of welding thereby providing at least partially closed side rails 16 18 as best illustrated in detail in fig2 d in one particularly useful embodiment of the motor vehicle sub frame 10 the walls 40 46 of the components 20 32 are welded together by one or more friction stir welds as best illustrated in fig1 the first extrusion axis 22 of the first component 20 runs laterally while the second extrusion axis 34 of the second component 32 runs vertically in the assembled sub frame 10 the two extrusion axes 22 34 may form an included angle of between 60 u00b0 and 90 u00b0 or of between 70 u00b0 and 90 u00b0 or of between 80 u00b0 and 90 u00b0 in the illustrated embodiment the two extrusion axes 22 34 are substantially perpendicular to one another reference is now made to fig3 and 4 illustrating in detail the rear cross member 14 of the sub frame 10 as illustrated the rear cross member 14 includes an extruded hollow body 48 having an extrusion axis 50 that extends laterally across the sub frame 10 a series of walls 52 are positioned inside the hollow body 48 and extend across the hollow body each wall 52 includes a first edge 54 and a second opposite edge 56 that are joined to the inner surface of the hollow body 48 by appropriate welds in the illustrated embodiment each wall 52 has a longitudinal axis that extends parallel to the extrusion axis 50 of the hollow body 48 further each wall 52 is planar as further illustrated in fig3 and 4 the hollow body 48 includes various attachment holes 58.