Dependence of internal friction of fibre-reinforced and unreinforced AZ91 on heat treatment

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2002-02, Vol.324 (1), p.127-133
• Main Authors: Göken, J, Riehemann, W
• Format: Article
• Language: English
• Subjects: Applied sciences; AZ91; Crack; Dislocation damping; Exact sciences and technology; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Other mechanical properties; Precipitation; Reinforcement; Saffil
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(01)01294-1

Damping measurements have been carried out on the widely used commercial magnesium alloy AZ91 both unreinforced and reinforced with δ-alumina short fibres by the melt infiltration technique. The damping was determined after isochronal heat treatments by the measurement of the logarithmic decrement of free bending beam vibrations at frequencies ranging from 65 to 85 Hz. The thermoelastic and external apparatus damping were subtracted to obtain the damping, which can be mostly attributed to the dislocation movement. A maximum hardness and internal friction as a function of the annealing temperature at about 260°C both for unreinforced and reinforced AZ91 was found. This could be correlated with the precipitation of Mg 17Al 12 (β-phase). In comparison with the unreinforced AZ91 for the composite a general increase in damping was observed. All measurements of the logarithmic decrement up to an annealing temperature of about 413°C were explained by a model of Granato and Lücke. For higher temperatures a strong increase in damping could be observed and was correlated with the formation of cracks.