Hydrostatic cyclic expansion extrusion (HCEE) as a novel severe plastic deformation process for producing long nanostructured metals

Abstract

In this paper, hydrostatic cyclic expansion extrusion (HCEE) is developed as a new severe plastic deformation technique for processing of the relatively longer ultrafine grained samples. Increasing the length of the processed sample, decreasing the processing load astonishingly, and increasing the hydrostatic stresses are the main advantages of HCEE. In This process lubricant surrounded around workplaces plays the main role in reducing the friction load and increase pressure hydrostatic. HCEE process was executed to commercial pure aluminum 1050 at room temperature, and microstructural evolution and the mechanical properties were examined. Microstructure evolution of this process was investigated by transmission electron microscopy (TEM) and back-scattered diffraction (EBSD). TEM and EBSD revealed an ultrafine grained microstructure after the two passes of the HCEE process. The average size of grains and subgrain decreased from 50µm in the annealed sample to 0.76µm after two passes of the process. Mechanical properties such strength and hardness improved because of the large effect strain. Yield and ultimate strength were increased from 40 MPa and 52 MPa to 109 MPa and 115 MPa just after one pass of HCEE process, also Microhardness was increased from 36 HV to 45 HV at first passes.

An Overview on the Continuous Severe Plastic Deformation Methods

“…It was shown that it can even process hard to deform materials. 78) Very recently, Samadpour et al 79) introduced an efficient technique in which the fluid pressure is used to remove frictional force and the material is deformed by hydraulic pressure. 80) This technique can be a promising step to design a frictionless process making possible the producing UFG large samples while applying relatively higher hydrostatic stresses.…”

“…A prominent example is related to HCEE process in which the friction force and deformation load are reduced to increase the sample size (l/d) from ³5 in regular CEE to more than 10 mm in HCEE. 80,140) In some of the semicontinuous processes in which drawing is applied at the outlet like ECAD, the tensile stress at the outlet side should not exceed from the yield strength of the material otherwise the plastic deformation is limited by yielding the sample. For example, the angle between input and output channels in ECAD process should be larger to prevent different damages in final products.…”

“…As is evident, although the effective strain in Conshearing and HCEE samples are approximately equal, the final grain size attained in conshearing is twice of that one in HCEE. 150,151) The reason for this case is concerned with the difference in hydrostatic pressure in these two processes. In general, the hydrostatic pressure in processes based on pressing is more than that of another process; therefore, this can help to attain the smaller grain size in the final products.…”

“…First cycle of the HCEE process (a) first stage, (b) expansion stage 79). Scheme of continuous ECAD process 29).…”

ECAP-treated aluminium alloy AA2030: microstructure and mechanical properties

“…[1][2][3] The SPD processes provide for an accumulation of high-degree deformation, which contributes to the formation of high-angle grain boundaries. [4][5][6] UFG materials are characterized by an increased complexity of mechanical, physical and operational characteristics. [7][8][9][10] The main ones include properties such as tensile strength, yield strength under tension or compression, hardness, microhardness, corrosion resistance, and others.…”