Elsevier

Scripta Materialia

Volume 43, Issue 11, 13 November 2000, Pages 1009-1013
Scripta Materialia

Effects of Sb addition on the microstructure and mechanical properties of az91 magnesium alloy

https://doi.org/10.1016/S1359-6462(00)00528-5Get rights and content

Introduction

The use of magnesium alloy casting in the automobile industry is projected to expand at an impressive rate in the next decade, which can cope with the energy and environment problems [1]. Alloy AZ91 (Mg-9Al-0.8Zn-0.2Mn) is the most favored magnesium alloy, being used in approximately 90% of all magnesium cast products [2]. It has excellent castability, sound room temperature (RT) mechanical properties and low cost. However, it suffers from low creep resistance at temperatures in excess of 120°C which makes it unsuitable for many of the components in automobile engines [3]. Although some magnesium alloys containing rare earth (RE) elements developed in the past few years [4] have good mechanical properties even at moderate temperatures, these alloys are more expensive than common Mg alloys such as AZ91. In addition to developing new alloy systems, optimization of existing alloys via trace element additions is a powerful route to the improvement of the performance of magnesium as a structural metal. Some surface active elements such as Ca, Sr and Bi can be used in the modification of β (Mg17Al12) phase, in changing the grain size, producing fine grain boundary precipitates for creep resistance and even increasing fluidity and castability of existing alloys [5]. The work reported here is a part of the program to develop cheap and creep resistant magnesium alloys based on AZ91. The aim of this paper focused on the influence of Sb addition on the microstructure and mechanical properties of AZ91 alloy at elevated temperatures up to 200°C.

Section snippets

Experimental

Four alloys of which the compositions are listed in Table 1 were prepared in a mild steel crucible under the protection of a mixed gas atmosphere of SF6 (1vol%) and CO2 (bal.) using commercial stock. The base composition of the alloys studied was Mg-9Al-0.8Zn-0.2Mn (alloy1) conformed to that of AZ91. Different amounts of antimony were added in the other alloys, so that the effects of antimony addition and variation of its concentrations on the microstructure and mechanical properties could be

Results

Table 1 lists the tensile data for all specimens tested. It can be seen that antimony addition to the AZ91 alloy resulted in significant influence on tensile properties. At both room temperature (RT) and elevated temperatures of 200°C, the yield strength significantly increased while the ductility decreased slightly with the increase of antimony addition. The maximums of yield strength were obtained from alloy3 containing 0.35% of Sb. Further increase of Sb addition resulted in a slight

Discussion

The results of the present work show that Sb addition to AZ91 alloy increases the yield strength at both ambient and elevated temperatures up to 200°C. The solubility of Sb in the AZ91 matrix is very low, hence the obvious mechanism by which Sb strengthens the AZ91-based alloy is precipitation hardening. The precipitates formed by Sb addition in AZ91 alloy have been found to be Mg3Sb2. These rod-shaped precipitates straddled the grain boundaries and some reached into both grains (see Fig. 3).

Conclusion

Small amount of antimony additions to the Mg-9Al-0.8Zn (AZ91) based alloys resulted in significant increases in yield strength and creep resistance at elevated temperatures up to 200°C, but slight decreases of ductility. Results of microanalysis indicate that the addition of Sb causes the formation of some rod-shaped precipitates Mg3Sb2 with hexagonal D52 structure which strengthens both matrix and grain boundaries effectively.

First page preview

First page preview
Click to open first page preview

References (7)

  • M Regev et al.

    Mater. Sci. Eng. A

    (1997)
  • P Humble

    Mater. Forum

    (1997)
  • A. Luo and M. Ö. Pekgüleryüz, J. Mater. Sci. 29, 5259...
There are more references available in the full text version of this article.

Cited by (139)

  • Enhancing mechanical properties of squeeze-cast AZ91 magnesium alloy by combined additions of Sb and SiC nanoparticles

    2021, Materials Science and Engineering: A
    Citation Excerpt :

    The incorporation of Sb into the AZ91 alloy up to 0.6 (wt. %) resulted in a substantial reduction of grain size and enhanced the mechanical properties including creep response of the AZ91 alloy owing to the Mg3Sb2 phase formation at the grain boundaries [7–11]. Nevertheless, these properties reduced drastically as the content of Sb increased beyond 0.6 (wt.

View all citing articles on Scopus
View full text