Effect of length scale of alumina particles of different sizes on the damping characteristics of an Al–Mg alloy

doi:10.1016/j.msea.2005.10.070

Materials Science and Engineering: A

Volume 423, Issues 1–2, 15 May 2006, Pages 189-191

https://doi.org/10.1016/j.msea.2005.10.070 Get rights and content

Abstract

Pure Al was reinforced with alumina particles with size ranging from micro to nano-size dimension. Magnesium was added to the Al matrix to enhance the wettability of alumina particles. Synthesis of materials was accomplished using the solidification route viz., disintegrated melt deposition technique. Energy dissipation in the form of damping capacity was determined using free–free type suspended beam arrangement coupled with circle-fit approach. Three samples with Al–4 wt.% Mg matrix were prepared that were reinforced by alumina particles whose size ranged from μm to nm length scale (viz., 10, 0.3 μm and 50 nm and with a volume percentage of 10.13, 1.47 and 0.94, respectively). Damping per unit volume percentage of alumina particles in the Al–Mg matrix increased by 58%, 30% and 3% for the alumina particles size of 50 nm, 0.3 and 10 μm, respectively, with respect to the monolithic Al–Mg specimen. Such increase in damping can be rationalized in terms of microstructural changes that arise due to the presence of the alumina particles in the composite samples compared to that of unreinforced sample.

Introduction

Stiffer and highly damping metals are actively sought for dynamic mechanical systems such as in spacecrafts, semiconductor equipments and robotics. Al exhibits such properties especially when it is unified with ceramic particles such as SiC [1]. Another widely used ceramic reinforcement is Al₂O₃ which is more inert than SiC in Al and is resistant towards oxidation. The results of the literature search, however, reveal that no attempt is made to investigate the effect of Al₂O₃ particle size on the damping behavior of aluminium–magnesium materials. In addition, the damping characterization using the methodology of impact-based measurement coupled with the unique circle-fit approach is also never attempted [2].

Research findings also reveal that when the microstuctural features such as reinforcement dimension approaches less than 100 nm, the material exhibits novel behavior which has grown into a special field of materials called nano-materials (NM) [3], [4]. In the present study, damping capacity which indirectly signifies internal friction of a material [5] is investigated for Al–Mg based formulations as a function of length scale of alumina reinforcement. In order to overcome the problem of poor wettability of Al₂O₃ by Al, either the matrix is alloyed or the reinforcement is surface coated. Study shows presence of MgO on the surfaces of Al₂O₃ improves wettability [6], hence Mg is added to the pure Al matrix in the present study.

Section snippets

Materials and processes

In the present study the disintegrated deposition method (DMD) [2] was adopted which involved heating the matrix (Al and Mg) to 750 °C under inert atmosphere and the alumina particles were added using a vibratory feeder which were additionally preheated for an hour at 500 °C before incorporation. To ensure uniform mixing the melt was continuously stirred at 450 rpm using a twin blade (pitch 45°) mild steel stirrer coated with Zirtex™ so as to avoid iron contamination. The total time for the

Results and discussion

The suspended beam experimental method was found to be highly repeatable and had many advantages for determining the damping factor of MMC samples. Previous studies on pure Al and Mg have clearly demonstrated the accuracy and repeatability of this testing method [1], [2].

Close inspection of the alumina particle at high magnification illustrated good particle-matrix interfacial bonding in all the three composites investigated in the present study. This can be partly attributed to the efficacy of

Conclusions

(i)
Presence of alumina particles in Al matrix enhances energy dissipation irrespective of their size due to the various intrinsic damping mechanisms acting parallel.
(ii)
The damping of Al increases with a decrease in alumina particle size for a fixed amount of alumina reinforcement. This can primarily be explained due to increase in dislocation density arising from an increase in surface area with a decrease in particle size.

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Effect of length scale of alumina particles of different sizes on the damping characteristics of an Al–Mg alloy

Abstract

Introduction

Section snippets

Materials and processes

Results and discussion

Conclusions

Mater. Res. Bull.

Acta Mater.

Mater. Sci. Eng.

Key Eng. Mater.

Int. Mater. Rev.

Anelastic Relaxation in Crystalline Solids