The introduction of modern technologies in materials science opens up new horizons for the creation of composite materials with improved properties. Aluminum matrix composites (AMCs) reinforced with particles or fibers have attracted considerable attention due to their high strength-to-weight ratio, good corrosion resistance, and processability. This paper investigates the effect of ultrasonic impact treatment (UST) on the structure, microhardness, and damping properties of AMCs reinforced with AlCuFe or titanium (Ti) intermetallic compounds.
The matrix was aluminum alloy of the 6061 series. The reinforcing particles were intermetallic AlCuFe of quasi-crystalline structure and titanium powder. Composites were obtained by powder metallurgy with subsequent extrusion. Samples were subjected to ultrasonic treatment with different parameters of action (frequency, amplitude, treatment time). Structural studies were carried out using optical and scanning electron microscopy (SEM). Microhardness was measured using the Vickers method. Damping characteristics were estimated by the logarithmic decrement of attenuation method.
The surface layers of aluminum and the damping characteristics were studied, and a highly oriented fine-grained structure with grain sizes from 0.1 to 0.53 μm was observed. It is important to note that the structure of dislocation cells is formed only after ultrasonic impact vibration treatment (UIV). The results show the formation of composite layers with a relatively uniform distribution of reinforcing particles, the volume fraction of which is about 0.17.
In the UIV process, finely dispersed powders are used to modify the near-surface layers of aluminum. The effect of icosahedral quasicrystal (QC) AlCuFe and hexagonal Ti added to the strengthening zone is investigated. It is found that the quasicrystal reinforcement is characterized by a semi-coherent interface between the particles and the matrix, while Ti particles exhibit strong adhesion to the aluminum matrix due to the formation of Ti.
The AlCuFe-reinforced composite layer exhibits micro-dimensionality, while the Ti-reinforced layer has an average grain size of 0.5–2 μm. These microstructural features result in a significant improvement in the microhardness and damping properties of the treated aluminum samples. Much higher values of microhardness (about 1.3 GPa) and logarithmic decrement (about 12 × 10−4) were recorded for the aluminum samples with the QC composite layer, compared to the samples containing the Ti layer (about 1 GPa and 3.6 × 10−4) and quenched aluminum (0.58 GPa and 1.4 × 10−4). This is explained by (i) the smallest grain size, (ii) the semi-coherent interaction of the particles with the matrix and (iii) the high hardness and specific rigidity of the AlCuFe QC phase. Even after heating to 623 K, the aluminum samples coated with composite layers with QC and Ti retain a relatively high level of microhardness (about 1.1 GPa and 0.8 GPa) and logarithmic decrement (about 5 × 10−4 and 2 × 10−4).
USUO leads to a significant refinement of the aluminum matrix grain and a more uniform distribution of reinforcing particles. Near the surface of the samples, the formation of a nanocrystalline structure is observed. The microhardness of composites subjected to USUO increases significantly compared to untreated samples. Damping characteristics also improve after USUO, which is associated with an increase in the number of grain boundaries and dislocations that facilitate the dissipation of vibration energy.
Ultrasonic impact treatment is an effective method to improve the structure, microhardness and damping characteristics of AlCuFe or Ti-reinforced AMCs. The results obtained can be used to develop new AMCs with improved performance characteristics for applications in aviation, automotive and other industries.
Author: BN Mordyuk, MO Iefimov, GI Prokopenko, TV Golub, MI Danylenko
Institute: G. V. Kurdyumov Institute of Metal Physics, Academician Vernadsky Boulevard, 36, UA-03680, Kyiv, Ukraine, Fraunhofer Institute for Materials Science, Krzyzhanovsky St., 3, UA-03142, Kyiv, Ukraine