Microstructure Modification of Powder Compact of Al-Zn-Mg Nanostructured Alloy by a Semisolid Thermomechanical Processing

A thermomechanical process (TMP) consisting of three cycles of cold pressing at 154 MPa and liquid-phase sintering at 600 °C for 30 min in each cycle was applied to modify the microstructure of nanostructured Al–Zn–Mg alloy. The alloy powders were produced by mechanical alloying. Also, solid-state sintering at 550 °C for 90 min was done to compare the results with those obtained from the TMP. The powders and the thermomechanically (TM) processed samples were analyzed by XRD to reveal the present phases in addition to calculating the crystallite size changes by the Williamson–Hall method. Moreover, scanning electron microscope was employed to observe the morphology of the powder and the microstructures of the sintered and the TM processed samples. The results revealed that the TMP affected the microstructure noticeably as well as the microhardness by removing the continuous grain boundary porosities and uniform distribution of the intermetallic phase particles as well as obtaining a near globular microstructure after the second cycle. Also, the average grain sizes in the first and the second cycles of the TMP were lower than those of the sintered sample. Furthermore, nanocrystalline grains were stable up to the second cycle of the TMP.