Softening Effect on Fracture Stress of Pure Copper Processed by Asynchronous Foil Rolling

In order to study the size effect on the mechanical property of micro-scale metal, pure copper strips with thicknesses in the range of 20 µm to 600 µm were obtained through the asynchronous foil rolling technology. Progressive mechanical property tests indicated that the pure copper experiences softening effect at a micro-scale when the thickness is below 80 µm, which is contrary to the traditional work hardening theory. The related mechanisms were analyzed and discussed through the observation of microstructure and fracture morphology. The decrease of fracture stress with the decrease of thickness can be attributed to the decreased interfacial energy and dislocation density, which contributes to the release of the cumulative distortion energy and the tendency to soften. In addition, the distribution of misorientation angle and changed Taylor factor with the decrease of thickness are other important factors. The fracture morphology indicated a reduction in the number of micro-voids and the nature of fracture transformed from dimpled pattern to knife edge rupture with thickness. The traditional Hall-Petch relationship is no longer applicable due to the softening effect. A modified Hall-Petch relation considering the distribution of misorientation angle and Taylor factor was established, which provided a better relationship between flow stress and grain size.

Strengthening Effects of Single Particle with Different Mechanical Property on Ultra-Thin Rolling of AA1235 Aluminum Alloys

In aluminum foil rolling, the secondary particles may lead to stress concentration at the boundary between these particles and the matrix. Different types of particles would result in stress concentration at different levels. The three dimensional finite element modeling (3D-FEM) was used to simulate the effect of the particles with different hardness on mechanical properties of the matrix of AA1235 aluminum foils in its foil rolling process. The hardness ratio was used to evaluate the mechanical property of foils. It has been found that when the hardness ratio of the particle was similar to that of the matrix (R=1), the interaction mechanism of the dislocations with the particle was dislocation cutting way. When the hardness ratio of the particle to the matrix increased from 1 to 6, the interaction mechanism of the particle with the matrix changed from the dislocation cutting way to the Orowan dislocation bypass way. When the hardness ratio increased to as high as 6, dislocation interacted with the particle only by the Orowan dislocation bypass way.

A Review of Cooling Technologies for Flat Rolled Aluminium Products

The basic principles of the cold and foil aluminium rolling technology used in most rolling plants today have been around for many years with the major flatness control developments taking place 30 years ago. A crucial component of this technology is the coolant and lubricant fluid used for this process. In cold and foil rolling, kerosene is used as a coolant for the work rolls and as a lubricant for the rolling process, with the aid of specific additives. A lot of alternatives have been tested in the past but the kerosene medium has remained as the industry standard. An overview of the alternative technologies is discussed.