This study investigates the forming limits of cryo-rolled Ultrafine Grained (UFG) aluminium sheet for loading conditions relevant to sheet metal forming.

It is shown that a combination of nano-particle strengthening with an annealing heat treatment enables the production of cryo-rolled UFG aluminium with up to 12 % higher material strength and 20 % higher formability compared with the unreinforced UFG condition. While nano-particle strengthening does not significantly influence the tensile ductility, it reduces the bend fracture limit by over 50 % due to an increased dislocation density and a diffuse sub-grain structure. The level of the forming limit curves (FLD) of all UFG materials was up to 5 times higher than their uniform tensile elongation and hardening index; this is attributed to a high strain-rate sensitivity, which increased with annealing heat treatment.

In roll forming, the UFG aluminium showed similar material behaviour and shape defects as observed for conventional sheet metals in previous studies. However, given the reduced bend fracture limits observed with nano-particle addition, this study suggests that roll forming may not be a suitable manufacturing solution for nano-particle strengthened UFG sheet metal.

这项研究调查了冷轧超细晶粒（UFG）铝板在与钣金成形相关的载荷条件下的成形极限。

结果表明，纳米颗粒强化与退火热处理相结合，可以生产比未经强化的UFG条件高12％的材料强度和20％的可成形性的冷轧UFG铝。尽管纳米颗粒的强化不会显着影响拉伸延展性，但由于位错密度的增加和亚晶粒的弥散结构，使弯曲断裂极限降低了50％以上。所有UFG材料的成形极限曲线（FLD）的水平比其均匀的拉伸伸长率和硬化指数高出5倍；这归因于高应变速率敏感性，其随着退火热处理而增加。

在轧制成形中，UFG铝表现出与先前研究中常规钣金相似的材料性能和形状缺陷。但是，鉴于添加纳米颗粒后观察到的弯曲断裂极限降低，这项研究表明，辊压成型可能不是纳米颗粒强化UFG钣金的合适制造解决方案。