טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentCohen Shalom
SubjectPhase Formation, Precipitation and Strengthening Mechanisms
in Mg-Zn-Sn, Mg-Zn-Sn-Ca and Mg-Zn-Sn-Si Alloys
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Emeritus Menachem Bamberger


Abstract

A new type of magnesium alloy based on Mg-Zn-Sn system has been developed for possible use for high temperature applications. The widely used magnesium alloy belong to Mg-Zn-Al (AZ) series, such as AZ91 (Mg-9Al-1Zn) and AZ61 (Mg-6Al-1Zn), which have excellent castability, good room temperature mechanical properties and low cost. However, the AZ series posse's poor creep resistance at elevated temperature. The main reason for the poor creep resistance is the γ-Mg17Al11 phase, which precipitates at elevated temperatures and reduces the structural stability. This research Eliminated the γ-Mg17Al11 phase by replacing the Al by Zn and Sn. In addition 2 minor alloying elements Ca or Si were added to the Mg-Zn-Sn basic alloy. The research studies the microstructure and mechanical properties in the as cast condition, after solution treatments, exposures to elevated temperatures and precipitation hardening. Results show that the Mg-5%wtZn-5%wtSn alloy has good stability under high temperature of 200oC for 32 days. The response of this alloy to precipitation hardening is good with two maxima of hardness during the aging were found to be connected with the formation and coarsening of two types of precipitates MgZn and Mg2Sn. additions of Ca (1%wtCa) were found to be efficient in refining the microstructure and receiving very good casting appearance with a smooth, metallic bright surface. Additions of Si (1.5%wtSi) were results in better stability in high temperatures.