I've only scanned this so far, but it seems to prove that BA does react with Al and form a surface layer.
Surface mechanism of the boron adsorption on alumina in aqueous solutions
The adsorption of boron (boric acid) from aqueous solutions on alumina has been
investigated at pH 8.0, I = 0.1 M NaClO 4, T = 22 ± 3˚C, and under normal atmospheric condi-
tions. The characterization of the adsorbed species was performed by Raman spectroscopy
and the spectroscopic speciation was assisted by theoretical DFT calculations. Evaluation of
the spectroscopic data points to the formation of inner-sphere surface complexes and indi-
cates the formation of two different types of adsorbed boron species. The theoretical calcula-
tions corroborate the spectroscopic data and indicate that at low boron concentration the
monodentate surface species dominates, whereas increased boron concentration favors the
formation of a bidentate surface species...
https://sci-hub.ru/10.1080/19443994.2013.764354