Microstructure, Tensile Properties and Fracture Behavior of HPDC Magnesium Alloy AZ91

Abstract—Understanding of tensile and fracture behaviours of die cast magnesium alloys is of importance for proper design of various emerging automotive applications. In the present study, magnesium alloy AZ91 was high pressure die cast into rectangular coupons with section thicknesses of 2, 6 and 10 mm. The effect of section thicknesses on strain-hardening and fracture behaviours of the die cast AZ91 was investigated. The results of tensile testing indicate that the ultimate tensile strength (UTS), yield strength (YS), elongation (ef), modulus, toughnrss and resilience decrease to 129.17, 110.59 MPa, 0.37%, 25.9 GPa, 0.89 MJ/m3 , and 236.10 kJ/m3 from 245.54, 169.26 MPa, 4.07%, 37.8 GPa, 8.34 MJ/m3 , and 378.95 kJ/m3 with increasing section thicknesses of die cast AZ91 to 10 mm from 2 mm, respectively. The analysis of true stress vs. strain curves shows that the straining hardening rates during the plastic deformation of the alloy increase to 5500 MPa from 4600 MPa with decreasing the section thickness to 2 mm from 10 mm, respectively. The microstructure analyses by the optical microscopy (OM) and scanning electron microscopy (SEM) reveal that the high tensile properties should be attributed the low porosity level, fine dendrite structure, high eutectic content, and thick skin. The observation via SEM fractography illustrates that the fracture behaviour of die cast AZ91 is influenced by section thicknesses. As the section thickness increases, the fracture of AZ91 tends to transit from ductile to brittle mode due to arising porosity content and coarsening microstructure.

Index Terms—Magnesium alloy AZ91, high pressure die casting, tensile and fracture behaviors, microstructure.

The authors are with Department of Mechanical, Automotive & Material Engineering, University of Windsor, Windsor, ON N9B 3P4 Canada (e-mail: sun13h@uwindsor.ca, gengx@uwindsor.ca, ren11h@uwindsor.ca, huh@uwindsor.ca).

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Cite: Zixi Sun, Xinyu Geng, Luyang Ren, and Henry Hu, "Microstructure, Tensile Properties and Fracture Behavior of HPDC Magnesium Alloy AZ91," International Journal of Materials, Mechanics and Manufacturing vol. 8, no. 2, pp. 50-56, 2020.

Copyright © 2020 by the authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).