Texture, microstructure and mechanical properties of AA7075-graphite composites produced through mechanical alloying and hot-extrusion

This paper reports the effect of graphite and milling time on the texture, microstructure and mechanical properties of AA7075-graphite composites produced through mechanical alloying and hot extrusion. Characterization was conducted by scanning electron microcopy, transmission electron microscopy, X-ray diffraction, laser diffraction, electron backscatter diffraction and precession electron diffraction, and mechanical properties were evaluated by uniaxial tensile tests. Results show that particle and crystallite size of mechanically milled powders affect the grain size of extruded samples. Most of extruded samples exhibit deformation textures components, however, in-grain misorientation values were lower than 2°, which is an indicative of their recrystallization. The presence of deformation texture components in recrystallized samples is explained by the oriented nucleation mechanism. Hardness, yield strength (YS) and ultimate tensile strength increase, while elongation to fracture decreases, with the increase in graphite content and milling time. The size of recrystallized grains decreases with the increase in milling time and graphite content. Furthermore, YS varies with grain size according to the Hall-Petch relationship. Hardening of the investigated AA7075-graphite composites is enhanced by grain refinement, dispersion of Al₄C₃, Mg₂Zn₂ and Al₂O₃; and to a lesser extent by the random texture developed.