I my TL, I am industrializing Kamerun, which has no coal but abundant hydroelectric, so I am going to look into this as the TL progresses. But I have very odd situation where many hundreds of millions of marks were spent on industrial infrastructure in a region with no coal. But since you can also make steel with electricity, I will probably not use aluminum in APC. Frames for airplanes, small river patrol boats, unarmored trucks, maybe few hundred ton ocean going boats, but APC looks like a real stretch. Aluminium production was taking off as the true big dams began to be built in the 1920's, and you can using Oregon and Washington state as an example. Once you have economic production of Aluminium, then you can think about someone funding the welding and other support technologies.
Are you trying to write a TL or something?