Abstract: The reduction of the tool rake angle in the extrusion machining process is conducive to increase the shear strain and grain refinement, but it easily leads to problems such as strip extrusion difficulties and poor surface quality. To improve the forming quality of ultrafine-grained aluminum strips and to realize the controllable strain distribution adjustment, a new process of extrusion machining with a stepped rake angle tool is proposed. By combining simulation and experiments, the strip morphology, microhardness and microstructure of 6061 aluminum alloy under different machining parameters are investigated. Extrusion machining with conventional rake angle tool is also carried out as a comparative test. The results show that the stepped rake angle tool achieves the continuous formation of ultrafine-grained strip with different strain distributions within the strip, and the ratio of high and low strain zones is adjustable by changing the thickness to be cut. This process can provide ideas and methods for tool design and ultrafine-grain material preparation.

Key words: ultrafine-grained strip, forming quality, strain distribution, stepped rake angle tool, 6061 aluminum alloy