brass is a mixture of zinc and copper so even if you could deposit it by electroplating, I suspect you could have trouble with electro-chemical stability with aluminium as a base.
You could zincate the alu surface first, then the brass will adhere...
Anodic: Al + 3 OHn n> Al(OH)3 + 3en
Al(OH)3 n> AlO2n + H2O + H+
Cathodic: H+ + en n> H n> 1/2H2 (g)
...
Cathodic: Zn(OH)42n n> Zn2+ + 4 OHn
Zn2+ + 2en n> Zn (s)
When plating with brass, IE copper, one should also use zinc sulfate rather than zinc oxide.. for a better result.
But as Steve Eddy says, it is a little tedious, and hence expensive... to brassify aluminum.
Imperial