An analysis of microstructure and impression creep response of squeeze-cast AZ91–xBi–ySr alloys

ABSTRACT

The present investigation deals with the microstructural modification following the Bi + Sr additions to the squeeze-cast AZ91 alloy and its effect on impression creep response. The Bi + Sr additions form the Al₄Sr and Sr₂Bi phases besides the α-Mg and β-Mg₁₇Al₁₂ phases, and improves creep resistance of the AZ91 alloy. The AZ91 + 1.0Bi + 0.5Sr alloy reveals the best creep resistance among the alloys. The stress exponent and the activation energy values of all the alloys are in the range of 4–7 and 100.2–112.7 kJ mol⁻¹, respectively, depicting the pipe diffusion-controlled dislocation creep is the governing creep mechanism. The post-creep microstructural study confirms several dislocations pile-ups around the Al₄Sr and Sr₂Bi phases resulting in improved creep resistance of the modified AZ91 alloys.

KEYWORDS:

• AZ91 magnesium alloy
• squeeze-casting
• microstructure
• intermetallic phase
• impression creep
• dislocation creep
• dislocation pile-up
• diffusion coefficient

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was financially supported by the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), New Delhi, India through DST No: SB/FTP/ETA-0270/2012/1, dated: 20-05-2013. The authors would also like to thank the Council of Scientific and Industrial Research (CSIR), New Delhi, India for sanctioning the impression creep testing set up employed in the present investigation through Scheme No.: 22(626)/13-EMR-II, dated: 26-02-2013.