Experimental and Diffusion Simulation for the Homogenization of As-cast Mg-Al, Mg-Zn, and Mg-Al-Zn Alloys
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RODUCTION
MAGNESIUM and magnesium based alloys are receiving global attention due to its superior light weight characteristics, especially in transport sector. The most common commercial Mg alloys are AZ (Al and Zn), ZA (Zn and Al), AM (Al and Mn), and AS (Al and Si) series which are used both as-cast and wrought products. Although the cast Mg products have been widely used in automotive and electronic applications, the commercialization of wrought Mg alloys is still slower than its potential because of their limited room temperature formability, low creep resistance, and inferior high temperature mechanical properties. Therefore, active research is being carried out to understand the deformation process and improve the formability of Mg alloys. The first process of wrought Mg production is typically the homogenization (solution treatment) of cast Mg product. The purpose of this process is to dissolve the second phase and homogenize as-cast microstructure as much as possible to provide optimum microstructure for subsequent rolling or extrusion process. The temperature and time for homogenization of Mg alloy are dependent on the as-cast microstructure which is varied with casting condition and alloy composition. Typical homogenization process for AZ alloys in industry is carried out at higher than 603 K (330 °C) for more than several hours.[1–3] The homogenization process is time consuming and requires high temperature, and hence optimization of the process is essential SAZOL KUMAR DAS, Ph.D. Student, and IN-HO JUNG, Associate Professor, are with the Department of Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5, Canada. Contact e-mail: [email protected] DAE-HOON KANG, formerly Post-Doctoral fellow with the Department of Mining and Materials Engineering, McGill University, is now Research Metallurgist with the Novelis Global Research and Technology Center, Kennesaw, GA 30144. Manuscript submitted January 23, 2014. Article published online July 11, 2014 5212—VOLUME 45A, OCTOBER 2014
for cost competition. Numerous experimental and modeling works have been performed by different researchers to optimize the homogenization process for AZ series alloys previously. Celotto and Bastow[4] performed NMR study with 27Al to observe the evolution of precipitates in binary Mg-Al and ternary Mg-AlZn alloys during aging. Dobrzanski et al.[5,6] performed experiments to determine heat treatment conditions for the ternary Mg-Al-Zn alloys and they also developed a neural network model to optimize the process parameters for heat treatment process. Zhu et al.[7] studied the dissolution of eutectic Mg17Al12 phase in as-cast AZ91 alloy at temperatures close to eutectic temperature. Vermolen et al.[8–11] have performed several numerical modelings to compute the dissolution of second phase in binary and ternary Mg alloys. Process parameters for heat treatment condition of Mg-based alloys can also be found in the ASM Handbook.[12] Recently, the present research group performed systematic casting experiments for Mg-Al
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