Abstract
Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. Overheating, hexachloroethane and wax-CaF2-carbon powder were applied. The research procedure comprised microstructure analysis by means of light microscopy, scanning electron microscopy and quantitative analysis with AnalySIS Pro® software and mechanical properties’ investigation. The microstructure of AZ91 alloy in the as-cast condition consists of α-Mg solid solution with precipitates of Mg17Al12, Mg2Si and Al8Mn5 phases. It was reported that all applied modifiers cause refinement of α-Mg solid solution grains and a decrease of the volume fraction of α-Mg+Mg17Al12 compound discontinuous precipitates. The best results were obtained in the case of wax-CaF2-carbon powder.
Highlights
Primary grain size is one of the elementary structural criteria in evaluation of the quality of cast magnesium alloys
Condition of AZ91 alloy in as-cast condition is composed of α-Mg solid solution with precipitates of Mg17 Al12 phase (Figure 2a)
The microstructure of AZ91 alloy in as-cast condition is composed of α-Mg solid solution with morphology were observed: precipitates of Mg17Al12 phase (Figure 2a)
Summary
Primary grain size is one of the elementary structural criteria in evaluation of the quality of cast magnesium alloys. The temperature applied during Elfinal process, which is lower than in case of overheating, makes this process more cost effective It enables holding the molten alloy at pouring temperature for at least one hour with no penalty to the efficiency of the grain refinement process [10]. Despite of the effectiveness of overheating and Elfinal processes in grain refinement, the problems connected with them caused the development of methods which apply the addition of carbon. These methods involve the introduction of carbon to molten magnesium alloy in the form of carbon gases (e.g., CO, CO2 , CH4 ), solid carbon One of them is wax-CaF2 -carbon powder, which is more eco-friendly and at the same time more effective in grain refinement [14]
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