Abstract
A multi-pass equal-channel angular pressing (helical channel angular pressing-parallel channel, HCAP-PC) is proposed to enhance process efficiency and avoid plastic deformation damage during the preparation of ultrafine-grained age hardened aluminum alloys. Multiple shear and twist deformations are provided at the single extrusion channel. The channel parameters were optimized by using grey relational analysis (GRA). An orthogonal L16-4-5 test array containing five factors (ψ, ϕ, γ, m and the length of L1 section) and four levels was collected to investigate the influence of channel parameters on the effective strain, the effective stress, the amount of damage and the deformation homogeneity coefficients. Based on the GRA, the grey relational coefficients and the grey relational grades were calculated to report the significant channel parameters which affect the extrusion quality and efficiency. Furthermore, according to the results of segregated grey relational grades, the contribution orders from high to low were listed as ψ, ϕ, γ, m and L1. The extrusion experiments were carried out with aluminum alloy 2024 after solid solution treatment and at the HCAP-PC die with geometry of ψ 20°, ϕ 90°, γ 73°, m 1.35 and 1d. The ultrafine-grained age hardened aluminum alloys were prepared and the process time was decreased to less than 120 min.
Highlights
The equal-channel angular pressing (ECAP) process is regarded as an efficient and feasible method to prepare bulk ultrafine-grained materials which exist with average grain sizes of less than 1 μm
A minimum of 4 extrusion passes were required to obtain the ultrafine-grained microstructure at ECAP [2]
Mechanical treatments are needed to make the extruded specimen fit the geometry of the ECAP channel after each pass
Summary
The equal-channel angular pressing (ECAP) process is regarded as an efficient and feasible method to prepare bulk ultrafine-grained materials which exist with average grain sizes of less than 1 μm.The microstructure is quite homogeneous and consists of an array of essentially equiaxed grains with many boundaries having high angles of misorientation [1]. A minimum of 4 extrusion passes were required to obtain the ultrafine-grained microstructure at ECAP [2]. Experiments on face-centered cubic (fcc) aluminum alloys have shown that route BC is the optimal processing route for having better microstructure and mechanical properties [3,4]. It is difficult for the extruded specimen to be pushed into the ECAP channel again once the billet has been extruded out from the channel because the original size cannot always be maintained.
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