The method comprising the following steps: a) Providing a first bath of a liquid metal (1) comprising aluminium with a content X and magnesium with a content Y, the magnesium content Y being different to zero, b) Immersing at least partially a sonotrode (3) formed from a material inert to liquid aluminium, in the first bath of liquid metal (1), and c) Applying power ultrasounds to the sonotrode (3) so as to excite the liquid metal (1) until wetting (5) of the sonotrode (3) by the liquid metal (1) is obtained. d) Cooling the first liquid metal (1) of the first bath until solidification of the first liquid metal (1) around the sonotrode (3) is obtained, generating an intimate bond (6) between the sonotrode (3) and the solidified first liquid metal (1) having a bonding strength substantially equal to that of brazing between two metals. e) Machining the solidified first metal (1) in the form of a flange (7) configured for the attachment of a mechanical amplifier and/or of a transducer (4).