On the effect of non-isothermal annealing and multi-directional forging on the microstructural evolutions and correlated mechanical and electrical characteristics of hot-deformed Al-Mg alloy

Abstract

Specimens of hot-extruded AA5056-H38 aluminum alloy were subjected to multi-directional forging (MDF) and non-isothermal annealing. The combined effects of imposed strain and post-annealing on the microstructural evolutions, mechanical properties and electrical conductivity were investigated. Optical microscopy observations showed that consecutive passes of MDF resulted in grain refinement and non-uniform strain distribution created lamellar structure right after the second pass. According to the SEM micrographs, increasing the processing strain led to severe fragmentation of initial coarse intermetallic particles into ultrafine dispersoids and redistributed them within matrix. Meanwhile, during the annealing stage, recrystallization started from stress concentrated locations while asymmetric strain distribution eventually caused bimodal microstructure. Mechanical properties were evaluated using hardness and shear punch tests since results were in good agreement with microstructure transformations. Four-point probe electrical resistivity test outputs indicated that electrical conductivity had inverse relationship with dislocations density and grain boundaries volume.