Effect of the Fe/Mn Ratio on the Microstructural Evolution of the AA6063 Alloy with Homogenization Heat Treatment Interruption

Abstract

The casting structure of the AA6063 alloy contains intermetallic particles of β-Al5FeSi, which can result in the fragility of the cast pieces. However, with heat treatment, the β phase transforms from a needle or plate form into an intermetallic phase known as α, which resembles Chinese-script in its morphology. To analyze the effect of the ratio of Fe/Mn with different ratios of 0.5, 0.75, and 1, a heat treatment process is used with intermittent interruptions. The alloy is subjected to a temperature of 575 °C for 12 h to determine the microstructural evolution of the β-Al6FeMn and α-Al15(FeMn)3Si2 phases. This study used scanning electron microscopy to conduct point analyses and elemental mappings of the intermetallics found in the casting and heat treatment samples. Additionally, X-ray diffraction was employed to determine the stoichiometry of the present phases. The results indicated that the cast structure contains β-Al6FeMn and α-Al15(FeMn)3Si2 phases and that the β-Al6FeMn phase transforms into the α-Al15(FeMn)3Si2 phase upon completion of the heat treatment process. By using specific Fe/Mn ratios, the formation of the needle-shaped Al5FeSi phase in the casting structure of the alloy can be inhibited, leading to the precipitation of phases such as β-Al6FeMn and α-Al15(FeMn)3Si2 instead.