Coat the aluminium in melted candlewax and it will come out with some boiling water quite easily. Alternatively you can make a single cut the length of the tube nd insert a flat bar the width of the saw cut with a means of pulling it out once the resin has cure. Now yu have a collapsable mandral.
That works just as well nd may be easier than getting a even coating of wax. In the second case you will need mould release while the wax serves this purpose in the first.
However it is better to use the aluminium tube as a female mould and inflate a bladder inside it. The carbon is then compressed between the bladder and aluminium providing a stronger and lighter structure than using the aluminium as a male mould.
In the female form you need an aluminium tube with at least a 3mm wall so all this has to be taken into account when calculating final beam size.