Microstructural Evolutions, Hot Deformation and Work Hardening Behaviour of Novel Al–Zn Binary Alloys Processed by Squeezing and Hot Extrusion

S. Sivasankaran,K. R. Ramkumar,Hany R. Ammar,Fahad A. Al‑Mufadi,Abdulaziz S. Alaboodi,Osama Mohamed Irfan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.4

The main goals of this work were to manufacture novel Al–Zn extruded alloys by varying the Zn content (0, 10, 20, 30 wt%),investigate the microstructural evolutions, hot deformation, and work hardening behaviour by hot compression test at differenttemperatures (25 °C, 75 °C, 150 °C, 225 °C, 300 °C). Al–20Zn alloy microstructure revealed α-Al and uniform distributionof (α + η) phases, coherent (α + η) crystals in GBs with casting defect-free surfaces, and effective interactions of pinningdislocations which led to improve mechanical performance of Al–20Zn alloy, as compared to the other alloys. The observedengineering stress–strain curve results revealed the decrease of stress with increasing of temperature due to flow softening,dynamic recovery and dynamic recrystallization. These results displayed also an increase of stress value with increasingof Zn content due to the precipitation of high density (α + η) phase in the matrix and GBs, increasing of forest and mobiledislocations density with strain fields, and the formation of fine dendrites. Work hardening rate (WHR) of extruded samplesdisplayed three stages: stage I, WHR decreased slightly with increasing of temperature up to 75 °C and decreased drasticallyfrom 75 °C to 300 °C due to softening; stage II, WHR maintained constant due to balance between dislocation generationsand dislocation annihilation; stage III, WHR slightly increased due to strain hardening of (α + η) phase. WHR was observedto increase considerably with increasing of Zn content due to the formation and dispersion of high density of (α + η) phasein the Al matrix and GBs. Deformation micro-localization in terms of different characteristics was examined and reportedon the deformed samples after hot-compression test through SEM micrographs.

열간 링 압축 시험의 시편크기, 금형속도, 냉각조건이 마찰 보정선도에 미치는 영향

도영호(Y. H. DO),송민철(M. C. Song) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10

The friction is a critical factor influencing the forged shape and forging load in hot closed die forging such as hot extrusion. The purpose of this study is to establish the hot ring compression test for the effect of friction on the forged shape and forging load in hot forging process. In order to do it, the comprehensive finite element analyses were carried out to evaluate the effect of various variables such as specimen size, die speed and cooling time on the friction calibration curve of hot ring compression test. From these results, it was found that the stability of friction calibration curve could be secured through the increase of specimen size and adjustment of die speed with the specimen size.

Experimental Study and Numerical Simulation of Dynamic Recrystallization Behavior of a High-Strength Steel

X. W. Duan,J. J. Liu,B. Gong,P. Li,J. S. Liu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

In this paper, to research the dynamic recrystallization (DRX) behavior of a high-strength steel (34CrNiMo6), hot compressiontests were carried on Gleeble-1500D thermo-mechanical simulator within the different temperatures and strain rates.After hot compression tests, the microstructures of specimens were observed by optical microscope. Based on Kocks andMecking mathematics model (KM), the DRX kinetic model was established by the flow stress curves during hot deformation.Meanwhile, a grain size model was established by measuring microstructure. Furthermore, combined with the materialkinetic model and grain size model, a rigid–plastic finite element simulation was built to analyze the microstructural behaviorof 34CrNiMo6 steel during the uniaxial hot compression. The results indicate that the simulation results are in good agreementwith the experimental data. The DRX model had an accurately predictive capability for the hot compression process,which could provide a theoretical guidance and process optimization for metal forming processes.

Constitutive Analysis of 6013 Aluminum Alloy in Hot Plane Strain Compression Process Considering Deformation Heating Integrated with Heat Transfer

Gang Xiao,Qinwen Yang,Luoxing Li,Jianmin Zeng 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.1

Hot plane strain compression tests of 6013 aluminum alloy were conducted at temperatures ranging from 613 to 773 K and strain rates ranging from 10−3 to 10 s−1. A novel model is developed to describe the temperature rise considering deformation heating integrated with heat transfer in tests. The experimental flow stress data are corrected by the proposed novel model. Based on the corrected flow stress, the modified power function constitutive model is developed considering the coupled effects of deformation temperature and strain rate on flow stress. Meanwhile, another two widely used models, temperature-compensated power function and straincompensated hyperbolic sine constitutive model, are also established for the studied 6013 aluminum alloy. Finally, the three constitutive models are compared from the aspects of accuracy, stability and efficiency. It is found that the experimental flow stress is significantly affected by the temperature rise. Furthermore, the influence of heat transfer on temperature rise cannot be ignored. When the constitutive model is established, the coupled effects of deformation temperature and strain rate on flow stress should be considered. The modified power function constitutive model is the best one in describing the flow behavior among the three models.

Effect of Stress State on the High Temperature Workability of AZ31 Mg Alloy

이병호,김선미,Mohamed El Mehtedi,Enrico Evangelista,이종수 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.2

The influence of stress state on the high temperature workability of rolled AZ31 Mg alloy was investigated on the basis of a processing map. To construct the processing map, high temperature compression tests were carried out on samples oriented parallel to the rolling direction at various temperatures (25 °C~450 °C) and strain rates (10−3s−1~5s−1), and then the results were compared with those of a torsion test. The overall efficiency profiles of both the compression and torsion processing maps were similar to each other, but the index of dissipation efficiency in the torsion was somewhat lower than that in the compression. The microstructure of the compressed specimens revealed much finer grained structure than that of the torsion specimens. Such microstructural differences were attributed to the different tendencies of twin formation and texture evolution depending on the stress state.

압축시험에서의 배럴링 및 소성발열 직접 측정에 의한 Nimonic 80A 합금의 응력-변형률 선도 보정

강성훈,정희원,이호원,김세종,오영석,정재면,오세혁,김호혁 한국소성∙가공학회 2023 소성가공 : 한국소성가공학회지 Vol.32 No.4

In this study, the correction process of stress-strain curves obtained from hot compression test is introduced since the barreling induced by friction and adiabatic heat generation induced by plastic work occur under high strain rate. A shear friction factor was quantitatively estimated by measuring the dimension of barreling and temperature rise due to adiabatic heat generation was directly measured during compression test. Thereafter, the stress-strain curves were re-evaluated by introducing several equations to correct the effects of the friction and temperature rise. It was found that adiabatic factor at strain rate of 10/s is in the range of about 0.5 to 0.75 for Nimonic 80A and decreases as the assigned temperature increases.

Hot working behavior of a nitrogen-alloyed Fe-18Mn-18Cr-N austenitic stainless steel

Moon, J.,Lee, T.H.,Shin, J.H.,Lee, J.W. Elsevier Sequoia 2014 Materials science & engineering. properties, micro Vol.594 No.-

The hot workability of a nitrogen-alloyed Fe-18Mn-18Cr-N austenitic stainless steel was investigated through hot compression tests using a Gleeble simulator in a temperature range of 700-1100<SUP>o</SUP>C and at strain rates of 0.01-5s<SUP>-1</SUP>. From stress(σ)-strain(ε) curves obtained in the hot compression tests, a processing map was established to estimate the hot workability, based on the dynamic material model (DMM). The processing map predicted that the optimum hot working regimes are in the temperature range from 1050<SUP>o</SUP>C to 1100<SUP>o</SUP>C at strain rate of 0.01s<SUP>-1</SUP>. After the hot compression tests, intergranular cracking arose under most conditions, except for the optimum hot working condition predicted by the processing map. This study discusses the cause of the intergranular cracking in terms of the precipitation of intergranular Cr<SUB>2</SUB>N particles. In addition, hot ductility tests were carried out for a better understanding of the decrease in the hot workability, and a significant loss of ductility was observed with intergranular Cr<SUB>2</SUB>N precipitation.

Hot Deformation Behavior of P/M Al6061-20% SiC Composite

Asgharzadeh Hamed,Simchi Abdolreza 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicate the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The mechanism of deformation was found to be controlled primarily by dynamic recrystallization.

1Cr-1.25Mo-0.25V 합금강의 단조 전 균질화 처리에 따른 미세조직 변화 및 고온변형 안정성 평가

권거영 ( Keo Young Kwon ),나영상 ( Young Sang Na ),서성문 ( Seong Moon Seo ),양재규 ( Jea Kyu Yang ),김양도 ( Yang Do Kim ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.12

In order to investigate the effects of homogenization treatment on microstructural change and high temperature deformation stability, a series of hot compression tests and homogenization treatment were conducted for as-cast and upset-forged 1Cr-1.25Mo-0.25V steels. Microstructural inhomogeneity like dendritic morphology and elemental segregation in as-cast steel was homogenized after 10 hours-holding at 1200 ℃, followed by the rapid grain coarsening up to about 700 μm after 20 hours-holding. However, upset- forged steel showed rapid grain coarsening even in the early stage of high temperature holding at 1200 ℃. Compression tests for the 1Cr-1.25Mo-0.25V steels showed that flow stresses of as-cast 1Cr-1.25Mo-0.25V steel were higher than those of the upset-forged at temperatures lower than 1000 ℃. By analyzing the compression test results based on a dynamic materials model, we concluded that the microstructural inhomogeneity diminished hot deformation stability of the as-cast 1Cr-1.25Mo-0.25V steel. It is clear that the microstructural homogenization of as-solidified steel prior to upset forging is essential for improving the hot deformation stability and soundness of hot forgings.

동적 페라이트 변태에 미치는 오스테나이트 과냉도의 영향

洪承讚,林成煥,李景鍾,李經燮 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.1

Hot compression test was performed to examine the effect of degree of undercooling on dynamic ferrite transformation behavior. Austenite undercooling was controlled by cooling rate from austenitization temperature to deformation temperature. The degree of undercooling was determined as ΔT (=Ae_3 - Ar_3). Ae_3 temperature was calculated by using Thermo-Calc and Ar_3 temperature was measured by dilatometry. The fine grained ferrite was formed during 70% deformation just above Ar_3 temperature. It was observed that the average ferrite grain size was 2 ㎛ regardless of temperature. At this temperature the flow stress was decreased by ferrite formation during deformation. The amount of ferrite transformed dynamically was increased as ΔT was increased. While, the ferrite grain size was mainly influenced by the amount of deformation. It was also confirmed that the critical strain of dynamic ferrite at high cooling rate to deformation temperature was shifted to lower strain compared to that at low cooling rate with the aid of increasing undercooling.