Deformation and strain analysis for grain refinement of materials processed through equal channel angular pressing

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Abstract

Among the various metal forming forms ECAP is one method in which nano crystalline and ultrafine grain metal and amalgams are formed. This method is used for high strain super plasticity in the material by grain refinement to the nano or submicron level, without changing the dimensions of work piece. In this process metal is forced to pass repeatedly through the specially designed channel die with intersectional channel for different angels. The modeling of the die and the billet was done through SOLIDWORKs 2017 and quantitative analysis was done through ANSYS workbench 15.0 software. The result was compared with practical results for different channel angle and it was observed that the ideal parameters for most extreme homogeneity in strain can be accomplished with channel angle Φ = 900, corner angle Ψ = 150 and coefficient of friction μ = 0.25.

Introduction

Among different severe plastic deformation (SPD) techniques, multiaxial forging, accumulative roll bonding, high pressure torsion straining, equal channel angular pressing (ECAP) etc. The last procedure is the most encouraging and interesting because of its capacity of delivering enormous examples with the ultrafine grain estimate by rehashing the procedure while keeping up the original cross-section of the work piece. The real distinction of ECAP with other forms is that twisting happens in prompt regions i.e. at the intersection of the two channels. In this way, the changes in ECAP prepared samples are exceptionally limited and homogeneous in the confined deformation zone. This procedure, stated by Segal et al. [1] in the start of 1980′s has been the topic of study these years. Subsequently, improved mechanical, high strain and physical properties, outrageous fine size grains and fluctuating surfaces could be acquired in the materials to be processed. In this paper, the impacts of strain hardening attributes of the material, exponent (n) of Holloman’s law [3] and strain hardening coefficient (K), on strain homogeneity and corner gap development in ECAP procedure were researched quantitatively by finite element method (FEM). On general notations in ECAP, various angles in geometries are described as channel angle Φ, corner angle Ψ; in order to observe the effect of corner angle in this study.

Effective theoretical strain (ε) according to geometry is given by Iwahashi et al. [4]. is given in Eq. (1)=n32cotΦ+Ψ2+ΨcosecΦ+Ψ2

Fig. 1 shows the ECAP principle where there is a die having a bent internal channel angle and corner angle which shows outer arc of curvature and the two intersecting channels. Billet is machined or load is applied to pass the channel in a die. In the die billet is pressed using plunger through the channel of the die respectively (the detailed study about these angles have been discussed above). In this test an attempt has been made to find the best possible parameters where we can get max result in strain homogeneity. As the cross sectional area is unchanged, the sample through die is passed repetitively to attain the exceptionally high strain. So this test is performed for Φ from 900 to1200, Ψ equal to 00 with an increment of 150 for both angles to get the maximum possible results. The sample is passed again and again through the path in the die to get better refinement. [4], [5], [6], [7]

The previous investigations expected two-dimensional (2D) guess of plane strain condition and didn’t discussed much about the stress and strain inhomogeneity. Results got by 2D analysis give restricted data, which includes lots of mistakes and not accurate results. In this paper, the impacts of die parameters is analyzed using simulation software ansys workbench on shear strain delivered in the Aluminum alloy material, which at last causes the grain refinement.

Section snippets

Simulation procedure

FEM analyses of ECAP procedure were analyzed using commercial FEM code Ansys workbench 15.0. The model was developed by considering plane strain condition and a plane going through the center point of the billet and die. The ram and the die are displayed as analytical inflexible bodies [5], [6], [7] According to theoretical and experimental results; isothermal condition is satisfied at low pressing speed. The Aluminum alloy AA1080 was utilized as the billet material in software stimulations.

Results and discussion

In this paper the main focus is on the effects of these parameters–Φ,Ψ, µ, ɛ, punch load. We are going to evaluate or compare all of these parameters with each other with the help of analytical observations and graphs and will compare the analytical results. The result of different phases are compared with different channel angles 900, 1050, 1200, corner angle equal to 00, results will be taken for two frictional cases i.e. for µ = 0 and µ = 0.25.

Three phases of the load by ECAP can be

Conclusion

FEM simulations were done on ansys workbench 15.0 with explicit dynamics to study the effect of strain and deformation in the material when passed through die with different channel angles under both friction and frictionless case. The punch load is applied on the workpeice of material Aluminum alloy 1080 with the help of ram and the workpeice is allowed to pass through the die of material Tool steel H13, which has much more strength than Aluminum 1080AA. There are combination cases of study as

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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