Influence of equal-channel angular extrusion on impact toughness of aluminum and brass at room and low temperatures

Background: Equal-channel angular extrusion is a severe plastic deformation process that can be used for grain refinement to improve material properties of bulk metals. In this paper, the effect of equal-channel angular extrusion on the impact toughness of aluminum 1100 and brass C26000 was investigated.Methods: Brass and aluminum materials were extruded in two and four passes using two equal-channel angular extrusion processing routes. Specimens were tested for hardness and Charpy impact toughness. Microstructure and fractography were examined.Results: The results showed the hardness remained almost constant after two passes for both brass and aluminum. Impact energy of brass after two passes decreased due to increase in dislocation density whereas for aluminum it remained almost constant after four passes due to the formation of ultrafine grains in addition to deformation/ dislocation structures. Impact energies of specimens tested at room temperature and low temperature (-70°C) were almost the same due to their face-centered crystal structure. It was also found that the impact toughness of a specimen with a non-distorted notch surface is higher than that of a specimen with a distorted notch surface.Conclusions: It is evident from the present study that the number of passes determines the extent of ultrafine grain structure that is known to increase impact toughness of equal-channel angular extrusion processed materials. All of these observed characteristics can influence material and process selections in practical design applications. © 2014 Wang et al.