This paper presents an extensive study of the structural, magnetic, and thermodynamic properties of the heterometallic ludwigite Co4.76Al1.24(O2BO3)2. This material orders ferrimagnetically at 57 K. Despite the fact that, in Co4.76Al1.24(O2BO3)2, one quarter of the Co ions of the parent compound Co3O2BO3 is replaced by nonmagnetic Al3+ ions, the TC of the former (57 K) is larger than that of the latter (42 K). We obtain the phase diagram of Co4.76Al1.24(O2BO3)2 in an external magnetic field. We find a line of second-order phase transitions where the system presents a metamagnetic transition (from 57 to 25 K). This line ends at a tricritical point at 25 K and 4.3 T, below which the transition to the paramagnetic phase is first order (from 25 to 3 K). In the magnetic phase at low temperatures specific heat measurements in zero and finite magnetic fields show that the low-energy excitations are magnetic (magnons) and elastic (phonons) excitations with two-dimensional character. These measurements also reveal the magnetocaloric properties of this material.