Improving ductility of bimodal carbon nanotube/2009Al composites by optimizing coarse grain microstructure via hot extrusion

Bimodal carbon nanotube reinforced 2009Al (CNT/2009Al) composites were fabricated by powder metallurgy followed with extrusion. It indicated that the width, length and grain size in the coarse grain (CG) bands increased with the increase of the extrusion temperature, while no obvious grain size change was observed in the ultra-fine grain zones. The bimodal composite showed a double yield phenomenon. The first yield strength which resulted from the yielding of the CG, was similar for all composites extruded with different temperatures. The second yield strength decreased, but the ultimate tensile strength retained stable and the elongation increased with increasing the extrusion temperature. The composite extruded at 470 degrees C exhibited a 76% ductility increase with nearly no ultimate tensile strength loss as compared to one extruded at 370 degrees C. The better stress relaxation ability of large-sized grains in the CG bands was believed to be the reason for the good strength-ductility.