Mechanical and Microstructural Properties of Ultra-fine Grained AZ91 Magnesium Alloy Tubes Processed via Multi Pass Tubular Channel Angular Pressing (TCAP)

Ultra-fine grained (UFG) cylindrical tubes were produced via recently developed tubular channel angular pressing (TCAP) process through different passes from as-cast AZ91 magnesium alloy. The microstructure and mechanical properties of processed tube through one to four passes of TCAP process at 200 degrees C were investigated. Microhardness of the processed tube was increased to 98.5 HV after one pass from an initial value of 67 HV. An increase in the number of passes from one to higher number of passes has no more effect on the microhardness. Yield and ultimate strengths were increased by 4.3 and 1.4 times compared to those in as-cast condition. Notable increase in the strength was achieved after one pass of TCAP while higher number of passes has no more effect. Microstructural investigation shows notable decrease in the grain size to around 500 nm from the primary value of similar to 150 mu m. Dissolution and distribution of hard Mg17Al12 phase in the grain boundaries of dynamically recrystallized UFG AZ91 with a mean grain size of similar to 500 mu m was an interesting issue of TCAP processing at 200 degrees C compared to other severe plastic deformation processes.