Dalibor Blažek

Internal Friction in Extruded Aluminium Alloy

Aluminium alloys have very useful properties. Because they are light, easily formed, machined and cast, they are widely used in aircraft industry and automotive industry. Their mechanical properties are mostly influenced by former mechanical and thermal treatment. An extruded aluminium alloy EN AW – 2007 was used in the as-received state and the specimens were thermally cycled with increasing the upper temperature step-by-step. After each thermal cycle the stress-amplitude dependence of internal friction was measured at room temperature. The quality factor Q-1 was measured by a resonant method at a frequency of 20 kHz. Thermal and mechanical treatments influenced the anelastic properties of the material. The thermal treatment affects the internal friction in a positive way, while the mechanical treatment decreases Q-1. The microstructural changes were observed by optical microscopy.

Amplitude Dependent Internal Friction of Magnesium Alloy AZ31 at Room Temperature

The aim of this work is to study the Amplitude Dependent Internal Friction (ADIF) of magnesium alloy AZ31 at room temperature at the frequency 20kHz. The internal friction of AZ31 at room temperature is mostly influenced by mechanical cycling at strain amplitudes in the microplastic deformation region. An excited state of the AZ31 alloy, which can be associated with a higher internal friction and lower dynamic modulus than usual state, was found immediately after mechanical cycling. When the strain amplitude drops, the diffusion of solute atoms restores the Zener atmosphere and the internal friction relaxes exponentially with the second root of time. The measurement methodology and obtained results are presented.