the low peel strengths of diffusion bonded joints in aluminum alloy structures has been a bar to their use in superplastic forming . the invention overcomes this disadvantage by creating a workpiece intended for subsequent superplastic forming by diffusion bonded assembly of alloy sheets in bonding zones according to a predetermined pattern and providing reinforcing material in the workpiece in the region of the diffusion bonded zones . the reinforcing material serves to prevent the tensile stresses exerted during subsequent superplastic forming from initiating peel fracture of the diffusion bonds . instead , the tensile stresses act so as to bring about superplastic deformation in those regions of the workpiece between the diffusion bonded zones .