THE INFLUENCE OF Zn AND Ca ON TENSILE PROPERTIES AND CREEP RESISTANCE OF MgSn6 ALLOY

In the paper the role of Zn and Ca in enhancement of creep resistance of MgSn6 alloy has been investigated. The influence of zinc on thermal stability of Mg₂Sn phase has been evaluated as well. Three alloys in as-cast and heat-treated condition have been chosen as a research material – MgSn6, MgSn6Zn1,5 and MgSn6Zn1,5Ca1. The microstructure of investigated alloys has been analysed using the scanning electron microscope, coupled with EDS spectrometer to enable the analysis of chemical composition of individual microstructural constituents. Creep tests have been performed. It has been revealed, that the microstructure of MgSn6 alloy consists of α-Mg matrix and α-Mg+Mg₂Sn eutectic compound. The addition of Zn caused changes in the morphology of α-Mg+Mg₂Sn eutectic compound and formation of Zn-rich phase. Two forms (coarse rod-like primary and lamellar secondary) of CaMgSn phase have been observed in the alloy, containing Ca. It has been found that Zn does not influence the morphology and crystallisation process of Mg₂Sn phase, which is less thermally stable than CaMgSn phase. Hence, the CaMgSn phase might have a negative influence on creep resistance of MgSn6 alloy. The best creep properties have been exhibited by MgSn6Zn1,5 alloy after age-hardening treatment.