Integral thin shells made of high strength aluminum alloys are urgently needed in new generation transportation equipment. There are challenges to overcoming the co-existing problems of wrinkling and splitting by the cold forming and hot forming processes. An innovative technology of ultra-low temperature forming has been invented for aluminum alloy thin shells by the new phenomenon of 'dual enhancement effect'. That means plasticity and hardening are enhanced simultaneously at ultra-low temperatures. In this perspective, the dual enhancement effect is described, and the development, current state and prospects of this new forming method are introduced. This innovative method can provide a new approach for integral aluminum alloy components with large size, ultra-thin thickness, and high strength. An integral tank dome of rocket with 2 m in diameter was formed by using a blank sheet with the same thickness as the final component, breaking through the limit value of thickness-diameter ratio.

In order to meet the requirements of high reliability, long-lifetime and lightweight in a new generation of aerospace, aviation, high-speed train, and energy power equipment, integrated components are urgently needed to replace traditional multi-piece, welded components. The applications of integrated components involve in a series of large-size, complex-shaped, high-performance components made of difficult-to-deform materials, which present a huge challenge for forming ultra-large size integrated components. In this paper, the developments and perspectives of several extreme forming technologies are reviewed, including the sheet hydroforming of ultra-large curved components, dieless hydroforming of ellipsoidal shells, radial-axial ring rolling of rings, in situ manufacturing process of flanges, and local isothermal forging of titanium alloy components. The principle and processes for controlling deformation are briefly illustrated. The forming of typical ultra-large size integrated components and industrial applications are introduced, such as the high strength aluminum alloy, 3 m in diameter, integrated tank dome first formed by using a sheet blank with a thickness the same as the final component, and a 16 m diameter, integrated steel ring rolled by using a single billet. The trends for extreme forming of ultra-large size integrated components are discussed with a goal of providing ideas and fundamental guidance for the further development of new forming processes for extreme-size integrated components in the future.