Deformation behaviour of an AS21 alloy reinforced by short Saffil fibres and SiC particles

https://doi.org/10.1016/j.jmatprotec.2005.02.188Get rights and content

Abstract

The high temperature behaviour of composites with the AS21 magnesium alloy matrix reinforced with short Saffil fibres and SiC particles were investigated in the temperature range from room temperature to 300 °C. The yield stress and the maximum stress decrease with increasing temperature. Two types of specimens were investigated – one with fibres plane oriented parallel to the stress axis and the other with perpendicular fibres plane orientation. Light and scanning electron microscopy were used for study of the microstructure of composites. Possible hardening and softening mechanisms are discussed. The shear stress at reinforcing phase/matrix interfaces was of greatest importance in this regard, though the contribution resulting from the dislocation density increase was also significant.

Introduction

Light alloys reinforced with short fibres or particles allow adapting more exactly the work piece material properties to requirements. There is an increasing trend in the automotive industry to use these materials for various parts. Advanced properties of metal matrix composites are [1]:

  • increased apparent limit of elasticity, stiffness, tensile and fatigue strength;

  • improved creep resistance and high temperature properties;

  • improved material damping;

  • increased wear resistance;

  • decreased thermal expansion.

Investigations of mechanical and physical properties of light metals composites (among them magnesium alloys based composites) is important not only for applications but also for better understanding of the processes responsible for their behaviour. The objectives of the present paper are to study the deformation behaviour of the AS21 alloy based composite and hybrid composite and to discuss possible contribution of Saffil ceramic fibres and SiC particles to strengthening as well as softening of these materials.

Section snippets

Experimental procedure

Commercial AS21 (2.2 wt% Al–1 wt% Si–0.1 wt% Mn–balance Mg) alloy was used as the matrix material. Composites with 30 vol.% short fibres of δ-Al2O3 (Saffil®) (hereafter AS21(f)) and hybrid composites with 5 vol.% of Saffil short fibres and 15 vol.% of SiC particles (AS21(f + p)) were used in this study. Composites were prepared by squeeze casting technique. The preforms consisted of planar randomly distributed Saffil fibres as well as Saffil fibres with equiaxial SiC particles. The microstructure of

Experimental results

Fig. 3 shows the true stress–true strain curves obtained for AS21(f) composite with the fibres plane parallel to the stress axis, deformed at various temperatures. Samples were deformed either to fracture or at higher temperatures to predetermined strains.

The temperature dependences of the characteristic stresses, the yield stress σ02 as well as the maximum stress σmax, for the composite with the fibres plane parallel to the stress axis () are shown in Fig. 4. The curves (Fig. 3, Fig. 4)

Discussion

Both composites are inhomogeneous in both elastic as well as plastic properties. While the reinforcing phase remains usually only elastic deformed due to mechanical loading of composites, the plastic deformation occurs in the matrix. Trojanová et al. [7] discussed various strengthening mechanisms in Mg alloys based composites. The most important contributions were found to be the load transfer from the matrix to the fibres and the influence of the increased dislocation density arising from

Conclusions

Ceramics fibres and particles influence significantly mechanical properties of composites with the AS21 matrix. Contribution of short fibres to strengthening of the composite is higher than particles. Perpendicular orientation of the planes, in which fibres are randomly distributed, has a weaker influence on the composite deformation properties. Paralell orientation of the fibres plane in composites markedly increases characteristic stresses. This fibres impact decreases with increasing

Acknowledgements

This investigation was financially supported by the Grant Agency of the Academy of Sciences of the Czech Republic (grant no. A2041203) and the Grant Agency of the Czech Republic (grant no. 106/03/0901).

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