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Friction Stir Radial Backward Extrusion (FSRBE) as a new grain refining technique

Jafarzadeh H., Babaei A., Esmaeili-Goldarag F.

Archives of Civil and Mechanical Engineering

2018

Vol. 18, no. 4

1374--1385

A new method entitled Friction Stir Radial Backward Extrusion (FSRBE) is presented for processing fine-grained tubes. In FSRBE technique, an initial pure copper billet is placed inside a cylindrical chamber. The billet is pushed toward a rotating tool which results in radial and backward flow of the material while is frictionally stirred. The microstructure evolution during FSRBE was investigated through experimental observations and cellular automaton (CA) modeling. The observations reveal that the microstructure with initial grain size of 75 μm was refined to a fine-grained structure with an average grain size of 12 μm. The results of tensile tests demonstrate slight improvement in the value of yield and ultimate strength, elongation and microhardness. The microstructural evolution during FSRBE processing in the micro-level was studied using a coupled cellular automaton algorithm and finite element model. First, the macroscopic plastic flow behavior of material during FSRBE was calculated using FEM simulation method. Next, by tracing the plastic strain, the strain rate and temperature, in the deformation domain of cellular automaton, the DRX kinetics of pure copper is obtained in a devised post-processing step. The microstructure observations showed that the proposed model predictions were in reasonably good agreement with the experimentally obtained results.

Refinement of steel microstructure by free-forging

Jandová D., Divišová R., Skálová L., Drnek J.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 16, nr 1-2

17--24

Purpose: Refinement of austenitic steel and low alloyed C-Mn-Si-Nb steel microstructure by free-forging. Design/methodology/approach: In this study severe hot deformation was applied on low alloyed 0.2C-1.5Mn-2Si-0.05Nb steel and austenitic 0.07C-18Cr-2Mn.-10Ni steel. Steels were processed in a full-hydraulic press. Different temperatures of preheating, dwells and strain levels were applied. Microstructure was characterised using optical metallography, scanning and transmission electron microscopy. Findings: After optimization of processing fine grained structures with convenient phase composition were obtained. Multiple free-forging followed by recrystallization annealing was successfully used for refinement of austenitic Cr-Ni steel and improvement of mechanical properties. While free-forging of low alloyed C-Mn-Si-Nb steel still has not satisfied expected increase of strength and ductility. Research limitations/implications: Free-forging usually results in formation of very heterogeneous structures. In submitted study relatively fine grained and uniform structures were obtained. Grain size below a few micrometers can not be probably achieved using above mentioned technology. Originality/value: Obtained results can be used for development of forging technology in service conditions.

Crystallization of Al-Si alloys in the course of high pressure die-casting

Nova I., Exner J., Hošek Z., Novakova I.

Archiwum Odlewnictwa

2004

R. 4, nr 14

325-332

The article deals with the study of crystallization processes of die-casting applied especially for the AISi9Cu3 alloy. The crystallization of the studied casting was performed by using of the microscope VEGA TS 5130. The structure was observed for thin (3mm) and in thick (11 mm) casting. There is a crystalline fine-grained structure of the die-casting. There is not a dendritic structure in the die-casting.

Artykuł dotyczy badań procesów krystalizacji odlewów ciśnieniowych w szczególności stopu AISi9Cu3. Badania procesu krystalizacji testowanego odlewu zrealizowano na mikroskopie VEGA TS 5130. Analizowano strukturę odlewu w ściankach o grubości 3 mm, 11 mm. Zaobserwowano w odlewie ciśnieniowym drobnoziarnistą strukturę krystaliczną. Struktura dendrytyczna nie występowała w badanym odlewie.