Measurements are reported on the steady-state ablation rates and surface temperatures of aluminium alloys 2024 and 7075 caused by a CW CO₂ laser assisted by a gas flow of variable composition. The effects of surface layers of oxides and nitrides on the absorptances at 10.6 mu m were investigated. Absorptances for these alloys were found to be substantially lower than those measured earlier for steels and titanium alloys.