Magnetic garnets such as yttrium iron garnet (Y3Fe5O12, YIG) are widely used in spintronic and magnonic devices. Their magnetic and magneto-optical properties can be modified over a wide range by tailoring their chemical composition. Here, we report the successful growth of Al-substituted yttrium iron garnet (YAlIG) thin films via radio frequency sputtering in combination with an ex situ annealing step. Upon selecting appropriate process parameters, we obtain highly crystalline YAlIG films with different Al3+ substitution levels on both single crystalline Y3Al5O12 (YAG) and Gd3Ga5O12 (GGG) substrates. With increasing Al3+ substitution levels, we observe a reduction of the saturation magnetization as well as a systematic decrease of the magnetic ordering temperature to values well below room temperature. YAlIG thin films thus provide an interesting material platform for spintronic and magnonic experiments in different magnetic phases.