A composite rotor assembly adapted for use in an electromagnetic friction coupling comprising two armatures concentric with each other and a single fixed electromagnet with coaxial winding able to be excited with a reduced excitation for recalling only the innermost armature and with a full excitation for recalling both of the armatures, the composite rotor assembly comprising: an annular body made of ferromagnetic material and suitable for transporting a magnetic flux, the annular body comprising: a front surface integral with a coaxial sleeve, the coaxial sleeve extending towards a rear side in a longitudinal-axial direction (X-X) and suitable for coupling with a support shaft; wherein a radially outer edge of the annular body extends axially towards the rear side; wherein an inner gap is formed in the annular body and continuously extends along a circumference of the annular body, along a diameter greater than the diameter of the coaxial sleeve and coaxial therewith; wherein a continuous outer gap is arranged along a circumference of the annular body, is concentric with said inner gap, and has a diameter comprised between the outer diameter of the front surface and the diameter of said inner gap; wherein a continuous intermediate gap is arranged along a circumference of the annular body, is concentric with said inner recess, and has a diameter comprised between the diameter of the outer gap and the diameter of said inner gap; characterised in that said inner, outer and intermediate gaps (135, 636, 637) are filled with a solid non-magnetic welded material and suitable for interrupting the continuity of a magnetic flux; wherein the annular body is formed with concentric outer, intermediate and inner annular sectors of ferromagnetic material, with the outer annular sector radially comprised between the radially outer edge of the annular body and the outer gap, the inner annular sector radially comprised between the inner gap and the intermediate gap, and the intermediate annular sector radially comprised between the intermediate gap and the outer gap; wherein the annular body has either: a plurality of radial holes, which are angularly spaced from each other, and which receive radially extending pins made of ferromagnetic material and extending radially from the outer annular sector to the inner annular sector; or a ferromagnetic annular plate (739;839) fixed to a rear surface of the annular body and radially extending between the radially outer edge of the annular body and the inner annular sector; the pins or plate (739;839) allowing radial passage of a magnetic flux between the outer annular sector and the inner annular sector of the annular body. a front surface integral with a coaxial sleeve, the coaxial sleeve extending towards a rear side in a longitudinal-axial direction (X-X) and suitable for coupling with a support shaft; wherein a radially outer edge of the annular body extends axially towards the rear side; wherein an inner gap is formed in the annular body and continuously extends along a circumference of the annular body, along a diameter greater than the diameter of the coaxial sleeve and coaxial therewith; wherein a continuous outer gap is arranged along a circumference of the annular body, is concentric with said inner gap, and has a diameter comprised between the outer diameter of the front surface and the diameter of said inner gap; wherein a continuous intermediate gap is arranged along a circumference of the annular body, is concentric with said inner recess, and has a diameter comprised between the diameter of the outer gap and the diameter of said inner gap; characterised in that said inner, outer and intermediate gaps (135, 636, 637) are filled with a solid non-magnetic welded material and suitable for interrupting the continuity of a magnetic flux; wherein the annular body is formed with concentric outer, intermediate and inner annular sectors of ferromagnetic material, with the outer annular sector radially comprised between the radially outer edge of the annular body and the outer gap, the inner annular sector radially comprised between the inner gap and the intermediate gap, and the intermediate annular sector radially comprised between the intermediate gap and the outer gap; a plurality of radial holes, which are angularly spaced from each other, and which receive radially extending pins made of ferromagnetic material and extending radially from the outer annular sector to the inner annular sector; or a ferromagnetic annular plate (739;839) fixed to a rear surface of the annular body and radially extending between the radially outer edge of the annular body and the inner annular sector; the pins or plate (739;839) allowing radial passage of a magnetic flux between the outer annular sector and the inner annular sector of the annular body.