Ludmila Parashkevova

Modelling of Light Mg and Al Based Alloys as “in situ” Composites

The present paper is aimed to further elucidate the microstructure properties relationship of light alloys containing additional hard particles. The materials studded are magnesium alloys from the system AZ (Mg–Al–Mn–Zn) and mechanically alloyed aluminum reinforced with carbide and oxide particles. Strengthening and hardening phenomena in Metal Matrix Multiphase heterogeneous Materials (MMMM) are considered in this study from the view point of mechanics of nano- and micro-composites. A semi-analytical approach is adopted taking into account the manufacturing processing and microstructure features. Multilevel homogenization procedure is performed, accounting for size effects. In the model applied the metal matrix is considered as an elastic–plastic micropolar media and the hard phases (precipitations Mg17Al12, TiC, Al4C3, Al2O3) are treated as conventional elastic Cauchy materials. Experimentally observed dependence of the characteristic matrix length on the volume fraction of the hardening phases is modeled and numerically simulated in the case of ball-milled Al alloyed with Al4C3 and Al2O3. For AZ alloys the impact of intermetallic phase Mg17Al12 is discussed in the frame of presented composite model and the strengthening effect of the addition of small amount of TiC is estimated.

Investigation of As-cast Light Alloys by Selected Homogenization Techniques with Microstructure Effects

In the present contribution, upgrading the findings of previous works, [1, 2], new models are proposed for evaluation of effective mechanical properties of light alloys regarded as multiphase composites. These models are aimed to improve the mechanical properties predictions of two groups light alloys: die cast Mg alloys AZ and metal foams with closed cells. The presented models are variants of Mean Field Homogenization (MFH) approach and Differential Homogenization Method, (DHM), both accounting for microstructure size effects. They are appropriate for composite structures where the content of non- matrix phases is predominant. The microstructure - properties relationships for AZ Mg alloy with Continuous (C) and Discontinuous (D) intermetallic phase precipitations are investigated applying MFH and DHM approaches. The basic distinction between cases (C) and (D) consists of different arrangement and volume fraction of harder intermetallic phase Mg17Al12. The type of the microstructure observed depends mainly on the applied cooling regime and chemical composition of the alloy. The elastic-plastic properties predictions for both types of microstructure topology are compared and discussed. The elastic behavior of foams with closed pores is simulated applying DHM, where the size sensitive variant of Mori-Tanaka scheme is used as a basic ‘dilute case’ procedure. The method is developed to closed form solutions of corresponding system of differential equations. The results obtained by means of the size-sensitive DHM are compared with experimental data for aluminium and glass foams taken from the literature.

ELASTIC PLASTIC PROPERTIES OF MULTIPHASE COMPOSITE BASED ON NON HOMOGENEOUS METAL MATRIX – MODELLING AND SIMULATION

Abstract A new approach for estimating the mechanical properties of multiphase composite is proposed. The Representative Volume Element (RVE) of the material consists of two different metal matrices and arbitrary number of elastic hardening phases. Multistep homogenization procedures are applied, accounting for influence of the constituent properties, sizes, volume fractions and microstructural distributions. Modified Mori-Tanaka homogenization technique for micropolar media and Budiansky self-consistent method are used for estimation the overall properties of the composite. The theoretical model is applied to description of the properties of precipitation hardening rapidly solidified alloy of the system AlFeVSi with high content of Fe and Si.

Multiscale modeling of multiphase "in situ" composite

The elastic-plastic behaviour of rapidly solidified Al based (FeSi)-enriched alloys containing intermetallic compounds is considered. A new multilevel mechanical model for the “in situ” composite is proposed considering the aluminium matrix as a micropolar elastic plastic Cosserat material and the hardening phases as pure elastic ones. A two steps homogenization procedure is applied to obtain the overall properties of the multiphase “in situ“ composite, taking into account the existence of different sizes of intermetallic inclusions. A variational approach is applied to evaluate the equivalent stress on macro level at the transition from micro to macro scale. The model is developed using information provided by microstructural investigations and EDX analysis. The multistage bulk material manufacturing process from rapid solidified powders or ribbons is simulated using the Finite Element Method. The model is implemented as user subroutines into the FE code MARC. Numerical simulations are provided, corresponding to different values of metal forming parameters. The influence of the different inclusions sizes on the hardening behavior is discussed. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)