Processing of long ultrafine-grained AM60 magnesium alloy tube by hydrostatic tube cyclic expansion extrusion (HTCEE) under high fluid pressure

Abstract

In this study, hydrostatic tube cyclic expansion extrusion (HTCEE) at elevated temperatures was utilized to produce relatively long ultrafine-grained (UFG) AM60 magnesium alloy tubes. HTCEE method is able to apply large strains to tubular parts and produce long UFG tubes without changing their dimensions due to the reduction of the friction at interfaces using high-pressure molten polymeric fluid at an elevated temperature. This method is performed on an AM60 magnesium alloy at an elevated temperature of 300 °C, and the microstructure and mechanical properties were examined. The results represent a significant enhancement of the mechanical properties and a dramatic reduction in the grain size. The yield and ultimate strength were increased to 160 MPa and 328 MPa after first passes of HTCEE from the primary values of 130 MPa and 212 MPa; also the elongation to failure increased to 31% from 9%. Microhardness was increased to about 72 Hv after the HTCEE process from the primary value of 50 Hv. Microstructural results showed a significant grain refinement to a grain size of ~ 3 μm after the process from the primary value of ~ 160 μm. Finite element results exhibit a very significant (~ 85% reduction) decrease in the required load and increase in the strain homogeneity in the HTCEE process compared to its conventional counterpart. This method seems to be very promising for future industrial applications.