简介概要

Nanostructured Al-Zn-Mg-Cu alloy synthesized by cryomilling andspark plasma sintering

来源期刊:中国有色金属学报(英文版)2009年第5期

论文作者:陈汉宾 陶凯 杨滨 张济山

文章页码:1110 - 1115

Key words:cryomilling; spark plasma sintering; nanostructured Al-Zn-Mg-Cu alloy; microstructural evolution; second phase

Abstract: Nanocrystallized Al-10.0%Zn-3.0%Mg-1.8%Cu (mass fraction) alloy powder was prepared by cryomilling, and then the nanostructured powder was consolidated into bulk material by spark plasma sintering (SPS). The microstructural evolution and phase transformation were studied. A supersaturated face-centered cubic solid solution is formed after cryomilling for 10 h, and the average grain size is 28 nm. Two typical nanostructures of the bulk nanostructured alloy are observed:primarily equiaxed grains with size of 150 nm, and occasionally occurring sub-micron grains up to 500 nm. Two types of MgZn2 particles precipitate during consolidation. One is the sub-micron particles distributed along the boundaries of the powders, and the other is fine particles with size of several nanometers in the matrix, especially at the boundaries of sub-micron grains. These second phase particles can be completely dissolved into matrix by proper solid solution treatment.

基金信息:the Hi-tech Research and Development Program of China
the Research Fund for the Doctoral Program of Higher Education, China



详情信息展示

Nanostructured Al-Zn-Mg-Cu alloy synthesized by cryomilling and spark plasma sintering

CHEN Han-bin(陈汉宾)1, TAO Kai(陶 凯)2, YANG Bin(杨 滨)2, ZHANG Ji-shan(张济山)2

1. No.59 Institute of China Ordnance Industry, Chongqing 400039, China;

2. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing,

Beijing 100083, China

Received 23 September 2008; accepted 17 January 2009

                                                                                                 

Abstract: Nanocrystallized Al-10.0%Zn-3.0%Mg-1.8%Cu (mass fraction) alloy powder was prepared by cryomilling, and then the nanostructured powder was consolidated into bulk material by spark plasma sintering (SPS). The microstructural evolution and phase transformation were studied. A supersaturated face-centered cubic solid solution is formed after cryomilling for 10 h, and the average grain size is 28 nm. Two typical nanostructures of the bulk nanostructured alloy are observed: primarily equiaxed grains with size of 150 nm, and occasionally occurring sub-micron grains up to 500 nm. Two types of MgZn2 particles precipitate during consolidation. One is the sub-micron particles distributed along the boundaries of the powders, and the other is fine particles with size of several nanometers in the matrix, especially at the boundaries of sub-micron grains. These second phase particles can be completely dissolved into matrix by proper solid solution treatment.

Key words: cryomilling; spark plasma sintering; nanostructured Al-Zn-Mg-Cu alloy; microstructural evolution; second phase

                                                                                                

1 Introduction

Precipitation-strengthened 7xxx series Al alloys are well applied in aeronautical field due to their excellent mechanical properties[1], which are greatly influenced by the morphology and distribution of precipitates. Usually, optimizing heat treatment[2-4], increasing the content of major alloying elements[5-6], and reducing grain size[7-8] are employed to enhance the mechanical properties of these alloys. Thereby, techniques such as spray-forming[6-7] and powder metallurgy[8-9] are widely used. However, the grain size of materials obtained from these techniques is in the range of micro-scale. The potential for enhancing the mechanical properties of structural materials by reducing grain size to nanosize has attracted considerable interests in recent years. Thus, preparation of these aluminum alloys with nanocrystallines is worthy to pay attention.

Now, mechanical alloying is the main approach to fabricate nanocrystalline metal and alloy powders. However, some difficulties arise during ball milling ductile metals and their alloys due to the relatively stronger tendency of powder particles to adhere to container walls and sinter to form large millimeter-sized particles, which arise from re-welding conducted by localized high temperature. The introduction of cryogenic liquid media during milling, namely cryomilling, can effectively solve this problem[10]. Recently, cryomilling has been noted to produce nanocrystalline aluminum and its alloy powders[10-14]. And hot/cold isostatic pressing and extrusion are usually employed to consolidate these nanocrystalline powders to bulk nanostructured materials[15-20]. However, prohibiting rapid grain growth during conventional consolidations is still a challenge. The previous investigations demonstrated that the average grain size was normally increased by 130%-250% during extrusion following hot isostatic pressing process as extrusion changed the arrangement of the dispersions that pinned the grain boundaries[18]. Furthermore, the milled or cryomilled multi-phase nanocrystalline alloy powders with a high content of alloying elements are all in the state of supersaturated solid solution. Precipitation occurs when these powders are subjected to thermal consolidation. The velocity of the precipitates is higher than that of the coarse crystal counterparts due to the high energy and the shorter diffusion path in nanocrystalline materials. In the conventional thermal consolidation process, the precipitates coarsen excessively owing to the relative higher temperature and long time. These coarse precipitates reduce the mechanical properties and increase the difficulty in heat treatments. Spark plasma sintering(SPS) is a novel technique for rapidly sintering powders. It can fabricate bulk nanostructured materials with a relatively low temperature and very short time[21-22]. Surface activation of powder particles in SPS is conducted by pulsed current, which contributes to the powders densification.

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