The UFe_xAl_12−x series was the object of a systematic experimental study in single crystals with different compositions [Phys.Rev. B 60, 9494 (1999)]. Several experimental technics were used to suggest a magnetic phase diagram of the system. Three different ranges of composition were found to have different magnetic behaviour: x < 4+δ₁, 4+δ₁ < x < 5-δ₂, and x > 5-δ₂. Here δ₁ and δ₂ are small positive numbers The UFe₄Al₈ and UFe₅Al₇ compounds belong to two different regions of the phase diagram. DFT calculations and symmetry analysis of these two compounds [Phys.Rev. B 60, R6961 (1999); 65, 94413 (2002)] contributed to the understanding of the origin of the complex magnetic behaviour of the series. In order to complete the systematic study of the series we report calculations of magnetic properties for UFe_4.5Al_7.5. The latter compound belongs to the third and the most interesting region of the phase diagram with two magnetic phase transitions. Based on this ab inition study, we discuss the proposed phase diagram.