Microstructure and Impression Creep Behaviour of AZ91 Alloy with Trace Additions of Sb and Sr

Abstract

In this current research,the microstructure and impression creep behaviour of AZ91 alloy with trace additions of Sb and Sr have been investigated. The fabricated alloys using squeeze casting technique are AZ91, AZJ910 (AZ91-0.3Sr), AZY910 (AZ91-0.5Sb) and AZJY9100 (AZ91-0.5Sb-0.3Sr). A thorough icrostructural examination has been done on all the fabricated alloys. The impression creep test was conducted on all the alloys in the stress range of 300-480 MPa and in the temperature range 423 -523 K under the dwell time 7200 sec. The results reveal that addition of alloying elements refines the grain size and β-Mg 17
Al 12phase in the alloy, which is more effective with the combined addition. Apart from α-Mg and β-Mg17 Al12 phases, an irregular shaped Al4 Sr phases new and rod-shaped Mg3 Sb2 phases have formed following the addition of Sr and Sb in the AZ91 alloy, respectively. In case of combined additions, both Al4 Sr and Mg3 Sb 2 phases have formed. Among the alloys, the modified alloys show better creep behaviour than the AZ91 base alloy. The combined additions of Sb and Sr are more efficient in increasing creep resistance than the single additions due to the reduced amount of β-Mg 17Al 12 phase and presence of thermally stable Mg3 Sb2 and Al4 Sr phases at grain boundaries. Post creep microstructural examination reveals that the intermetallic phases have an ability to act as a barrier for dislocation movement during creep test. The stress exponent values(n) and activation energy (Q) values are in the range of 4.6–6.3 and 104.1 ± 2.4 to 114.9 ± 1.6 kJ/mol, which suggested that the governing creep mechanism was dislocation climb aided by pipe diffusion for all the temperatu res and stress range employed.