加入微量元素Sn后，合金中的过剩空位浓度约为基体中过剩空位浓度的1／200，正是Sn与空位的较高结合能，抑制了Mg2Si沉淀相的粗大。     

Al-Si-Mg合金的晶粒细化工艺及细化机理研究

通过对Al-5Ti-Mg中间合金细化作用的实验研究发现,Al-Si-Mg合金晶粒尺寸明显减小,合金的力学性能提高,尤其是伸长率,并且具有很好的抗衰退能力。细化作用是由于Al3Ti与稳定的TiB2颗粒共存于熔体中,并且Al3Ti在硼化物的{0001}基面上形成稳定的膜。α-Al的生核发生在Al3Ti膜上。σ-Al仅限于在{0001}晶面上生核,表明决定生核效率的主要因素是{0001}晶面的面积。     

SPECIFIC HEAT MEASUREMENTS OF ZrAINiCuCo ALLOY

Specific heats of undercooled liquid, crystal, and glass states for the ZrAlNiCuCo alloy are measured by a calorimeter. Different heating rates are used to enlarge the measuring temperature range of specific heat for an undercooled liquid. The specific heat data of the glass with a zero heating rate are obtained by extrapolating the measured specific heat data of the glass with different heating rates. And specific beat functions of undercooled liquid, crystal and glass are obtained too.     

SPECIFIC HEAT MEASUREMENTS OF ZrAlNiCuCo ALLOY

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Hot deformation behavior of a Sr-modified Al-Si-Mg alloy: Constitutive model and processing maps

Isothermal compression experiments were conducted to study the hot deformation behaviors of a Sr-modified Al-Si-Mg alloy in the temperature range of 300–420 °C and strain rate range of 0.01–10 s^?1. A physically-based model was developed to accurately predict the flow stress. Meanwhile, processing maps were established to optimize hot working parameters. It is found that decreasing the strain rate or increasing the deformation temperature reduces the flow stress. The high activation energy is closely related to the pinning of dislocations from Si-containing dispersoids. Moreover, the deformed grains and the Si-containing dispersoids in the matrix are elongated perpendicular to the compression direction, and incomplete dynamic recrystallization (DRX) is discovered on the elongated boundaries in domain with peak efficiency. The flow instability is mainly attributed to the flow localization, brittle fracture of eutectic Si phase, and formation of adiabatic shear band. The optimum hot working window is 380–420 °C and 0.03–0.28 s^?1.     

Microstructural evolution during unsteady-state horizontal solidification of Al-Si-Mg (356) alloy

The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with the Al-7%Si-0.3%Mg (mass fraction) alloy was carried out. A water-cooled horizontal directional solidification device was developed and used. Microstructural characterization was carried out using traditional techniques of metallography, optical microscopy and SEM microscopy. The Thermo-Calc software was used to generate the solidification path of the investigated alloy with addition of 0.17% Fe (mass fraction). The effects of the thermal parameters such as the growth rate (V_L), cooling rate (T_C) and solidification local time (t_SL) on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition (CET) was found for V_L and T_C values from 0.82 to 0.98 mm/s and from 1.71 to 2.55 °C/s, respectively. The microstructure was characterized by the measurement of the primary and secondary dendrite arm spacings (λ₁ and λ₂, respectively). Experimental laws of λ₁ =f(V_L, T_C) and λ₂ =f(t_SL) were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture: α(Al)+Si+π-Al₈Mg₃FeSi₆+θ-Mg₂Si.     

MODIFICATION EFFECT OF Sr ON Al-Si ALLOYS

By inserting the single crystal silicon seeds into Sr modified Al-22wt-% Si alloy melts,thefact that nucleation and growth of Si-phase are affected by Sr addition has been confirmed.Itis suggested that this effect is caused by the adsorption of Sr on{111}_(si),and the modificationof eutectic structure results from the variation of leading phase in the eutectic from Si to α-Al.     

MECHANISMS AND PREDICTION OF FRACTURE TOUGHNESS ANISOTROPY OF HIGH STRENGTH Al ALLOYS

Contributions of weak grain boundary,cracking path deflection and grain boundarydelamination to fracture toughness anisotropy of high strength Al alloys were evaluated basedupon approaches of fracture mechanics in conjunction with physical cracking mechanisms.The predicted results are close to those experimentally determined in the literature and in thiswork.The strong anisotropy of fracture toughness of high strength Al alloys is therefore attri-buted mainly to weak grain boundary cracking,cracking path deflection and grain boundarydetamination.With the methods of this work,short-transverse fracture toughness values ofsome semi-products can he estimated from in-plane toughness values and corresponding frac-ture characteristics when it is difficult to be determined experimentally.     

亚共晶Al-Si合金变质级别的定量金相分析

采用图像分析技术,通过分析亚共晶Al-Si合金共晶硅相几何参数与变质级别的关系,建立了变质级别的量化指标,实现了亚共晶Al-Si合金变质级别的定量金相分析,分析表明,共晶硅相的形状因子反映了AFS变质级别的变化趋势,综合考虑共晶硅相形状及大小给出的面积加权形状因子与变质级别之间有很好的对应关系,可用来准确表征亚共晶Al-Si合金的变质级别。     

THERMAL CONDUCTIVITY OF Al-Li ALLOY AT CRYOGENIC TEMPERATURES

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