Microstructural Evolution and Kinetics of 7075 Al Alloy During Homogenization Treatment

Homogenization treatment reduces elemental microsegregation and promotes homogeneous solute distribution, thereby enhancing microstructural homogeneity and mechanical properties. This study employed optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and Vickers microhardness tester to systematically investigate the microstructural evolution, compositional distribution and microhardness of as-cast 7075 Al alloy during homogenization. Significant dendritic microsegregation was observed in the as-cast alloy, particularly with Cu, Mg and Zn concentrated along grain boundaries and dendritic cores. As homogenization temperature and holding times increased, dendritic structures gradually diminished, and non-equilibrium phases dissolved into the matrix. At 465°C for 24 h, the second-phase area decreased from 6.67% to 1.58%, and the grain boundary width reduced from 4.47 μm to 2.29 μm. After further homogenization at 475°C for 4 h, the grain boundary width is approximately 0.68 μm, and the area fraction of the second phase is only 0.65%. Initially, the dissolution of low-melting non-equilibrium phases decreases microhardness. Longer homogenization and cooling processes cause phase transformations, slightly increasing and stabilizing hardness. The optimal double-stage homogenization treatment achieved a homogeneous microstructure. Diffusion kinetics during homogenization revealed that the redistribution of alloying elements, driven by atomic diffusion, effectively reduces elemental microsegregation and optimizes processing parameters.