Influence of strain rate on hot deformation behaviour and texture evolution of AZ31B M. Sanjari* 1 , S. A. Farzadfar 1 , I. H. Jung 1 , E. Essadiqi 2 and S. Yue 1 In the present work, the effects of strain rate on the flow behaviour and microstructure evolution of AZ31 Mg alloy were studied by compression testing over a wide range of strain rates (0?01– 100 s 21 ) and temperatures (300–450uC). In addition, the influence of different strain rates on the dynamic recrystallisation (DRX) mechanisms and texture evolution was investigated. The results showed that with increasing strain rate, the twin induced DRX fraction increased at a constant temperature, and the contribution of continuous DRX decreased. On increasing the strain rate, the formation of twins and subsequent twin induced DRX intensified the basal texture in the deformed sample. In addition, the recrystallised volume fraction increased significantly with strain rate. The flow behaviour was fitted to two types of constitutive equations: power law and hyperbolic sine. Average activation energies of about 162 and 135 kJ mol 21 were obtained for the peak and steady state strain respectively. Keywords: High strain rate deformation, Texture evolution, Microstructure evolution, Constitutive behaviour, Recrystallisation mechanisms Introduction Of all the industrially significant metals and alloys, magnesium has the lowest density, which makes it a very attractive candidate for applications such as automotive, railway and aerospace industries. 1,2 However, magnesium and its alloys generally exhibit low ductility due to the limitations of the deformation mechanisms. 3 Therefore, it is necessary to improve the deformability of magnesium using secondary manufacturing processes such as rolling and extrusion. 1,4 To optimise the processing for plastic forming, it is important to understand the effect of temperature and strain rate on flow behaviour and microstructure evolution. To date, the effect of tempera- ture on the flow behaviour and deformation mechanism of magnesium alloy has been extensively investigated. 3,5–7 However, the effect of strain rate, especially high strain rates of .1s 21 , at which most secondary forming processes are performed, has rarely been examined systematically. A study by Lee et al. 8 on the effect of strain rates from 0?01 to 10 s 21 to a strain of 0?1 showed that the twinning fraction increases with increasing strain rate at 573 K. Essadiqi et al. 9 also studied the effect of high strain deformation using a cam plastometer. They found that with increasing strain rate, for a given strain, the recrystallised grain size becomes finer, and the strain triggering dynamic recrystallisation (DRX) increases. Ishikawa et al. 10 studied the high temperature compres- sive properties in AZ31 magnesium alloy over a wide strain rate range. Their analysis indicated that the deformation at high strain rates of 10 3 s 21 proceeds by dislocation glide and twinning. The latter was observed even at elevated temperatures. The goal of the present study is to investigate the high temperature deformation behaviour of AZ31 alloy by compression tests over the strain rate range from 10 22 to 10 2 s 21 with the aim of determining the influence of strain rate on the flow behaviour, microstructure and texture evolution. Detailed microstructure and texture examination by electron backscattered diffraction (EBSD) were carried out in selected samples in order to clarify the pre- dominant deformation and recrystallisation mechanisms at different strain rates. Experimental The present study was carried out on an AZ31B alloy with the following chemical composition Mg–3Al– 0?9Zn–0?67Mn (wt-%). < The as cast material was homogenised at 450uC for 4 h, which was found to give a consistent hot deformation behaviour. 9 This resulted in a coarse grain size of y200 mm measured by image analysis. To investigate the effect of strain rate on the microstructure and texture evolution, two series of tests were performed on the material in the temperature range from 300 to 450uC. In order to apply low strain rates (0?01 and 1 s 21 ), a computer controlled servohydraulic material testing system with a 100 kN capacity was used. The specimens were deformed to strains of about 0?3 and 0?7 to observe the effect of strain on the microstructure. For higher strain rates, a cam plast- ometer was used, which is a reliable method for determining the dynamic behaviour at strain rates on Materials Science and Technology mst9902.3d 24/8/11 11:12:52 The Charlesworth Group, Wakefield +44(0)1924 369598 - Rev 7.51n/W (Jan 20 2003) 1 Department of Materials Engineering, McGill University, Montreal, Que. H3A 2B2, Canada 2 CANMET – Materials Technology Laboratory, Ottawa, Ont. K1A 0G1, Canada *Corresponding author, email mehdi.sanjari@mail.mcgill.ca ß 2011 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 24 June 2011; accepted 30 July 2011 DOI 10.1179/1743284711Y.0000000080 Materials Science and Technology 2011 VOL 000 NO 000 1