Elsevier

Journal of Alloys and Compounds

Volume 540, 5 November 2012, Pages 100-106
Journal of Alloys and Compounds

Effect of mechanical alloying on the microstructure and properties of Al–Sn–Mg alloy

https://doi.org/10.1016/j.jallcom.2012.04.098Get rights and content

Abstract

Aluminum–tin–magnesium alloys have emerged as one of the most effective alloying compositions for enhanced sinterability. However, to-date the effect of mechanical modification of powders on the phase development, sintering and properties of these alloys has not been the subject of appropriate scientific attention. The present paper therefore discusses the influence of mechanical alloying of Al–8Sn–5Mg elemental powders on the microstructure and properties of the sintered product. Sintered mechanically alloyed products were found to be harder and denser than sintered products using un-milled powder. The initial green density was also found to play a significant role in the phase content of the sintered products made from mechanically alloyed powder.

Highlights

► Effect of mechanical activation on sintering and properties of Al–Sn–Mg alloys were studied. ► Mechanical activation increases hardness and density of the sintered products. ► Green density affects relative amounts of phases following sintering of mechanically activated powder. ► High green density results in higher final sintered density and hardness.

Introduction

Aluminum (Al) alloys represent a cornerstone of engineering materials that has monopolized many industrial applications. The production of these materials through powder metallurgy approaches provides many advantages in terms of net shape processing, no material waste and microstructural control [1], [2]. The presence of an aluminum oxide layer on the surface of aluminum powder had been for some time a major obstacle to its sintering [3], [4]. A number of studies have focused on overcoming this problem, through control of powder alloy composition and environment [5], [6], aluminum powder shape [7] or mechanical breakup of the oxide on aluminum powder for example through processes such as mechanical milling [8], [9]. One of the alloy compositions that have been proven effective for sintering involves the addition of tin (Sn) and magnesium (Mg) to aluminum [10]. On the other hand, mechanical alloying is a process that can subject elemental powders to mechanically-induced modifications which can in turn activate powders thus promoting enhanced sintering characteristics and result in products with unique microstructures and properties [11], [12]. However, the mechanical alloying of Al–Sn–Mg alloys has not so far received appropriate attention as a viable powder processing/modification route prior to sintering. The present paper discusses the effect of mechanical alloying and green density on the microstructure, phase content, and micro-hardness of sintered Al–8Sn–5Mg alloys.

Section snippets

Experimental procedures

Fig. 1 shows the elemental powders used in the experiments which were Al (1–5 μm , Atlantic Equipment Engineers, USA) ,Sn (1–5 μm , Atlantic Equipment Engineers, USA) and Mg (-325 mesh, Alfa Aesar, USA). Paraffin wax (McMaster Carr, USA) was used as the binder and n-heptane (Alfa Aesar, USA) was used as the solvent. Two different mixing procedures were investigated. The first involves rotator mixing the elemental powders in the composition Al-8 wt.% Sn-5 wt.% Mg at 70 rpm for 30 min. Powder produced

Results and discussion

The effect of mechanical alloying time on the particle size evolution is shown in Fig. 2. It can be seen that after 3 min, elemental powders are still not well dispersed throughout the batch. However, at and above 30 min of milling, powders appear well mixed and particle size is seen to initially increase followed by a decrease, which is a generally observed characteristic of the mechanical alloying process [9] due to the interplay between particle welding and particle fracture.

The 300 min milling

Conclusions

A number of conclusions can be drawn from the present work:

  • 1.

    Mechanical alloying under the current investigated conditions gives rise to first the formation of cubic Mg2Sn during mechanical alloying, and then a metastable hexagonal Mg2Sn during sintering.

  • 2.

    Mechanical alloying results in a significant increase in hardness and density of the sintered products compared to un-milled powder.

  • 3.

    For mechanically alloyed powder, green density has a significant effect on the relative amounts of phases produced

Acknowledgments

The authors wish to thank the National Science Foundation for their support (major research instrumentation (MRI), DBI-0959908), and Dr. Steve Barlow, and Ms. Joan Kimbrough for their assistance with SEM and XRD work respectively.

References (13)

There are more references available in the full text version of this article.

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