DRUŠTVO LIVARJEV SLOVENIJESLOVENIAN FOUNDRYMEN SOCIETY
Član The World Foundry OrganizationMember of World Foundry Organization

INFLUENCE OF MG, CU AND FE ADDITION ON THE PROPERTIES OF HYPEREUTECTIC AL-SI ALLOYS

The AlSi9Cu3 alloy is one of the most widely used aluminium cast alloys, because of its good mechanical properties that are preserved even at elevated temperatures. The goal of this work was to analyze the process and the mechanisms that influence corrosion of the AlSi9Cu3 alloy. Several methods were used for characterization: chemical analysis, thermodynamic simulation of equilibrium phases, and metallographic analysis. Surface of corroded and not corroded sections of ingots of the AlSi9Cu3 alloy were analyzed. A reactor was designed to determine mechanisms that influenced corrosion of the AlSi9Cu3 alloy. Samples of the AlSi9Cu3 alloy and of electrolytic aluminium were inserted into the reactor. They were exposed to three different atmospheres: dry atmosphere, atmosphere humidified with distilled water, and atmosphere humidified with water from a foundry cooling system. Macroscopic and microscopic analyses showed that samples of the AlSi9Cu3 alloy corroded at fastest in the atmosphere humidified with water from foundry cooling system. Microscopic analyses and reference data gave evidence that pitting corrosion and intergranular corrosion took place on the ingot surface of the AlSi9Cu3 alloy.
Key words: corrosion, atmospheres, AlSi9Cu3 alloy.

INFLUENCE OF COOLING RATE ON THE MICROSTRUCTURE DEVELOPMENT IN THE ALMG9 ALLOY

Foundry Al-Mg alloys assigned to high pressure die casting have imposed themselves in recent times due to their high strength and ability of precipitation hardening for compositions above 7 wt. % Mg. The influence of the cooling rate on the significant temperatures of phase changes during solidification and the grain size of AlMg9 alloy were investigated in this paper. Cooling was performed by the established rates of 5, 15, 30 and 100 [K/s]. Phase changes were accompanied and identified through simultaneous and simple thermal analysis. Physical models of the significant temperature and cooling rate dependence were set up. Solidification simulation was performed through the finite elements method by the ProCast program, which was compared with the real cooling curves. Beside this, the grain size (G) and the number of grains per surface area (NA) for each cooling rate were determined as well as their correlation. Microstructure analysis was performed on the optical, as well as on the scanning electron microscope (SEM) which results in visual recognition of individual phases on their morphology basis. Chemical composition determination of each phase was carried out by the energy dispersive specter (EDS). Phases Alx(MnFe)ySiz, Mg2Si and Al2Mg were determined in the microstructure.
Key words: Al-Mg alloy, cooling rate, microstructure, grain size.