Influence of strain rate on deformation behaviour of an AX52 alloy processed by equal channel angular pressing (ECAP)
Abstract
Cast AX52 magnesium alloy with Al and Ca was processed by equal channel angular pressing (ECAP) using A route and 1-8 passes. The light and electron microscopy revealed a substantial microstructure refinement in the alloy.
Al2Ca eutectics were found to be typical features of the microstructure. The ECAP procedure disintegrated eutectic particles.
Miniaturized samples were cut from the ECAP-processed bulks. The samples with the tensile axis parallel to the extrusion direction were tested in tension at room temperature with initial strain rates of 0.001, 1, 10 and 50 s(-1).
The offset yield stress increased with increasing number of passes. A rapid increase of deformation stresses was observed for the highest strain rate of 50 s-1.
The activation volumes were estimated from the strain rate dependence of the offset yield stress. The strain rate sensitivity is influenced by the number of passes.
A rapid increase of the activation volume at the highest strain rate indicates the change of the deformation mechanism. Limiting small values of the activation volume were found for the highest strain rates.
Tensile tests at higher strain rates revealed unstable deformation behavior. This unstable deformation depends on the number of passes.
Mechanisms operating at various strain rates are discussed in relation to the microstructure and number of ECAP passes.