Analysis of the cause of crack in cold rolling of QSn6.5-0.1 strip

Abstract

In order to know the cause of cracks in cold rolling of QSn6.5-0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5-0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5-0.1 strip were measured by X-ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5-0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO2, S, fine-looses, the inverse segregation unable to clear up when milling, and the accumulation of all kinds of residual stresses. When the accumulation of the residual stress reaches the material’s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 °C/7 h) and milling quality (using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.