Problems of ultrafine grained structures in some aluminum alloy workpieces and their solutions by severe plastic deformation methods

Abstract

Numerous studies have found that one of the most progressive areas of improving the quality of sheet metal is to obtain a more fine-grained structure. The aim of the research is to design the rational technology of rolling strips from aluminium alloys with ultra-fine grained structure by uniform distribution of stress-strain state and refinement of the microstructure of the metal. The quantitative data has been obtained and the basic stress-strain state, as well as temperature distribution patterns was established by the MSC.SuperForge program during modelling rolling in the helical rolls and longitudinal wedge mill with different numbers of passages and the single reduction. It is proved that rolling in the helical rolls with oppositely located projections and depressions leads to the localization of SSS in the contact zones of the work piece at the beginning of the rolling, and then in the zones under the inclined portions of the projections and depressions of the rolls. It is established that deforming in the stands of the LWM allows gradually to transform accent of the SSS from the surface zones to the central layers of the work piece, and after that uniformly deform the strips along the length of it. The rational technology of aluminium alloys rolling was developed and tested in the laboratory. The special attention is paid to analysis of the influence of the rolling conditions in the helical rolls and LWM on the formation of the microstructure of aluminium alloy. Research results of the microstructure evolution of long length work pieces at the different stages of their production show the possibility to manufacture the strips with UFG structure by using helical rolls and LWM.