H.C. Liao M. Zhang J.J. Bi K. Ding X. Xi S.Q. Wu
材料科学技术（英文）
Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization. In unmodified alloy, dual eutectic structure has been observed. The coarse eutectic (dendrite-like Al+ coarse Si flakes) is formed above the equilibrium temperature of eutectic (Al+Si) reaction (577°C). The coarse eutectic (CE) grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes. The fine eutectic (FE) grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes. The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles. Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE. This is because the eutectic point has moved far enough to make the alloy, at this composition (Al-13 wt pct Si), hypo-eutectic. Local cooling rate during solidification has an important influence on competition formation of these two eutectics.
关键词:
Al-Si alloy
,
eutectic
,
solidification
,
dual eutectic grains
,
grain refinement
杨振国
,
杜维玺
,
杜森林
,
刘素兰
金属学报
本文用阳极溶解计时电位法,对稀土金属La在液态Al-Si合金中的扩散系数进行了测定。结果表明,973K,La浓度18.0×10~(-4)mol·cm~(-3)时,La在Al-5.2wt-％Si合金液中的扩散系数平均值DLa(Al-SI)=(0.91±0.01)×10~(-5)cm~2·S~(-1)。在953-1053K温度范围内,求得La在合金液中的扩散系数与温度间存在下列关系: lgDLa(Al-SI)=-1.78×10~(-3)-4909/T同时求得扩散激活能Q=94.00kJ·mol~(-1)。为了便于分析比较,对Sr在某些条件下的扩散系数也进行了测试。通过La,Sr扩散数据的比较,分析了变质元素的扩散对变质过程中出现的潜伏期,临界冷却速度等问题的影响。
关键词:
扩散系数
,
activation energy
,
La
,
Al-Si alloy
徐达鸣
,
李庆春
,
王永前
金属学报
应用定向凝固/重熔技术研究了Al-Cu,Al-Ni和Al-Si合金定向生长共晶组织的熔化行为实验结果表明:共晶组织的熔化过程与其凝固生长过程之间不存在完全的互逆性无论是规则片状或棒状共晶组织,或是不规则片状共晶组织,其熔化过程都是共晶组织的两相首先在熔化界面上同时分解,形成各自的分散相,然后这些成分不同的分散相经过进一步溶解混合才形成成分均匀的单一液相
关键词:
熔化行为
,
eutectic structure
,
Al-Cu alloy
,
Al-Ni alloy
,
Al-Si alloy
郄喜望
,
李捷
,
马晓东
,
张忠涛
,
李廷举
金属学报
在不同的恒温条件下,对Al-Si合金熔体进行不同时间的超声处理, 当超声处理时间为60 s时, 试样含气量显著降低, 除气效果明显. 在Al--Si合金凝固过程中施加超声场,晶粒发生球化、细化现象; 在Al-Si合金凝固区间恒温条件下施加超声场, 晶粒发生细化但未发生球化现象. 超声场作用下Al-Si合金晶粒细化主要是由于空化泡破碎产生的过冷生核所造成的.
关键词:
超声场
,
Al-Si alloy
,
degassing effect
,
grain refinement
葛丽丽
,
刘日平
,
王强
,
王文魁
金属学报
利用电磁悬浮设备, 通过在真空状态下反复加热与冷却处理, 获得了Al50Si50 (原子分数)合金熔体的深过冷,
最大过冷度为320 K. 观察了不同过冷度下凝固样品小球的表面及其截面
深腐蚀后的组织形貌. 过冷度较小时, 初生相Si为板条状枝晶形貌, 并在其中发现了Al的
层状沉积；过冷度较大时, 初生相Si转变为粒状形貌. 共晶体的形貌也随过冷度的增大转变
为离异共晶形态. 较大过冷度下, 微观组织中发现有晶粒细化现象, 这与Si晶体生长受溶质
的抑制及初生相Si枝晶的断裂有关.
关键词:
过冷凝固
,
Al-Si alloy
Hengcheng LIAO
,
Guoxiong SUN
材料科学技术（英文）
Optical microscope and scanning electron microscope were used to observe the microstructure of the Al-11.6%Si and Al-11.6%Si-0.4%Mg alloys and the morphology of the massive silicon particles. It is found that the massive silicon phase, observed in the unfully modified alloys with 0.010%Sr, disappears completely in the alloys fully modified with 0.020%Sr. The serrations and reentrant edges shown in the massive silicon particles with the conventional casting indicate that the TPRE mechanism plays an important role in the growth of the massive silicon phase. The ripples and steps suggest that the "lateral microscopic growth" may be another operating mechanism.
关键词:
Al-Si alloy
,
null
,
null
,
null
LIU Qiyang LI Qingchun ZHANG Jiren Harbin Institute of Technology
,
Harbin
,
China LIU Qiyang
,
Division of Foundry
,
Department of Mechanical Engineering No.2
,
South China University of Technology
,
Guangzhou
,
China
金属学报(英文版)
By inserting the single crystal silicon seeds into Sr modified Al-22wt-% Si alloy melts,the fact that nucleation and growth of Si-phase are affected by Sr addition has been confirmed.It is suggested that this effect is caused by the adsorption of Sr on{111}_(si),and the modification of eutectic structure results from the variation of leading phase in the eutectic from Si to α-Al.
关键词:
Al-Si alloy
,
null
,
null
GUI Manchang
,
JIA Jun
,
SONG Guangchun
,
LI Peiyong
,
LI QingchunHarbin Institute of Technology
,
Harbin
,
China
金属学报(英文版)
In the light of DSC, electronic microprobe and X-ray diffration analyses of the melt-spinning ribbons and the structures of liquid hypoeutectic Al-7%Si, euteclic Al-12.7%Si and hypereutectic A1-18%Si alloys have been investigated. The results show that the Al-Si clusters in liquid hypoeutectic Al-Si alloy, the Si-Si clusters in liquid eutectic and hypereutectic Al-Si alloys exist at low temperatures, however, the size of clusters decreases gradurally with increasing temperature. This process in which inhomogeneous liquid turns into homogeneous one happens in a range of temperatures.
关键词:
Al-Si alloy
,
null
,
null
Yutuo ZHANG
,
Chengzhi WANG
,
Dianzhong LI
,
Yiyi LI
金属学报(英文版)
doi:10.1016/S1006-7191(08)60089-7
Single dendrite and multi-dendrite growth for Al-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking phenomenon can be observed. For multi-dendrite growth, there exists the competitive growth among the dendrites during solidification. As solidification proceeds, growing and coarsening of the primary arms occurs, together with the branching and coarsening of the secondary arms. When the diffusion fields of dendrite tips come into contact with those of the branches growing from the neighboring dendrites, the dendrites stop growing and being to ripen and thicken.
关键词:
Phase field modeling
,
null
,
null
,
null
