How to prevent Ag2O from decomposing to Ag on Aluminum
First,  as you mention, $\ce{Ag2O}$ starts to decomposes from ≥200 °C. Measure the temperature of the aluminum substrate with an IR thermometer or attached thermocouple to be sure you stay well below that. You can substantially speed drying of the ink by lowering the air pressure, e.g. using an aspirator pump, perhaps eliminating need to heat the substrate.

You may also need to anodize the aluminum prior to printing  to prevent chemical reaction with the $\ce{Ag2O}$ in the ink. Aluminum is much higher in the electromotive series and would rapidly replace silver in the oxide.