OPTIMIZATION OF ANNEALING DURATION FOR ENHANCED MICROSTRUCTURE AND PROPERTIES IN A Zn-2.4Mn ALLOY

Kar Fei Chan; Ng Cong Li; Batrisyia Balqis; Yazid Yaakob; Hidetoshi Miyazaki; Masaki Tanemura; Mohd Zamri Mohd Yusop

Kar Fei Chan Department of Materials, Manufacturing and Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.
Ng Cong Li Department of Materials, Manufacturing and Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia
Batrisyia Balqis Department of Materials, Manufacturing and Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.
Yazid Yaakob Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia.
Hidetoshi Miyazaki Department of Physical Science and Engineering, Nagoya Institute of Technology, 466-8555 Nagoya, Aichi, Japan.
Masaki Tanemura Department of Physical Science and Engineering, Nagoya Institute of Technology, 466-8555 Nagoya, Aichi, Japan.
Mohd Zamri Mohd Yusop Department of Materials, Manufacturing and Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.

Keywords: Zn-Mn alloy, plastic deformation, Vickers hardness, heat-treatment process, metallurgy

Abstract

This study investigates the microstructural evolution and mechanical response of a Zn-2.4Mn alloy subjected to controlled heat treatments. The alloy was evaluated in as-cast, homogenised (390 °C), and annealed states (400 °C for 1-4 h) using optical microscopy, grain segmentation, Vickers hardness, tensile testing, and indentation cross-section analysis. The as-cast Zn-2.4Mn exhibited coarse dendritic grains with significant Mn segregation (grain area 5416.55 µm²) and poor mechanical properties: UTS of 28.33 MPa and elongation of
2.84 %. Homogenisation reduced chemical gradients but increased measured grain area to 6834.19 µm² due to dissolution of fine dendritic boundaries, while UTS improved to 102.06 MPa and elongation to 6.10 %. Recrystallisation initiated after 1 h of annealing (grain area 4684.46 µm²; UTS 103.38 MPa; elongation 4.38 %) and progressed to full refinement by 3 h, producing the minimum grain area of 3263.32 µm². Hardness increased from 53.12 HV (as-cast) to 73.13 HV at 3 h, while tensile performance reached its optimum (UTS 152.92 MPa, elongation 7.31 %). Indentation analysis confirmed the 3 h condition produced the most uniform deformation profile. Prolonged annealing to 4 h resulted in grain coarsening (4168.23 µm²), decreasing UTS to 113.25 MPa and elongation to 4.59 %, while hardness increased slightly to 74.73 HV, suggesting supplementary strengthening from residual MnZn₁₃ precipitates. These results demonstrate that annealing at 400 °C for 3 h provides the optimal balance of grain refinement, strength, and ductility for the Zn-2.4Mn alloy, establishing a clear processing–microstructure–property relationship.