To provide a hollow extruded material of an aluminum alloy for a weld structure, which shows superior formability in particular in a part of a cross section and superior weldability in particular in the other part of the cross section.

A bumper reinforcing member 35 is formed of the extruded material of the aluminum alloy; and the cross section is constituted by a part formed of a 6000 series aluminum alloy (top and bottom webs 39 and 40) and a part formed of a 7000 series aluminum alloy (front and back flanges 36 and 37, and middle web 38). A front-end of a transversely crushing type stay 42 formed of the extruded material of the 7000 series aluminum alloy is welded (welded part 44) to the back flange 37 of the bumper reinforcing member 35. The bumper reinforcing member 35 and the stay 42 are aged on an aging treatment condition of the 6000 series aluminum alloy before or after the welding step.