Wear assessment of composite surface layers in Al–6Mg alloy reinforced with AlCuFe quasicrystalline particles: Effects of particle size, microstructure and hardness

Abstract

Aluminium alloys reinforced with ceramic, intermetallic or quasicrystalline particles can fill the needs of automotive and aerospace industries due to their superior properties. In this paper, near-surface layers in Al–6Mg alloy specimens were modified using an ultrasonic impact treatment (UIT) process, which induces mechanical mixing of matrix and reinforces quasicrystalline (QC) Al63Cu25Fe12 particles to be introduced into a zone of severe plastic deformation. The wear and friction behaviours of the matrix alloy and QC reinforced layers were investigated in quasi-static and dynamic conditions with particular attention to the effects of QC particles size and test type on wear resistance and microhardness of sub-surface composite layers in Al–6Mg alloy. XRD and SEM analyses show that the layers of 40–50μm thickness are fabricated by the UIT process which contain homogeneously dispersed fine QCF (0.5–3μm) or coarse QCC (~15μm) particles, with volume fractions Vf of about 9% and 22%, respectively. In comparison to the annealed Al–6Mg alloy, noticeable increment in wear resistance was registered only for the composite layer reinforced with QCF particles. On the contrary, the QCC particles being fractured at the fabrication process and/or at the wear tests facilitate three-body abrasive wear conditions and deteriorate the wear resistance of the alloy. SEM and confocal laser microscopy show changes in wear mechanism from microcutting/ploughing in the QCF reinforced layer to microcracking/fracturing in the case of QCC reinforcement. Fine QCF particles are preferred for better wear resistance both at the quasi-static and dynamic conditions.