Rapid communicationInfluence of SiC particles on compressive deformation of magnesium matrix composites
Highlights
► Compression behaviour in magnesium matrix composites using synchrotron radiation diffraction. ► Plasticity is controlled by the tensile twining system. ► The volume fraction of twins rapidly saturates as the volume fraction of reinforcement increases. ► SiC particles balance the tensile stress generated by twin formation.
Introduction
A basic study of plastic deformation in extruded magnesium matrix composites is complicated since magnesium alloys develop a strong texture with the basal plane perpendicular to the deformation direction during thermomechanical processing. The strong influence of the crystallographic texture on the plastic deformation of magnesium alloys and magnesium matrix composites makes it difficult to isolate and evaluate the role of the reinforcing mechanism in the strength of the composites. Recently, the evolution of internal elastic strains during in situ tensile tests of an extruded AZ31 alloy reinforced with SiC particles has been measured using Synchrotron Radiation Diffraction (SRD) [1]. This technique allows the elastic strain and stress of each phase to be measured separately. The plasticity of the AZ31 alloy reinforced with stiff ceramic particles behaves similarly to the unreinforced alloy, i.e. it is controlled by the crystallographic texture of the matrix. However, the SiC particles clearly bear the load transferred by the magnesium matrix.
Following on from this research, the present paper explores the deformation mechanism during compression in an extruded AZ31 alloy reinforced with SiC particles. Since AZ31-SiC composites develop a fibre texture with the basal plane parallel to the extrusion direction [1], the activation of tensile twinning is expected during compression testing in the extrusion direction [2], [3], [4], thus allowing the influence of ceramic particles on deformation by twinning to be evaluated. The plastic deformation of Mg-alloys and the role of twinning have been thoroughly investigated in the last years [5], [6], [7], [8], [9], [10]. However, the influence of the presence of ceramic particles on the deformation by twinning is not completely clear. The evolution of internal strain has been measured by SRD during in situ compression tests of the unreinforced and reinforced AZ31 alloy. These values have been compared with those obtained during in situ tensile tests.
Section snippets
Experimental procedure
AZ31 powders of less than 100 μm in size were blended with 5 and 10 vol.% 6 μm SiC particles. Blend homogenisation was conducted in a Turbula® shaker-Mixer for 10 h. After homogenisation, the powders were uniaxially cold compacted up to 310 MPa. Compacts of 40 mm in diameter were extruded at 350 °C employing an extrusion ratio of 18:1. For comparison, the original AZ31 powders were also extruded in the same conditions.
The microstructure of the composites was characterised by a homogenous distribution
Results and discussion
Fig. 1 shows the compressive tests for the AZ31 alloy and both composites. Tensile tests are also presented for comparison [1]. The stress–strain curves are similar for all the materials. The AZ31 alloy shows elastic behaviour up to 200 MPa. After yielding, the stress is approximately constant for around 2% of the strain, after which both the stress and the work hardening increase again. For composites, the yield stress and work hardening increase with the higher volume fraction of SiC
Conclusions
The influence of the presence of ceramic particles on the twinning mechanism in magnesium matrix composites has been measured using synchrotron radiation diffraction during in situ compressive tests. The following conclusions may be drawn from this study:
- (a)
The plasticity of extruded AZ31 alloy reinforced with stiff ceramic particles behaves similarly to the unreinforced alloy, i.e. it is controlled by the twinning process. However, the volume fraction of twins decreases as the volume fraction of
Acknowledgements
Magnesium Elektron is kindly acknowledged for supplying the AZ31 cast alloy. BESSY (Berlin, Germany) is kindly acknowledged for beamtime on the beamline EDDI. We kindly acknowledge the support of the EU during the measurements at BESSY. G.G. gratefully acknowledges the support of the INTRAMURAL-Project. Elvira Oñorbe thanks the CSIC for a JAE fellowship.
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