Acta Metall. Sin.(Engl. Lett.)Vol.22 No.6 pp401-407 December 2009 Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy H. Jafari 1,2) ∗ , M.H. Idris 1) , A. Ourdjini 1) and G. Payganeh 2) 1) Department of Materials Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Malaysia 2) Department of Materials Engineering, Faculty of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran, 16785-136, Iran Manuscript received 12 March 2009; in revised form 30 June 2009 Due to their high specific strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two different thermomechanical treatments (TMTs). For the first TMT, after solution treated at the temperature of 380 ◦ C for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ◦ C and 250 ◦ C for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ◦ C for 20 h, underwent 2% cold worked and quenched in water of 0 ◦ C. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ◦ C and 250 ◦ C for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of fine β-phase (Mg 17 Al 12 ) in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ◦ C whereas, in the second TMT, aging at 250 ◦ C exhibited the best hardness values. KEY WORDS Thermomechanical treatment; Magnesium alloys; Cold work; Aging; AZ63 1 Introduction In recent years, due to technological developments and concern on efficient usage of energy, magnesium alloys have attracted significant interest to be used in many applica- tions. This is due to its excellent advantages such as low density and cost and abundant supply [1] , high strength-to-weight ratio [2,3] , high damping capacity, dimensional stability, good machinability and recyclability [4] . The usage of magnesium alloys is increasing in industries including automotive [5−10] , transportation, aerospace, microelectronics, power- tools and new energy sources [1,4] . However, on account of its poor ductility [6,9] and due ∗ Corresponding author. PhD candidate; Tel.: +60 177790093. E-mail address: jafari − h@yahoo.com (H. Jafari) DOI: 10.1016/S1006-7191(08)60115-5