Low temperature quasi-superplasticity of ZK60 alloy
prepared by reciprocating extrusion
prepared by reciprocating extrusion
(1. School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China;
2. School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China)
2. School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China)
Abstract: Fine-grained ZK60 alloy was prepared by 2-pass reciprocating extrusion, and the low temperature superplasticity was conducted in a temperature range from 443 to 523 K and an initial strain rate ranging from 3.3´10−4 to 3.3´10−2 s−1. The results show that the alloy has an equiaxed grain structure with an average grain size of about 5.0 mm, and the sizes of broken secondary particles and precipitates are no more than 175 and 50 nm, respectively. The alloy exhibits quasi-superplasticity with a maximum elongation of 270% at 523 K and an initial strain rate of 3.3´10−4 s−1. The strain rate sensitivity m is less than 0.2 at 443 and 473 K, and it is 0.42 at 523 K. The apparent activation energies at temperature below 473 K and at 523 K are less than 63.2 and 110.6 kJ/mol, respectively. At temperature below 473 K, mainly intragranular sliding contributes to superplastic flow. At 523 K, grain boundary sliding is the dominant deformation mechanism, and dislocation creep controlled by grain boundary diffusion is considered to be the main accommodation mechanism.
Key words: ZK60 Mg alloy; reciprocating extrusion; quasi-superplasticity; intragranular sliding; grain boundary sliding