## 交流磁场对过共晶Al-Fe合金初生相的影响

1. 东北大学理学院 沈阳 110819

2. 东北大学材料电磁过程教育部重点实验室 沈阳 110819

## Effect of Alternating Current Magnetic Field on the Primary Phase of Hypereutectic Al-Fe Alloy

ZHANG Jianfeng1, LAN Qing2, GUO Ruizhen2, LE Qichi,2

1. College of Science, Northeastern University, Shenyang 110819, China

2. Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China

 基金资助: 中国博士后科学基金项目No.  2015M571320以及中央高校基本科研业务费项目No.  N150504002

Corresponding authors: LE Qichi, professor, Tel:(024)83683312, E-mail:qichil@mail.neu.edu.cn

Received: 2018-12-21   Revised: 2019-07-21   Online: 2019-10-29

 Fund supported: China Postdoctoral Science Foundation Funded Project No.  2015M571320and Fundamental Research Funds for the Central Universities.  N150504002

Abstract

The type, morphology and distribution of the Fe-phase in the Al-Fe alloy are some of the key factors affecting the mechanical properties of the Al-Fe alloy. The alternating current (AC) magnetic field can significantly affect the solidification structure of the Al-Fe alloy. However, the mechanism of the Fe-phase in the Al-Fe alloy influenced by the AC magnetic field has not been fully revealed. Therefore, the effect of AC magnetic field on the primary phase of hypereutectic Al-2.55%Fe alloy is studied by means of XRD and OM in this work. The results show that the AC magnetic field cannot change the type of primary phase of the hypereutectic Al-2.55%Fe alloy, which means that the primary phase remains to be Al3Fe phase regardless of the treatment of the AC magnetic field, but the AC magnetic field can obviously influence the distribution and the morphology of the primary Al3Fe phase. Without treatment of AC magnetic field, the primary Al3Fe phase is fine and granular, and uniformly distributed at the bottom of the sample under the effect of gravity. However, under the influence of the AC magnetic field, most of the primary Al3Fe phase is located at the top edge of the sample and is distributed in the shape of a triangle along the radial direction, with only a small part of the fine, granular primary Al3Fe phase distributed in the shape of a pyramid at the bottom of the sample. At the same time, the primary Al3Fe phase morphology in the top of the sample transforms from the original fine particles to large blocks and rods. With the increase of the magnetic induction intensity, the influence of the AC magnetic field on the distribution and morphology of the primary Al3Fe phase grows stronger, and the content of the primary Al3Fe phase in the top of the sample also increases. The influence of AC magnetic field on the primary phase distribution and morphology of the hypereutectic Al-2.55%Fe alloy is the result of the combined action of the Lorentz force and the magnetic force generated by the AC magnetic field.

Keywords： AC magnetic field ; hypereutectic Al-Fe alloy ; solidification structure ; primary phase

Jianfeng ZHANG, Qing LAN, Ruizhen GUO, Qichi LE. Effect of Alternating Current Magnetic Field on the Primary Phase of Hypereutectic Al-Fe Alloy. Acta Metallurgica Sinica[J], 2019, 55(11): 1388-1394 doi:10.11900/0412.1961.2018.00560

Fe是铝合金中常见的一种杂质元素，由于其在Al中的固溶度低，很容易形成粗大针片状含Fe相，从而严重影响合金的力学性能[1]。另一方面，铸造Al-Fe合金中的Al-Fe等金属间化合物又具有高硬度和极好的耐热、耐磨及抗腐蚀性能，在各个工业领域具有广泛的应用前景[2,3]。因此，改变铝合金中的含Fe相的类型、形貌和分布等，是提高Al-Fe合金力学性能的关键。目前，常见的方法有：半固态成型、外加物理场处理、添加合金元素、热处理等[4,5,6,7]。例如：在半固态成型过程，利用流变挤压法可以显著细化Al-Fe合金中的Al3Fe相，从而提高其抗拉强度和延伸率[8]。在传统铸造和半连铸过程中，低频电磁场可以显著细化其铸造微观组织[9]

## 1 实验方法

### 图1

Fig.1   Schematic of the experiment equipment

## 2 实验结果

### 图2

Fig.2   Solidification microstructure of Al-2.55%Fe alloy without alternating current magnetic field (a) and high magnified OM images of zone b (b), zone c (c), zone d (d) and zone e (e) in Fig.2a

### 图3

Fig.3   Solidification microstructure of Al-2.55%Fe alloy with alternating current magnetic field (20 Hz, 300 A) (a) and high magnified OM images of zone b (b), zone c (c), zone d (d) and zone e (e) in Fig.3a

### 图4

Fig.4   Solidification microstructure of Al-2.55%Fe alloy with alternating current magnetic field (20 Hz, 200 A) (a) and high magnified OM images of zone b (b), zone c (c), zone d (d) and zone e (e) in Fig.4a

### 图5

Fig.5   Solidification microstructure of Al-2.55%Fe alloy with alternating current magnetic field (20 Hz, 100 A) (a) and high magnified OM images of zone b (b), zone c (c), zone d (d) and zone e (e) in Fig.5a

### 图6

Fig.6   XRD spectra of the hypereutectic Al-2.55%Fe alloy with (a) and without (b) alternating current magnetic field (20 Hz, 100 A)

## 3 分析讨论

$f=J×B$

$f=1μ0(∇×B)×B=1μ0(B⋅∇)B-12μ0∇B2$

$fro=1μ0(B⋅∇)B$

$fir=-12μ0∇B2$

$B=Bez∂B∂z≠0$

$fro=1μ0(B⋅∇)B=1μ0B∂B∂zez$

### 图7

Fig.7   Schematics of the Lorentz force (B—magnetic induction, $μ0$—permeability of vacuum, $∇$—nabla operator)

(a) rotational force part (fro) (b) non-rotational force part (fir)

$∇(B22μ0)=∇∥(B22μ0)+∇⊥(B22μ0)$

$fir=-∇B22μ0=-∇//(B22μ0)-∇⊥(B22μ0)≠0$

$fir$的方向如图7b所示，在原点之上，沿斜向上方向指向金属内部；在原点之下，沿斜向下方向指向金属内部；在过原点的水平面上，无纵向分量，沿径向指向金属内部。

$B=μ0(H+M)=μ0(1χ+1)M$

## 4 结论

(1) 交流磁场不能改变过共晶Al-2.55%Fe合金初生相的类型，有无交流磁场作用下，初生相均为Al3Fe相。

(2) 交流磁场能显著改变初生Al3Fe相的分布和形貌。无磁场条件下，初生Al3Fe相在重力的作用下均匀地分布在样品的底部，呈细小颗粒状，界面为水平面。而在交流磁场的作用下，除了少部分细小颗粒状的初生Al3Fe相在样品底端中轴线附近呈金字塔状分布外，大部分初生Al3Fe相以块状和棒状出现在样品的顶端边沿处，且沿径向呈三角形分布。

(3) 磁感应强度越大，交流磁场对初生Al3Fe相分布和形貌的影响越大，底部细小颗粒状初生Al3Fe相含量越少，顶部初生Al3Fe相的含量越多，但交流磁场作用效果与磁感应强度之间并非呈线性关系。

(4) 交流磁场对过共晶Al-2.55%Fe合金初生相分布和形貌的影响，主要是由交流磁场产生的Lorentz力和磁力共同作用的结果。

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