You can rub a little autosol on it and use a soft cloth to wipe it off. Try using those cloths usually sold for washing cars.

Do not rub the autosol too hard onto the aluminium frame if you're worried about scratching. Try at the bottom of the frame in an inconspicuous corner for whether the solution here fits your needs before doing the whole frame.

Polishing it would help a little if the scratch is not too deep.