Effect of Ultrasonic Treatment in the Static and Dynamic Mechanical Behavior of AZ91D Mg Alloy

Helder Puga,Vanessa Vieira,Joaquim Barbosa,Vitor Carneiro

doi:10.3390/met5042210

Abstract

The present study evaluates the effect of high-intensity ultrasound (US) in the static and dynamic mechanical behavior of AZ91D by microstructural modification. The characterization of samples revealed that US treatment promoted the refinement of dendrite cell size, reduced the thickness, and changed the β-Mg17Al12 intermetallic phase to a globular shape, promoted its uniform distribution along the grain boundaries and reduced the level of porosity. In addition to microstructure refinement, US treatment improved the alloy mechanical properties, namely the ultimate tensile strength (40.7%) and extension (150%) by comparison with values obtained for castings produced without US vibration. Moreover, it is suggested that the internal friction, enhanced by the reduction of grain size, is compensated by the homogenization of the secondary phase and reduction of porosity. It seems that by the use of US treatment, it is possible to enhance static mechanical properties without compromising the damping properties in AZ91D alloys.

Highlights

Mg alloys are a promising candidate for applications involving low-weight and high-damping characteristics
Metallic materials have relatively low damping, Mg alloys, in addition to their very low density, possess the highest damping capacity among metals [1]. They are characterized by a relatively low elastic modulus and mechanical strength. This dependence between static and dynamic mechanical properties is a common feature of metals, given that high-damping materials are generally unsuitable in many structural applications [2]
This paper presents and discusses the effect of ultrasonic treatment in the microstructure and the static/dynamic mechanical behavior of AZ91D alloy cast in a permanent mold by applying ultrasound indirectly to the melt during the first stages of solidification

Summary

Introduction

Mg alloys are a promising candidate for applications involving low-weight and high-damping characteristics. As for the dynamic mechanical properties, it is desirable to obtain materials with high damping properties, i.e., a high ability to dissipate elastic strain energy during mechanical vibration or wave propagation [2] This energy dissipation is promoted by the internal friction generated through inelastic relaxation and/or thermal activation. The presence of point defect relaxation, dislocation mechanisms, interfaces, and their combination with thermal activation processes are the main cause of internal friction They are associated with the morphology of the microstructure, namely by the secondary phases, impurity atoms [5], porosity, grain size, and boundaries [5,6]. Thermal currents and the stress generated by inhomogenities and individual anisotropic elastic crystals enhance damping in macroscopic polycrystalline metals [16] This activation, promoted by external thermal energy, is dependent to the temperature, frequency, impurities, and microstructural morphology [17]. This paper presents and discusses the effect of ultrasonic treatment in the microstructure and the static/dynamic mechanical behavior of AZ91D alloy cast in a permanent mold by applying ultrasound indirectly to the melt during the first stages of solidification

Experimental Section

Results and Discussion

Conclusions