Characteristics of Al-Zn-Mg-Cu Alloys with Nickel Additives Synthesized via Mechanical Alloying, Cold Compaction, and Heat Treatment

Mechanical alloying was employed to synthesize Al-Zn-Mg-Cu alloys with nickel additives from elemental powders via high-energy ball milling. The milled powders were cold compacted and sintered thereafter. The sintered compacts underwent homogenization treatments at various temperature conditions and aged at 120 A degrees C for 24 h (T6). Subsequently, the compacts were retrogressed at 180 A degrees C for 30 min and re-aged at 120 A degrees C for 24 h (RRA). The milled powders and heat-treated products were characterized via X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive spectroscopy. The crystallite sizes and micro-strains of the alloy powder were estimated with the broadening of XRD peaks by using the Williamson-Hall equation. The results show that Zn, Mg, and Cu atoms are soluble in the Al matrix after milling for 5 h. The Vickers hardness of Al alloys was enhanced following retrogression and re-aging treatments. The addition of nickel influenced the hardness of the compacted powders.