HIGH STRAIN RATE BEHAVIOUR OF AN AZ31 + 0.5 Ca MAGNESIUM ALLOY

<em>The paper reports behaviour of magnesium alloy AZ31 (nominal composition 3 % Al - 1 % Zn – balance Mg) with an addition of 0.5 wt. % Ca at high strain rates. Samples were prepared by the squeeze cast technology. Dynamic compression Hopkinson tests were performed at room temperature with impact velocities ranging from 11.2 to 21.9 m.s^-1. A rapid increase of the flow stress and the strain rate sensitivity was observed at high strain rates. Transmission electron microscopy showed extremely high dislocation density and mechanical twins of two types. Adiabatic shear banding is discussed as the reason for the observed behaviour at high strain rates.</em><span> </span

Superplastic Behaviour of an Mg-Ag-RE Magnesium Alloy

Fine-grained magnesium alloy QE22 (Mg-2.5wt.%Ag-2.5wt.%RE-0.6wt.%Zr) was prepared from cast ingot which was submitted to a two stages heat treatment. Subsequently the billet was overaged and extruded at high temperature. Samples were deformed at elevated temperatures from 380 °C up to 480 °C at various strain rates. Microstructure of deformed samples was studied using light and electron microscopy. Conditions for superplasticity of the investigated alloys have been estimated. Possible deformation mechanisms are discussed.JRC.F.4-Innovative Technologies for Nuclear Reactor Safet

Influence of processing techniques on microstructure and mechanical properties of a biodegradable Mg-3Zn-2Ca alloy

New Mg-3Zn-2Ca magnesium alloy was prepared using different processing techniques: gravity casting as well as squeeze casting in liquid and semisolid states. Materials were further thermally treated; thermal treatment of the gravity cast alloy was additionally combined with the equal channel angular pressing (ECAP). Alloy processed by the squeeze casting in liquid as well as in semisolid state exhibit improved plasticity; the ECAP processing positively influenced both the tensile and compressive characteristics of the alloy. Applied heat treatment influenced the distribution and chemical composition of present intermetallic phases. Influence of particular processing techniques, heat treatment, and intermetallic phase distribution is thoroughly discussed in relation to mechanical behavior of presented alloys.Web of Science911art. no. 88

Superplastic Behaviour of Selected Magnesium Alloys

Superplastic materials exhibit anomalous plasticity, achieving strain until several thousand per cent. The phenomenon of plasticity is limited on special microstructure, temperatures and strain rates. Magnesium and magnesium alloys are known as materials with limited plasticity. This is due to their hexagonal structure of these materials. Finding the superplasticity conditions has a crucial importance for applications of magnesium alloys. In this chapter, we will deal with the superplastic behaviour of AZ91, QE22, AE42 and EZ33 magnesium alloys. Materials were prepared by various techniques: thermomechanical treatments, equal channel angular pressing, hot extrusion, rolling, friction stirring and high-pressure torsion. Strain rate sensitivity and elongation to fracture were estimated at various temperatures. Mechanisms of superplastic flow are discussed. Grain boundary sliding and diffusional processes were depicted as the main mechanisms responsible for high plasticity of these alloys. On the other hand, cavitation at elevated temperatures deteriorates the superplastic properties

Internal Friction in Magnesium Alloys and Magnesium Alloys- Based Composites

In practice, some problems connected with undesirable mechanical vibrations or interruption of acoustic bridges may be solved using high damping materials. Especially, transport industry needs high damping light materials with proper mechanical properties. Magnesium alloys and magnesium alloys‐based metal matrix composites may be considered as materials exhibiting such behaviour. Damping of mechanical vibrations and their conversion to the heat (internal friction) is conditioned by the movement and redistribution of various defects in the crystal lattice. Generally, internal friction depends on the material microstructure and conversely changes in the material microstructure may be studied using the internal friction measurements. The strain amplitude‐dependent internal friction was investigated at room temperature in commercially available Mg alloys and Mg alloys‐based composites with the aim to identify changes in the microstructure invoked by thermal and mechanical loading. The temperature‐dependent internal friction indicated the following effects: (a) mechanisms connected with dislocations and grain boundaries in the microcrystalline pure Mg, (b) precipitation and phase transformations in alloys and (c) generation as well as relaxations of thermal stresses in composites. The internal friction was measured in the bending mode in two frequency regions: I.: units and tens of Hz and II.: units of kHz

Magnesium Alloys Based Composites

Metal matrix composites (MMCs) based on magnesium alloys are excellent candidates for engineering light structure materials, and have great potential in automotive, high performance defence and aerospace applications. In spite of relatively high number of papers dealing with microstructure and mechanical properties of MMCs based on Mg alloys, the deformation mechanisms and other physical properties of these materials are not known enough.The objective of this chapter is to reveal influence of various reinforcement types on the mechanical and physical behaviour of composites in which various magnesium alloys were reinforced with short alumina (Saffil®) fibres and/or SiC and Si particles.JRC.F.4-Safety of future nuclear reactor