Improved method of fabricating boron fiber and aluminum matrix composite structures, especially gas turbine compressor blades having titanium metal skins. Titanium skins (32, 32') and boron aluminum composite cores (34) are preformed by gas pressure and hard dies prior to hot pressing. The composite sheets (34) of the core are preformed with the use of expendable carrier sheets (36, 38) which hold the stacked sheets firmly as both the carrier sheets and composites are shaped through moderate temperature and gas pressure against a hard die (46). The preforming permanently shapes and lightly bonds the composite sheets. The skins (32, 32') are preformed in an analogous process using gas pressurization of a metal envelope into die cavities (24, 24'). The skins and composite core are then hot pressed in hard dies (54, 54') to form the finished part.