KOMPOZYTY (COMPOSITES) 4(2004)10 Pavel Lukáč 1 , Zuzanka Trojanová 2 , Alexandra Rudajevová 3 Charles University, Ke Karlovu 5, 12116 Praha 2, Czech Republic PROPERTIES OF MAGNESIUM BASED COMPOSITES Mg-based composites were manufactured by various processing techniques. The reinforcement was in the form of short fi- bres or particles. The microstructure developed influences properties of composites. Physical and mechanical properties of Mg based composites were investigated in the temperature range from 293 to 673 K. The thermal expansions and thermal conductivity were measured. Strength and deformation behaviour were studied. The volume fraction, shape and composition of the reinforcement significantly influence the properties of a composite. The interface between the matrix and the reinforcement has a great deal of importance in determining the properties of the composite. Key words: Mg composite, thermal and mechanical properties WŁAŚCIWOŚCI KOMPOZYTÓW NA OSNOWIE MAGNEZU Przedstawiono wyniki badań właściwości fizycznych i mechanicznych kompozytów magnezowych. Materiały na osnowie ma- gnezu i jego stopów AZ91 oraz QE22 wytworzono różnymi metodami. Fazę umacniającą stanowiły krótkie włókna δ-Al2O3 oraz cząstki ceramiczne SiC. Badania rozszerzalności cieplnej, przewodności cieplnej oraz właściwości wytrzyma- łościowe kompozytów, jak i stopów osnowy przeprowadzono w zakresie temperatur od 293 do 673 K. Określono jednoznaczny wpływ udziału objętościowego, kształtu oraz składu chemicznego fazy umacniającej na właściwości kompozytów. Uwzględniono również znaczący wpływ granic rozdziału pomiędzy osnową i fazą umacniającą w kształtowaniu właściwości materiałów kompo- zytowych. Słowa kluczowe: kompozyty magnezowe, właściwości cieplne i mechaniczne 1, 2 Prof. RNDr., Dr Sc, 3 RNDr., CSc INTRODUCTION There is an increasing interest in the automobile industry for light metal matrix composites (MMC). Ma- gnesium alloys as the lightest alloys may be used as a structural metal because they have high specific strength and specific elastic modulus. On the other hand, Mg alloys exhibit poor plastic formability due to their hexa- gonal close packed structure. Reinforcement of an alloy leads to an increase in strength. Grain refinement leads also to a higher strength and higher ductility of the al- loys. Thermal residual stresses are formed in MMCs due to differences in the coefficients of thermal expansion between the matrix and the reinforcement. The ma- trix/reinforcement interface is significant in determining mechanical properties. In general, composite properties strongly depend on the properties of the composite com- ponents. The aim of this paper is to show the influence of tem- perature on the strength and thermal properties of some Mg based composites. EXPERIMENTAL PROCEDURE The investigated materials were Mg and its alloys reinforced with δ-Al 2 O 3 short fibres (Saffil ® with a mean diameter of 3 μm and a mean length about 87 μm) pre- pared by squeeze casting technology. The preforms con- sisting of Al 2 O 3 short fibres showing a planar isotropic distribution and a binder system (containing Al 2 O 3 and starch) were preheated to a temperature higher than the melt temperature of magnesium (to about 1000°C) and then inserted into preheated die (290 to 360°C). The pressure for forcing the melt into the die with the preform was applied in two steps (50 MPa for 10 s and 130 MPa for 60 s). The second step closes pores and shrinkage cavities. During this short time of contact between the liquid metal and the fibres, only a slight reaction between the fibres and the matrix can occur. QE22 (Mg-2% Ag-2% rare earths) alloys reinforced with SiC particles were fabricated by mixing and milling of matrix powder and particles with subsequent hot extrusion of the milled products. The Mg 2 Si products were formed around the SiC particles in the SiCp/QE22 composites.