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Hot workability and microstructure evolution of Al–0.2Sc–0.04Zr alloy

Xue, Yong, Chen, Shuaishuai, Zhang, Zhimin, Wang, Qiang, Yan, Jiangpeng
Journal of materials science 2019 v.54 no.10 pp. 7908-7921
alloys, aluminum, crystallization, deformation, microstructure, prediction, temperature
Hot deformation behavior of Al–0.2Sc–0.04Zr (wt.%) aluminum alloy was investigated via conducting hot compression tests at temperatures of 440–600 °C and at strain rates, ranging from 0.001 to 5 s⁻¹, at an interval of an order of magnitude. The characteristics of the true stress–strains acquired in the hot compression tests were investigated, and the influence of processing parameters on the microstructure of the deformed samples was observed by using optical microscope and electron back-scattered diffraction (EBSD). Two types of processing maps for Al–0.2Sc–0.04Zr alloy were developed using the Kumar–Prasad (K–P) and Murty–Rao (M–R) instability/stability criteria, respectively. The prediction results of two types of processing maps were examined. Based on the analysis of the M–R processing map and EBSD, a deformation mechanism map covering a wide range of temperature and strain rate was developed. The result shows that the flow stress had a rapid increase to the maximum stress, and subsequently, the flow stress decreases continually to be of steady-state type when the deformation continues on. The M–R criterion can more accurately predict the unstable region than the K–P criterion. The optimum temperature T and strain rate [Formula: see text] combination conditions for Al–0.2Sc–0.04Zr alloy are T = 520–560 °C, [Formula: see text] = 10⁻³ s⁻¹ or [Formula: see text] = 0.1–5 s⁻¹. The microstructure evolution dominated by the predominant or complete dynamic recrystallization can be acquired by deformation at the combination conditions. However, it is dominated mainly by dynamic recovery at lower temperatures (T < 520 °C) and by dynamic recrystallization at higher temperatures (T > 520 °C). In addition, the microstructure of specimen deformed at 600 °C shows a growing and coarse trend. Moreover, the nano-dimension precipitate particles of Al₃(Sc,Zr) are uniformly distributed throughout Al matrix. The efficiency parameter η value of Al–0.2Sc–0.04Zr alloy in processing maps is smaller in comparison with that in pure aluminum, and it could be attributed to these nano-dimension particles.