Diffusive transformation at high strain rate: On instantaneous dissolution of precipitates in aluminum alloy during adia
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Shuhong Luo School of Material Science and Engineering, Central South University, Changsha, 410083, China
Haibo Hu and Tiegang Tang Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, 621900, China
Qingming Zhang State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, 100081, China (Received 6 November 2015; accepted 28 March 2016)
Dynamic loading of the hat-shaped specimen of 2195-T6 aluminum lithium alloy was carried out with a split Hopkinson pressure bar at ambient temperature. The formation and evolution mechanisms of adiabatic shear band (ASB) in this alloy were investigated and then microstructure was further observed. The microstructure within ASB in 2195 aluminum alloy was characterized by means of optical microscopy and transmission electron microscopy. The width of ASB was about 20–30 um. Nano-grains (50–100 nm) were observed in the middle of shear zone. Experimental results show that the diffusive transformation took place within ASB during high strain rate deformation, namely the precipitates dissolving in the matrix in the process (within about 71 ls). Based on thermodynamics and kinetics analyses, dissolution of precipitates was firstly investigated during adiabatic shearing deformation, and a dissolution model was suggested in the present work. The diffusive transformation and the microstructure evolution within ASB in 2195 alloy were explained.
I. INTRODUCTION
Adiabatic shearing is a common form of localized plastic deformation of material under high strain rate loading such as: high speed impact, penetration, erosion, high speed cutting, high speed molding, and explosive cladding.1–3 At present, due to the limited time for diffusion (in microseconds), the phase transformation under high-strain-rate loading is generally considered to be nondiffusive transformation such as martensitic transformation.4,5 Yuan6 investigated the formation and evolution mechanisms of adiabatic shear band (ASB) in 0.2C5Mn steel and found the fraction of austenite phase is decreased and almost disappeared due to martensitic transformation. And the martensitic transformation was
observed in the ASB in several materials such as 304 stainless steel,7 and titanium alloy.8–10 Based on our previous work,11 the precipitates of 2195-T6 aluminum lithium alloy were dissolved instantly in matrix which further confirmed that the diffusive phase transformation took place during adiabatic shearing. According to the phenomenon of instantaneous dissolution of precipitates in the adiabatic shear zone, the thermodynamics, dynamics, and dissolving mechanism of the instantaneous dissolution of precipitates during adiabatic shearing were firstly discussed in the present work.
II. EXPERIMENT
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.151
The 2195 aviation aluminum lithium alloy (Al–4.0Cu– 1.0Li–0.4Mg–0.4Ag–0.12Zr, wt%) was used in this investigation. The as-received material was pre
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