Microstructural analysis of AZ91D and AZ31B tested at high strain rates under tension

• Main Author: Koo, Teck Chee.
• Other Authors: Shu Dong Wei
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/49886
• Institution: Nanyang Technological University

Automobile and aerospace manufacturers are continuously looking for ways to reduce vehicle weight, thereby reducing the fuel consumption and emissions, and improving handling and safety. Two ways of accomplishing this goal are firstly to optimize the vehicle design so that unnecessary material is removed and to find applications where steel could be replaced with a less dense material such as aluminum. However, it was discovered that by using magnesium alloy instead of aluminum alloy, the density could be even reduced further up to two third that of aluminum without compromising other properties such as specific strength and corrosion resistance [1]. A lot of studies have been done to study the mechanical behavior of magnesium alloy to evaluate its mechanical properties such as its behavior at low and high strain rates, yield and ultimate tensile stress etc. However, it is important to study and analyze the effect of strain rates on the magnesium alloy at microstructural level as the effect of grain size and twins directly affects the corrosion behavior of the magnesium alloy [2]. In this project, the tensile specimens namely AZ31B and AZ91D were obtained from previous students that had conducted collision tests on the specimens in order to investigate their mechanical properties when subjected under low (Quasi-Static) and high (Dynamic) strain rates. The project consists of 2 stages namely; preparation of the tensile specimens (cutting, grinding, molding and surface polishing) and microstructure analysis using both the Optical Microscope (OM) and Scanning Electron Microscope (SEM). The analysis will illustrate the effect of strain rates on Tensile Microstructure Analysis i the tensile AZ31B and AZ91D magnesium alloy specimens at room temperature and the main deformation mechanisms involved. It is found that as strain rate increases for AZ31B rolling direction, twin increase significantly whereas for transverse direction, grains become finer with the absence of twins. For AZ91D, it is observed that the lamellar β phase becomes disordered and some micro – cracks observed in the bulk β and α phase.