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Microstructure Evolution and Mechanical Properties of the AZ91 Magnesium Alloy with Sr and Ti Additions in the As-Cast and As-Aged Conditions

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Abstract

Effect of different amounts of Sr and Ti additions with T6 heat treatment on microstructure and mechanical properties of the AZ91 alloy was investigated. The microstructure of the AZ91 alloy is consisted of the α-Mg phase surrounded by the semicontinuous network of β-Mg17Al12 intermetallics. The average grain size and volume fraction of β phase decreased up to 1 wt.% Sr and 0.1 wt.% Ti additions. Exceeding Ti additions led to increase in both grain size and volume fraction. It was found that the grain refinement mechanism of AZ91 alloys with Sr additions was grain restriction factor. Also, 0.1 wt.% Ti addition could refine the grain structure of the AZ91 alloy by the formation of Al3Ti particles that act as nucleation sites for the α-Mg phase. Furthermore, adding 1 wt.% Sr and 0.1 wt.% Ti enhanced the hardness values for both cast and aged AZ91 alloy. Moreover, ultimate tensile strength and tensile elongation values reached their maximum amounts with the 0.5 wt.% Sr and 0.1 wt.% Ti additions and more Sr and Ti additions deteriorated the mechanical properties of cast and aged AZ91 alloys. The fracture surface characterizations had good relations with the tensile properties. The fracture modes were cleavage and quasi-cleavage in the cast and aged AZ91 alloys. Furthermore, the optimum levels of Sr and Ti additions altered the fracture modes to more quasi-cleavage fractures.

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Authors and Affiliations

  1. School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran, Iran

    Aria Afsharnaderi, Mehdi Malekan, Massoud Emamy, Jafar Rasizadeh Ghani & Mehrab Lotfpour

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  1. Aria Afsharnaderi
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  2. Mehdi Malekan
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  3. Massoud Emamy
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  5. Mehrab Lotfpour
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Correspondence to Mehdi Malekan.

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Afsharnaderi, A., Malekan, M., Emamy, M. et al. Microstructure Evolution and Mechanical Properties of the AZ91 Magnesium Alloy with Sr and Ti Additions in the As-Cast and As-Aged Conditions. J. of Materi Eng and Perform 28, 6853–6863 (2019). https://doi.org/10.1007/s11665-019-04396-2

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  • DOI: https://doi.org/10.1007/s11665-019-04396-2

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