Elsevier

Materials & Design

Volume 99, 5 June 2016, Pages 303-313
Materials & Design

Preparation, thermal analysis and mechanical properties of in-situ Al2O3/SiO2(p)/Al composites fabricated by using zircon tailing sand

https://doi.org/10.1016/j.matdes.2016.03.064Get rights and content

Highlights

  • Zircon tailing sand was used for fabricating the Al2O3/SiO2(p)/Al composites.

  • The SiO2/Al in-situ reaction has taken place in molten Al.

  • Suitable process parameters were carried out to uniformly disperse the zircon sand in Al melts.

  • Mechanical properties are increased by the addition of zircon tailing sand.

Abstract

Zircon tailing sand (comprised of SiO2 and Al2SiO5) was utilized as reinforcement precursors to prepare aluminum matrix composites (AMCs) by using indigenously developed stir casting technique. The Al2O3/SiO2(p)/Al composites were successfully fabricated at different vol.% (viz. 1.1, 3.2, 5.4, 7.5 and 9.7) of zircon tailing sand and their metallurgical and mechanical properties have been analysis. The SiO2/Al reaction in molten composites was proven by using the cooling curve thermal analysis (CCTA). Particles dispersion and wettability at SiO2/Al interface were improved with the optimized process parameters (i.e., particles preheating at 700 °C × 1 h, feeding rate at 10 g/min and stirring time for 10 min). Optical and SEM micrographs revealed the uniform distribution of reinforcements in the matrix. X-ray diffraction patterns and EDS testing results of the prepared AMCs revealed the presence of Al2SiO5, Al2O3, Si and the special duplex phase. The Brinell hardness, ultimate tensile strength and yield strength (σ0.2%) of the composite were improved with the addition of zircon tailing sand in Al matrix. Fractured surface was carried out to explain the % elongation reduction and failure mechanism of these composites.

Introduction

Engineering interest in the aluminum matrix composites (AMCs) has increased [1], owing to their high specific strength, high hardness, and high toughness. The application potential of AMCs [2] mainly depends on the preparation process [3], microstructure [4] and properties of the reinforcements [5]. Many methods, such as squeeze casting [6], powder metallurgy [7], stir casting [8], and spray deposition [9], have been developed for fabricating particle reinforced AMCs. Among them, stir casting is widely used to prepare ceramic particles reinforced AMCs. By using this technique, the ceramic particles (e.g. SiC(p) and Al2O3(p) etc.) whose wettability are poor can be easily mixed into the molten Al at a relatively low temperature [10], [11]. Traditional researches on stir casting process [12], [13], [14] indicated that the dispersion of the reinforcements in molten Al mainly depended on the rotation speed, temperature of the melts and the shape of the stirrer. In order to uniformly disperse the particles and promote their mechanical properties, researchers have paid their attention on the wettability at ceramic/Al interface. Geng et al. [15] improved the wettability of discontinuous reinforcement in molten Al by preheating the reinforcement. Chen et al. [16] studied the dispersion and wettability of TiB2 in Al melts at different stirring time. A special feeder made particles effectively immerse into the melts was designed by Tony Thomas et al. [17].

According to the published reports [18], [19], [20], the mechanical properties of the AMCs could be promoted by incorporating the ceramic particles with high hardness (e.g. SiC(p), Al2O3(p), and Al2SiO5 etc.). The SiO2 particles are also favorable to AMCs fabrication. Without adding any alloying addition, the contact angle at the Al/SiO2 interface below 1000 °C is 70°–90° [21]. It indicates that SiO2 particles can be spontaneously wet by molten Al.

The source of SiO2 is abundantly available. An attempt has been made to prepare AMCs reinforced with glass waste (SiO2) [22]. Moreover, several researchers [1], [23] reported the AMCs with high strength by using the fly ash particles (with 49.5% SiO2 [1]) from a power plant. In this study, the reinforcement precursor (mainly comprises of SiO2 and Al2SiO5) was collected from the alloy manufacturers who supplied Zr to the nuclear reactors and aerospace industry. The abundant but useless zircon tailing sand was dumped in designated landfills. It has led to a series of considerable environmental problems. Utilizing the zircon tailing sand in AMCs industry is good for the cost reduction. Also, it is helpful to solid waste treatment.

To the best of our knowledge, there has been no synthesis of AMCs using the zircon tailing sand, till date. In order to know the strengthening effect of zircon tailing sand and the products from SiO2/Al in-situ reaction, pure Al was selected as the composite matrix. The wettability and dispersion of the particles in molten Al were improved by using the proper stir casting parameters. The cooling curve thermal analysis (CCTA) [24] was carried out to prove the in-situ reaction in molten Al.

Section snippets

Raw materials for AMCs preparation

The reinforcement precursor, zircon tailing sand, was obtained from the landfills of a Zr alloy manufacturer. The density of zircon tailing sand was about 2.5 g/cm3. The XRD pattern and chemical composition of the as-received zircon tailing sand are shown in Fig. 1. Table 1 shows the chemical composition of the pure Al matrix (commercial pure Al with purity of 99.9 wt.% and density of 2.7 g/cm3).

Fig. 2a shows the morphology of the zircon tailing sand. The main compositions of these particles are

SiO2/Al reaction in Al melts

Fig. 6a and b show the cooling curves and their first and second derivative of Sample-1 and Sample-6, respectively. The baselines used for evaluating the fraction solid curves are given in these two diagrams. The cooling rates of these melts are about 0.5 ± 0.1 °C/s (calculated from the slope of the cooling curves before liquidus temperature). Fig. 6c and d show the magnified images of area A and B marked in Fig. 6a and b. The onset temperature of the nucleate point (TN) was determined by using

Conclusions

The conclusions derived from this research are given below:

  • 1)

    The uniform dispersion of zircon tailing sand with better wettability in pure Al matrix was obtained by using particles preheating at 700 °C × 1 h, feeding rate at 10 g/min and stirring time for 10 min.

  • 2)

    Few pores and particle agglomerates could be found in the fabricated AMCs containing 5.4 vol.% and 7.5 vol.% of zircon tailing sand.

  • 3)

    The SiO2/Al in-situ reaction has taken place in molten Al during fabricate process.

  • 4)

    The UTS of Al2O3/SiO2(p)/Al

Acknowledgments

The authors gratefully acknowledge the support of the Science and Technology plan projects with Grant No. 2013B090500091 of Guangdong Province, China. The raw materials used in this study were acquired as a courtesy from Guangzhou Kinbon non-ferrous alloy metals Co. Ltd.

References (35)

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