There are certainly some aluminium frame bikes of CR interest. I have two French frames that surely qualify - a Pierre Collin from about 1939. In single fixed form it weighs under 15lb - the frame itself weighs 2.4lb. However I would not want to ride it often. The seatstays and chainstays are steel tubed size as are the forks which have an aluminium steerer. They deflect alarmingly during riding. The other frame is a Barras and is much better known especially in France where they are highly regarded. They are slightly heavier 3lb for a bare frame. They were imported into Britain in the early 50s by Fonteyn and have quite modern tubing shapes - plenty of taper and ovalised slightly oversized tubes. My Barras I think is post WWII but were made in France from around 1935 to 1956. I soon will have a ladies mixte Barras for sale from a deceased friend's collection. It is a welded frame made from what is a close match for 6061 tubing. The French in the know say that the survivors are quite reliable and good to ride. And of course one should not forget the Caminargent - octagonal tubing clamped in lugs. These are apparently pretty reliable - I have had one briefly in my possession and it appeared to pretty light and rather beautifully made. Caminargents were made both pre and post-WWII in France. Finally it should not be forgotten that Mercier built quite large quantities of aluminium framed bikes both utility and racing in the 40s and 50s. These survive quite well.
Hilary Stone