Superplastic deformation of diffusion bonded aluminium structures

Claim 1

A method of superplastically forming a sandwich structure from a plurality of aluminum alloy sheets, the method comprising: assembling a stack of aluminum alloy sheets in face-to-face relationship, said stack comprising a pair of outer sheets and at least one core sheet; providing reinforcing material in the stack in the zones where diffusion bonding is to be carried out, diffusion bonding the sheets in bonding zones according to a predetermined pattern to create a workpiece having internal cavities; heating the workpiece to the superplastic forming temperature of the alloy sheets, and applying gas pressure to the cavities to the effect superplastic deformation of the workpiece, said reinforcing material thereby serving to prevent tensile stresses exerted during subsequent superplastic forming from causing peel fracture of the diffusion bonds such that superplastic strain occurs selectively in those regions of the workpiece between the diffusion bonded zones.

Claim 2

A method of superplastically forming a sandwich structure from a plurality of aluminum alloy sheets, the method comprising: assembling a stack of aluminum alloy sheets in face-to-face relationship, said stack comprising a pair of outer sheets and at least one core sheet; providing reinforcing material in the stack in the zones where diffusion bonding is to be carried out, diffusion bonding the sheets in bonding zones according to a predetermined pattern to create a workpiece having internal cavities; heating the workpiece to the superplastic forming temperature of the alloy sheets, and applying gas pressure to the cavities to the effect superplastic deformation of the workpiece, said reinforcing material thereby serving to prevent tensile stresses exerted during subsequent superplastic forming from causing peel fracture of the diffusion bonds such that superplastic strain occurs selectively in those regions of the workpiece between the diffusion bonded zones.

Claim 6

A method of superplastically forming a sandwich structure from a plurality of aluminum alloy sheets, the method comprising:. assembling a stack of aluminum alloy sheets in face-to-face relationship, said stack comprising a pair of outer sheets and at least one core sheet; diffusion bonding the sheets in bonding zones according to a predetermined pattern to create a workpiece having internal cavities; heating the workpiece to the superplastic forming temperature of the alloy sheets, and applying gas pressure to the cavities to the effect superplastic deformation of the workpiece, characterised in that reinforcing material is provided in the stack prior to the diffusion bonding step in the zones where diffusion bonding is to be carried out, said reinforcing material thereby serving to prevent tensile stresses exerted during subsequent superplastic forming from causing peel fracture of the diffusion bonds such that superplastic strain occurs selectively in those regions of the workpiece between the diffusion bonded zones, further characterised in that the reinforcing material comprises separate pieces such as strips or patches bonded to the parent sheet material in a predetermined pattern, and further characterised in that the reinforcing material has a relatively higher stiffness than the parent sheet material at the superplastic forming temperature of the latter.

Claim 7

A method of superplastically forming a sandwich structure from a plurality of aluminum alloy sheets, the method comprising:. assembling a stack of aluminum alloy sheets in face-to-face relationship, said stack comprising a pair of outer sheets and at least one core sheet; diffusion bonding the sheets in bonding zones according to a predetermined pattern to create a workpiece having internal cavities; heating the workpiece to the superplastic forming temperature of the alloy sheets, and applying gas pressure to the cavities to the effect superplastic deformation of the workpiece, characterised in that reinforcing material is provided in the stack prior to the diffusion bonding step in the zones where diffusion bonding is to be carried out, said reinforcing material thereby serving to prevent tensile stresses exerted during subsequent superplastic forming from causing peel fracture of the diffusion bonds such that superplastic strain occurs selectively in those regions of the workpiece between the diffusion bonded zones, further characterised in that the reinforcing material comprises separate pieces such as strips or patches bonded to the parent sheet material in a predetermined pattern, and further characterised in that the reinforcing material has a relatively higher stiffness than the parent sheet material at the superplastic forming temperature of the latter.

Claim 9

A method of superplastically forming a sandwich structure from a plurality of aluminum alloy sheets, the method comprising: assembling a stack of aluminum alloy sheets in face-to-face relationship, said stack comprising a pair of outer sheets and at least one core sheet; diffusion bonding the sheets in bonding zones according to a predetermined pattern to create a workpiece having internal cavities; heating the workpiece to the superplastic forming temperature of the alloy sheets, and applying gas pressure to the cavities to the effect superplastic deformation of the workpiece, characterised in that reinforcing material is provided in the stack prior to the diffusion bonding step in the zones where diffusion bonding is to be carried out, said reinforcing material thereby serving to prevent tensile stresses exerted during subsequent superplastic forming from causing peel fracture of the diffusion bonds such that superplastic strain occurs selectively in those regions of the workpiece between the diffusion bonded zones, further characterised in that the reinforcing material comprises separate pieces such as strips or patches bonded to the parent sheet material in a predetermined pattern, wherein the parent sheet material is formed of an aluminum-lithium alloy and the reinforcing material is formed of a metal matrix composite comprising a particulate reinforcement of silicon carbide in a matrix of aluminum-lithium alloy.

Claim 10

A method of superplastically forming a sandwich structure from a plurality of aluminum alloy sheets, the method comprising: assembling a stack of aluminum alloy sheets in face-to-face relationship, said stack comprising a pair of outer sheets and at least one core sheet; diffusion bonding the sheets in bonding zones according to a predetermined pattern to create a workpiece having internal cavities; heating the workpiece to the superplastic forming temperature of the alloy sheets, and applying gas pressure to the cavities to the effect superplastic deformation of the workpiece, characterised in that reinforcing material is provided in the stack prior to the diffusion bonding step in the zones where diffusion bonding is to be carried out, said reinforcing material thereby serving to prevent tensile stresses exerted during subsequent superplastic forming from causing peel fracture of the diffusion bonds such that superplastic strain occurs selectively in those regions of the workpiece between the diffusion bonded zones, further characterised in that the reinforcing material comprises separate pieces such as strips or patches bonded to the parent sheet material in a predetermined pattern, wherein the parent sheet material is formed of an aluminum-lithium alloy and the reinforcing material is formed of a metal matrix composite comprising a particulate reinforcement of silicon carbide in a matrix of aluminum-lithium alloy.