Superplastic Deformation Mechanism of an Ultrafine-grained Aluminum Alloy Produced by Friction Stir Processing


An ultrafine-grained (UFG) Al-4Mg-1Zr alloy with a grain size of ∼0.7 µm with predominantly high-angle boundaries of 97% was produced by friction stir processing (FSP). The UFG Al-4Mg-1Zr retained submicrometer grains even after static annealing at 425 °C, and exhibited excellent superplasticity at 175-425 °C. High strain rate and low-temperature superplasticity of > 1200% were observed at 1 × 10-2-1 × 10-1 s-1 and 300-350 °C. Even at 425 °C, a superplasticity of 1400% was achieved at 1 s-1. A linear relationship between logover(ε, ̇)opti and T was observed (where over(ε, ̇)opti is the optimum strain rate, and T is the temperature). The analyses on the superplastic data revealed the presence of threshold stress, a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy of 142 kJ mol-1. This indicated that the dominant deformation mechanism was grain boundary sliding, which was controlled by lattice diffusion. Based on this notion, a constitutive equation has been developed. A new superplastic deformation mechanism map for FSP aluminum alloys is proposed.




Hundred Talents Program of Chinese Academy of Sciences
National Natural Science Foundation (China)
National Outstanding Young Scientist Foundation of China
National Science Foundation (U.S.)

Keywords and Phrases

Dominant Deformation Mechanism; Friction Stir Processing; Grain Size; High Angle Boundaries; High Strain Rates; Inverse Grain Size; Lattice Diffusion; Linear Relationships; Low Temperature Superplasticity; Static Annealing; Stress Exponents; Submicrometers; Superplastic Deformation Mechanisms; Threshold Stress; Ultra Fine Grained Microstructure; Ultrafine-grained; Activation Energy; Aluminum; Aluminum Alloys; Aluminum Metallurgy; Friction; Grain Boundaries; Grain Boundary Sliding; Grain Size And Shape; Microstructure; Superplastic Deformation; Superplasticity; Tribology; Zirconium; Strain Rate

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© 2010 Elsevier, All rights reserved.

Publication Date

01 Aug 2010