טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAlexey Zilberov
SubjectDevelopment of Creep Resistant Mg-Ca-Zn and Mg-Ca-Zn-Si
Casting Alloys
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Emeritus Bamberger Menachem


Abstract

In this research, the precipitation process at Mg-Zn-Ca and Mg-Ca-Zn-Si alloy was studied at the as-cast condition in order to investigate the behavior of this alloy at elevated temperatures. In addition, the alloy was solution treated in order to allow better understanding of the precipitation mechanisms and test the alloy’s response to precipitation hardening

Based on thermodynamic precipitation hardening calculations, an alloy containing Mg-3.2wt%Zn-1.5 wt%Ca was chosen as the master alloy.  Zn dissolves well in Mg and can participate in solution hardening, while Ca improves the corrosion resistance, and together with Zn can create the stable intermetallic Mg6Zn3Ca2.

The alloy was examined in the as-cast condition, after solution treatment (held at 300ºC for 48h, then heated to 465ºC for another 96hr.), and after several aging periods and temperatures (175ºC-250ºC for 1-96hr.), SEM and XRD examination of the as-cast alloy reveals the coexistence of 3 phases, an Mg matrix, the ternary Mg6Zn3Ca2 intermetallic on the grain boundaries and large precipitates of Mg2Ca intermetallic in the Mg matrix

The effect of adding small amounts of Si 0.1 wt %( low Si) and 0.4%wt (high Si) on the hardening was investigated. The alloys ware examined in the as-cast condition, after solution treatment (held at 300ºC for 48h, then heated to 455ºC for another 96hr.), and after several aging periods and temperatures (175ºC-250ºC for 1-96hr.).

SEM and XRD examination of the as-cast alloys has shown the following phases; Mg matrix, and the ternary Mg6Zn3Ca2 intermetallic on the grain boundaries in both alloys.