Magnesium nuclei in cosmic rays are mainly produced and accelerated in astrophysical sources. While Aluminum nuclei are produced both in astrophysical sources and by the collisions of heavier nuclei with the interstellar medium. Knowledge of the precise behavior of their spectrum are important in understanding the origin, acceleration, and propagation processes of cosmic rays in the Galaxy. The surviving fractions of the radionuclides Be-10 and Al-26 provide information on the cosmic-ray residence time. The surviving fraction of Al-26 can be extracted by the Aluminum-to-Magnesium flux ratio providing information on the energy dependence of the residence time. The precision measurements of Mg and Al fluxes in the rigidity range from 2.15GV to 3.0TV based on data collected by the Alpha Magnetic Spectrometer during its first 8.5 years of operation are presented. A feasibility study of extracting the Be-10 and Al-26 surviving fractions from Be/B and Al/Mg flux ratios is also discussed.