Effects of Cr addition on the microstructure and mechanical behavior of 6061-T6 continuously cast and rolled redraw rod

Chromium additions to 6061 aluminum alloy can form α-Al12(Fe, Cr)3Si dispersoids during homogenization. Continuous cast bar does not receive a homogenization step and is rolled directly after casting, therefore, it is of interest to determine the effect of Cr addition on the microstructure and mechanical properties of continuous cast 6061-T6 rod. Microstructural examination of 0.5 inch diameter continuous cast and rolled 6061 w/Cr T6 rod revealed that the rod had a fully recrystallized microstructure with pancake-shaped grains indicative of aluminum alloys containing dispersoids. Examination of TEM samples confirmed the existence of α-Al12(Fe, Cr)3Si dispersoids in the T6 rod microstructure. X-ray diffraction (Guinier techiique) revealed that the 6061 w/Cr T6 rod contained α-Al12Fe3Si and α-Al12(Fe, Cr)3Si constituent phases whereas the 6061-T6 rod without Cr contained only β-Al9Fe2Si2. Tensile test results showed that Cr addition to 6061-T6 rod substantially improved the ductility of the rod.