Homogenizing annealing heat treatment effects on the microstructure, hardness and thermal behavior of Al_(12)Mg_(17) complex metallic alloy

摘要

Microstructural evolutions, hardness and thermal behavior of Al_(12)Mg_(17) complex metallic alloy (CMA) were studied before and after homogenizing annealing. This heat treatment was conducted on the as-cast alloy at high temperature of 400 ℃ in different times in order to clarify the mechanism and also determining the optimum annealing time for achieving a single phase intermetallic compound. The as-cast microstructures involve γ-Al_(12)Mg_(17) and small amount of Mg-rich microsegregated phase which forms during eutectic solidification. Phase and microstructural evolutions during homogenization were comprehensively investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction patterns (XRD). The thermal behavior and hardness of the as-cast and homogenized intermetallics have been investigated by differential scanning calorime-try (DSC) and Vickers microhardness measurements, respectively. The results of these investigations indicated that homogenization treatment resulted in a diffusion of Mg from Mg-rich domains in eutectic structure to the intermetallic matrix, leading to evolution and dissolution of second phase along with the formation of Kirkendall porosities according to proposed mechanism. Finally a single phase of Al_(12)Mg_(17) CMA with higher lattice parameter, hardness and melting point formed after 32 h of homogenizing annealing heat treatment.