简介概要

Aluminum matrix composites reinforced by in situ Al2O3 and Al3Zr particles fabricated via magnetochemistry reaction

来源期刊:中国有色金属学报(英文版)2010年第11期

论文作者:赵玉涛 张松利 陈刚

文章页码:2129 - 2133

Key words:aluminum matrix composites; magnetochemistry reaction; Al2O3; Al3Zr; in situ tensile

Abstract: Aluminum matrix composites reinforced by in situ Al2O3 and Al3Zr particles are fabricated from A356-Zr(CO3)2 system via magnetochemistry reaction, and the morphologies, sizes and distributions of the in situ particles as well as the microstructures, mechanical mechanisms of the composites are investigated by XRD, SEM, TEM and in situ tensile tests. The results indicate that with the pulsed magnetic field assistance, the morphologies of the in situ particles are mainly with ball-shape, the sizes are in nanometer scale and the distributions in the matrix are uniform. The interfaces between the in situ particles and the aluminum matrix are net and no interfacial outgrowth is observed. These are due to the strong vibration induced by the applied magnetic field in the aluminum melt, which in turn, accelerates the melt reactions. The effects of the magnetic field on the above contributions are discussed in detail.



详情信息展示

Aluminum matrix composites reinforced by in situ Al2O3 and Al3Zr particles fabricated via magnetochemistry reaction

ZHAO Yu-tao(赵玉涛), ZHANG Song-li(张松利), CHEN Gang(陈 刚)

School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China

Received 23 October 2009; accepted 16 September 2010

Abstract: Aluminum matrix composites reinforced by in situ Al2O3 and Al3Zr particles are fabricated from A356-Zr(CO3)2 system via magnetochemistry reaction, and the morphologies, sizes and distributions of the in situ particles as well as the microstructures, mechanical mechanisms of the composites are investigated by XRD, SEM, TEM and in situ tensile tests. The results indicate that with the pulsed magnetic field assistance, the morphologies of the in situ particles are mainly with ball-shape, the sizes are in nanometer scale and the distributions in the matrix are uniform. The interfaces between the in situ particles and the aluminum matrix are net and no interfacial outgrowth is observed. These are due to the strong vibration induced by the applied magnetic field in the aluminum melt, which in turn, accelerates the melt reactions. The effects of the magnetic field on the above contributions are discussed in detail.

Key words: aluminum matrix composites; magnetochemistry reaction; Al2O3; Al3Zr; in situ tensile

1 Introduction

Particle-reinforcement aluminum metal matrix composites (PRAMMCs) are attractive for the materials scientists to meet the increasing demands of applying advanced structures in aerospace, military, automobile and electronic areas because of their low density, high specific stiffness, strong wear resistance, reduced thermal expansion coefficient and high thermal conductivity, such as aerofoil, motor cylinder body, braking pan[1-5]. PRAMMCs can be fabricated by ex-situ synthesis (e.g. liquid ingot casting and powder metallurgy) where particles are added to the melt as a powder, and also by in-situ synthesis (e.g. exothermic dispersion, reactive hot pressing, reactive infiltration and direct melt reaction) where particles are synthesized within the melt[6-12]. In ex-situ methods, the particles are added into the metal melt from the outside, which induces interface pollution, poor wetting ability and weak properties of the composites. In in-situ process, the reinforcement phases are formed in the matrix metal from chemical reactions or from exothermic reactions between elemental powders of the composite under hot pressing conditions, which are thermodynamically stable, free of surface contamination and disperse more uniformly, leading to stronger particle-matrix bonding. Such unique properties make the in-situ PRAMMCs possess excellent mechanical properties and economical viability than their ex-situ counterparts. In particular, the direct melt reaction (DMR) process is the most promising in-situ synthesis techniques for commercial applications due to its simplicity, low cost and near net-shape forming capability. In the conventional DMR processing, long agitating time at high temperature is necessary for obtaining full incorporation and thorough reaction of the added reactants with the molten metal. These lead to the in situ particles growing up or agglomerating together and more melt being lost, and induce the properties decreasing. In order to shorten the long mixing time at high temperature, some researches have been done[13-15].

In the present work, the aluminum matrix composites reinforced by Al2O3 and Al3Zr particles are fabricated from an A356-Zr(CO3)2 system through magnetochemistry reaction, and the morphologies, sizes and distributions of the in situ particles as well as the microstructures, mechanical mechanisms of the composites are investigated by XRD, SEM, TEM and in-situ tensile observations. The effects of the magnetic field on the above contributions are discussed in detail.

2 Experimental

The starting materials were commercial A356 alloy ingots and inorganic salt Zr(CO3)2 powder.

Firstly, Zr(CO3)2 powders were dehydrated at 250 °C for 3 h in an electric furnace. Then aluminum ingots were heated to 900 °C and melted, the dried Zr(CO3)2 powders with the mass fraction of 20% to the total aluminum melt were added and pressed into the aluminum melt with a campanulate graphite mantle. During the in situ reaction, the impulse magnetic field system (WY1600) was turned on and the frequency was fixed at 25 Hz and the magnetic current intensity was 150 A. The parameters of pulsed magnetic field were voltage 550 V, current 10 A, frequency 100 kHz and pulse width 10 ms. After 20 min, the melt was degassed by hexachloroethane degasifying agent, deslagged, and then poured into a mould with 14 mm inner diameter. After being cooled to room temperature in air, the specimens for XRD, SEM and TEM analyses, mechanical properties testing and in situ tension test were processed. The tensile properties are the average values of three tests.

SEM(JOEL-JXA-840) with a microtensile holder was used to investigate the microstructure of the as- prepared specimens and the in-situ tensile test, and TEM(JSM2010) for the morphologies and the interfaces. Tensile properties tests of the specimens with a gauge diameter of 6.35 mm and length of 25.4 mm were carried out at room temperature by a computer-controlled electronic tensile testing machine (DWD-200) at a strain rate of 1.67×10-4 s-1 according to the ASTM E8 standard. The Brinell Hardness was determined by THI100 electronic-controller type hardness testing device according to the ASTM E10 standard. The values of the tensile properties and Brinell hardness are the average of three tests at each condition, respectively.

3 Results and discussion

3.1 XRD pattern

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