Microstructural characterization of nanostructured Al-Zn-Mg-Cu alloy during mechanical alloying and subsequent annealing

In this study, Al-6Zn-2.5Mg-1.5Cu alloy powders were synthesized by mechanical alloying of the elemental powders of Al, Zn, Mg and Cu at different milling times. The 60 h milled powders were isothermally annealed at 380 degrees C for 30 min under argon atmosphere. The microstructure and mechanical properties of the as-milled and annealed powders were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness test. The crystallite size and lattice strain of Al were estimated from the broadening of XRD peaks using Williamson-Hall method. The results showed that the crystallite size of Al decreases with increasing milling time and after milling up to 60 h, the crystallite size reduced to 76 nm. Due to formation of intermetallic phases such as MgZn2 during annealing, an increase in the hardness of the alloy powders was achieved.