ARCHIVES of FOUNDRY ENGINEERING Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences ISSN (1897-3310) Volume 7 Issue 1/2007 179 – 182 39/1 Microstructure of MCMgAl12Zn1 magnesium alloy L.A. Dobrzański a, *, T. Tański a , L. Čížek b a Division of Materials Processing Technology and Computer Techniques in Materials Science, Institute of Engineering Materials and Biomaterials, Silesian University of Technology, Konarskiego St. 18a, 44-100 Gliwice, Poland b Faculty of Metallurgy and Materials Engineering, Technical University of Ostrava, Tř.17 Listopadu 15, 708 33 Ostrava, Czech Republic *Corresponding author. E-mail address: leszek.dobrzanski@polsl.pl Received 08.02.2007; Approved for print on: 12.03.2007 Abstract In this paper is presented the structure of the cast magnesium alloys as cast state and after heat treatment cooled with different cooling rate, depending on the cooling medium (furnace, water, air). For investigations samples in shape of 250x150x25 mm plates were used. The structure have been study in the light microscope, scanning electron microscope equipped with an electron back scattering facility. The effects of the addition of Al on the microstructure were also studied. In the analysed alloys a structure of α solid solution and fragile phase β (Mg 17 Al 12 ) occurred mainly on grain borders as well as eutectic and phase with Mn, Fe and Si. Investigation are carried out for the reason of chemical composition influence and precipitation processes influence to the structure and mechanical properties of the magnesium cast alloys with different chemical composition in as cast alloys and after heat treatment. Keywords: Heat Treatment; Manufacturing and processing; Mechanical Properties; Fracture Mechanics; Magnesium alloys 1. Introduction At the contemporary stage of the development of the engineering thought, and the product technology itself, material engineering has entered the period of new possibilities of designing and manufacturing of elements, introducing new methods of melting, casting, forming, and heat treatment of the casting materials, finding wider and wider applications in many industry branches. Engineers whose employment calls for significant expenditure of labour and costs strive to reduce material consumption. Therefore the development of engineering aims at designs optimizing, reducing dimensions, weight, and extending the life of devices as well as improving their reliability [1, 2, 4]. The material selection is preceded by the analysis of many factors like: mechanical, design, environmental, urbanization, recycling, cost, availability, and weight related issues, which may change the existing conditions and emerge the needs resulting from the supplier-customer relation [5, 9, 10]. The strive to decrease the weight of products becomes an important challenge for designers and process engineers. The excessive weight verifies a significant extent the possibilities of employing particular material groups. Contemporary materials should possess high mechanical properties, physical and chemical, as well as technological ones, to ensure long and reliable use. The above requirements and expectations regarding the contemporary materials are met by the non-ferrous metals alloys used nowadays, including the magnesium alloys. Magnesium alloys and their derivatives, alike materials from the lightweight and ultra-lightweight family, characterize of low density (1.3-1.8 g/cm 3 ) and high strength in relation to their weight [1-4, 6-8]. Moreover, the magnesium alloys demonstrate good corrosion resistance, no aggressiveness towards the mould material and low heat of fusion, which make it possible to use pressure die casting that ensures good shape reproducibility. The magnesium alloys are widely used in the automotive industry. The concrete examples of the employment of castings ARCHIVES of FOUNDRY ENGINEERING Volume 7, Issue 1/2007, 179-182 179