Influence of In-Plane Pre-Compression and Ageing Heat Treatment on the Anisotropic Behaviour and Mechanical Properties of AZ31B Alloy

Due to its low mass density and high strength-to-weight ratio, magnesium alloys are the prime candidates over steel and aluminium in weight-saving applications like aerospace and automobile industries. However, the hexagonal close-packed (HCP) crystal structure limits its wide usage due to fewer slip systems and inherent anisotropy at ambient conditions. Therefore, an improvement in their anisotropic and mechanical properties is highly needed for sheet metal forming applications. Recently, the in-plane pre-compression technique provided a new strategy for enhancing the forming behaviour of Mg alloys by introducing twins in their microstructure. The microstructure and mechanical properties of AZ31B alloy have been studied in the present work. A special die is developed to prevent sheet buckling during pre-compression. The as-received sheets of 120 mm (RD) x 120 mm (TD) x 1mm (ND) dimension are used, and a pre-compression strain of 1.6 % is induced along RD. The compressed sheets were aged at 170°C for 16 hours. The microstructure of the aged sheet is analyzed using the electron back-scattered diffraction (EBSD) technique. The result reveals that the crystallographic basal texture is significantly weakened with pre-compression. After ageing, the uniaxial tension is conducted at ambient temperature and a strain rate of 0.001s ‐1 . There was a 34.42% reduction in the yield strength, while the ultimate tensile strength remained nearly unchanged. The pre-compressed Mg sheet increased the strain hardening exponent from 0.125 to 0.314, along with a decrease in normal anisotropy from 3.003 to 1.131, both of which contribute to improved forming capacity.