Roll bonding materials with with highly unequal material strengths - Analyses of the joining mechanism and modeling new manufacturing procedures

在对屈服强度差异很大的金属进行辊压接合期间，材料的不同流动行为会阻碍接合的形成。因此，在板坯的热轧结合中，需要长且复杂的轧制计划，而在冷轧结合期间，差异可能导致较硬层中的局部减薄和裂纹。在前两个资助期内，研究了板坯热轧粘结中的粘结形成。使用一个子程序来描述的债券形成，校准实验室，高度减少对粘结强度的影响，板厚比对轧制后的层之间的长度差的影响进行了研究。这些模拟证明，不利的几何参数和片材厚度比可能导致应力状态，这导致层之间的长度差异，即使在辊压粘合期间两层使用相同的材料。这些发现随后被用来证明找到合适的轧制参数的材料与不同的屈服强度，克服层之间的长度差异的可能性。因此，有关板坯热轧粘合的工作将在第二个资金期内顺利完成。在本提案中，将详细研究优化卷状薄带冷轧粘合的可能性。在与辊压粘结带材生产商的讨论中，薄的硬顶层与厚的软芯层的组合被认为是容易出错的，因为在这种组合中，较硬的顶层可能经历周期性的局部变薄和开裂。这些误差取决于不同的流动行为和所使用的高度降低。大的高度降低支持牢固的结合形成，但由于诱导的应力可能导致顶层失效。因此，第三个供资期的主要目标是了解所需高度降低与顶层故障发生之间的依赖关系。在此基础上，我们的目标是通过提高冷轧粘合工艺中的粘合强度来克服目前的工艺限制。因此，目前的研究结果将被转移和应用到具体的薄带。最初将进行参数研究，以了解主要影响和依赖关系。这需要调整和校准前面提到的子程序。将在模拟和实验中研究通过适当的辊缝几何形状和额外的热激活来影响层的流动行为和失效特性的选项。此外，将与LUF Paderborn合作研究通过电化学还原支持键形成的可能性。

During roll bonding of metals with greatly differing yield strength, the different flow behavior of the materials can impede the bond creation. Hence in hot roll bonding of slabs long and complex rolling schedules are required, while during cold roll bonding the differences can lead to local thinning and cracks in the harder layer. In the first two funding periods the bond formation in hot roll bonding of slabs was investigated. Using a subroutine to describe the bond formation, calibrated by laboratory experiments, the influences of height reduction on bond strength, and the influence of sheet thickness ratio on length differences between the layers after rolling were investigated. These simulations proofed that unfavorable geometric parameters and sheet thickness ratios can lead to stress states, which cause length differences between the layers even when using the same material for both layers during roll bonding. These findings were subsequently used to demonstrate the possibility to find appropriate rolling parameter for materials with different yield strength that overcome the length differences between the layers. Hence the works regarding the hot roll bonding of slabs will be finished successfully in the second funding period. In the present proposal possibilities to optimize cold roll bonding of coiled thin strips will be investigated in detail.. In discussions with producers of roll bonded strips the combination of a thin hard top-layer with a thick soft core-layer was identified to be error-prone, because in this combination the harder top-layer can experience periodical local thinning and cracking. These errors depend on the different flow behavior and the used height reduction. A great height reduction supports a firm bond formation, but can lead to failure of the top-layer due to the induced stresses. Therefore the main goal of the third funding period is to develop an understanding for the dependencies between the required height reduction and the occurrence of failure in the top-layer. Build on this understanding the aim is to overcome the present process limitations via improving the bond strength in the cold roll bonding process. Therefore the present findings will be transferred and applied to the specifics of thin strips. Initially a parametric study will be performed to achieve an understanding for the predominant effects and dependencies. This requires an adjustment and calibration of the previously mentioned subroutine. Options to influence the flow behavior and the failure characteristics of the layers via an appropriate roll gap geometry and additionally thermal activation will be investigated in simulations and experiments. Furthermore the possibility to support the bond formation via electrochemical reduction will be investigated in cooperation with the LUF Paderborn.