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1

A technique to achieve an excellent strength-ductility balance in AA2024 alloy

Roodgari Mohammad Reza, Jamaati Roohollah

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e12, 2023

EN

In the current study, the microstructure and mechanical properties of AA2024 alloy produced by a new technique consisting of solution treatment, instantly followed by asymmetric cold rolling with a reduction of 65%, and subsequent artificial aging (heat treatment) with four temperatures of 190, 300, 400, and 500 °C was investigated. The additional shear strain in asymmetric rolling led to the formation of a high amount of shear bands in the microstructure of AA2024 alloy. During aging treatment at the temperature of 300 °C, recrystallization was locally started in the shear bands. The grain morphology of the rolled sample was not much changed after aging at the temperature of 190 and 300 °C. However, the samples aged at 400 and heat-treated at 500 °C had different microstructures. In addition, with increasing the temperature to 500 °C, numerous dispersoids were formed in the microstructure of the AA2024 alloy. The sample after aging treatment at 190 °C had the maximum hardness, yield strength, and ultimate tensile strength of 207.4 HV, 481.7 MPa, and 605.1 MPa, respectively, along with a desirable elongation (7.9%). By increasing the aging temperature, the hardness and strength of the alloy considerably decreased. The aging treatment at 400 and heat treatment at 500 °C led to the complete elimination of the strain hardening effect and recurrence of Portevin-Le Chatelier (PLC) in the stress-strain curves. The fracture mode was often a ductile mode for all samples. By increasing the aging temperature, the number and size of dimples increased. As a consequence, the processing technique used in the present study resulted in an excellent strength-ductility balance due to an appropriate combination of strain hardening and precipitation hardening.

2

The Effect of Heat Treatment on the Microstructure Evolution and Properties of an Age-Hardened Cu-3Ti-2Mg Alloy

Liu Jituo, Wang Xianhui, Liu Jia, Ran Qianni

Archives of Metallurgy and Materials

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2021

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Vol. 66, iss. 1

163--170

EN

The study investigates the effect of heat treatment on the microstructure evolution and properties of an age-hardened Cu-3Ti-2Mg alloy. The precipitated Cu2Mg and β'-Cu4Ti phases consequently yield a depletion of the Cu matrix in regards to Ti and Mg solutes, which enhances the electrical conductivity. The Cu2Mg Laves phase and β'-Cu4Ti phase precipitates increase the hardness of the alloy due to the consistency and coherency of the later phase. However, the decrease of hardness is mainly associated with the coarse microstructures, that can be formed due to the phase transformation from metastable β'-Cu4Ti phase to more stable Cu3Ti phase. In the range of experiments, the optimum process is solution treatment at 700°C for 4 h, with subsequent age-hardening at 450°C for 4 h. The electrical conductivity, hardness, tensile strength, and elongation of the Cu-3Ti-2Mg alloy were 15.34 % IACS, 344 HV, 533 MPa, and 12%, respectively.

3

Fabrication and Evaluation of AA6061/AA5052/AA6061/AA5052 Multi-Layer Complex Sheet by Cold-Roll Bonding Process

Lee Seong-Hee

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 3

1093--1097

EN

A cold roll bonding process is applied to fabricate an AA6061/AA5052/AA6061/AA5052multi-layer sheet. Two AA6061 and two AA5052 sheets with 2mm thickness are stacked alternately to each other, and reduced to a thickness of 2 mm by multi-pass cold rolling. The roll bonded multi-layer sheet is then hardened by natural aging (T4) and artificial aging (T6) treatments. The as roll-bonded sheet shows a typical deformation structure that the grains are elongated to the rolling direction. However, after T4 and T6 aging treatments, it has a recrystallization structure consisting of the coarse equiaxed grains in both AA5052 and AA6061 sheets. The as rolled material shows a lamella structure in which AA5052 and AA6061 sheets are stacked alternately to each other, having higher hardness in AA5052 than in AA6061. However, T4 and T6 aging treated materials show a different lamella structurein which the hardness of the AA6061 layers is higher than that of the AA5052 layers. The strengths of the T4 and T6 age-treated specimens are found to increase by 1.3 and 1.5 times respectively, compared to that of the starting material.

4

Aging Behaviour of AA6061/SiCP Composites Produced by Direct Extrusion with a Reversibly Rotating Die Method

Wozniak J., Kostecki M., Broniszewski K., Bochniak W., Olszyna A.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 3A

1755--1761

EN

This paper discusses the influence of thermal treatment parameters on mechanical properties of AA6061+x% vol. SiCp (x = 0, 2.5, 5, 7.5, 10) composites. The composites were consolidated via powder metallurgy processing using the unconventional method of extrusion (the KoBo method). In order to establish the optimum parameters of the heat treatment two different temperatures of supersaturation (530 and 558ºC) were applied. The aging curves were determined at various aging temperatures such as 140, 160, 180 and 200ºC. The effects of applied parameters were studied using the microstructure observations and hardness measurements. Obtained results show that the solution treatment at 530ºC is sufficient to complete dissolution of the precipitates. Higher temperature of the process resulted in accelerating the aged-hardening. The suitable age treating parameters for the AA6061-5 vol. % SiCp composites were 160-180ºC for 12-16 hours.

PL

W niniejszym artykule określono wpływ obróbki cieplnej na właściwości kompozytów AA6061+x% obj. SiCp (x = 0, 2.5, 5, 7.5, 10). Materiały wytwarzane były przy wykorzystaniu metalurgii proszków. W ostatnim etapie procesu technologicznego, do konsolidacji mieszanin proszków zastosowano metodę wyciskania z rewersyjnie rotująca matrycą (metoda KoBo). W celu określenie optymalnych parametrów obróbki cieplnej zastosowano dwie temperatury przesycania (530 i 558ºC) oraz cztery temperatury starzenia (140, 160, 180 and 200ºC) kompozytów. Obrabiane materiały zostały poddane obserwacjom mikrostruktury oraz wykonano pomiary twardości w celu określenia optymalnych parametrów procesów przesycania i starzenia. Na podstawie otrzymanych wyników można stwierdzić, że temperatura przesycania 530ºC jest wystarczająca do uzyskania przesyconego roztworu stałego. Ponadto określono optymalne warunki starzenia dla kompozytu AA6061-5 obj. % SiCp: temperaturę w zakresie 160 - 180ºC oraz czas starzenia 12-16 godzin.

5

Investigations of microstructure and dislocations of cast magnesium alloys

Tański T., Dobrzański L. A., Labisz K.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 42, nr 1-2

94-102

EN

Purpose: The microstructures and the dislocation arrangements in the cast magnesium alloy have been investigated using transmission electron microscopy and high-resolution transmission electron microscopy. In this paper are presented also the results of phase morphology investigation of an new developed Mg alloy. Such studies are of great interest for the metal industry, mainly the automobile industry, were the improvement of cast elements quality is crucial for economic and quality reason and depends mainly on properly performed controlling process of the production parameters. There are presented especially the effect of heat treatment on the size and distribution of the precipitation occurred in the matrix. Design/methodology/approach: The basic assumptions of this work are realised an Universal Metallurgical Simulator and Analyzer. The solidification process itself is analysed using the UMSA device by appliance of the Derivative Thermo Analysis. The thermal analysis was performed at a low but regulated cooling rate in a range of 0.2 oC to ca. 3 oC. Cooling curve for the thermal analysis was performed using a high sensitivity thermocouples of the K type, covered with a stainless steel sheath. The data were acquired by a high speed data acquisition system linked to a PC computer. Two different types of samples were used, bulk-cylindrical, and thin-walled cylindrical. Metallographic investigation were made on cross section samples of a engine bloc. Non-equilibrium heating and cooling process conditions were applied to achieve changes in shape and distribution of the phases such as Al2Cu and Si. Findings: During the investigation Dislocation networks are found to increase with deformation in all cases. The dislocation networks have been found in the g- Mg17Al12 phase as well as in the matrix in the investigation magnesium alloys. The crystallographic orientation relationship are: (1 01) .-Mg Ś (10 ) Mg17Al12 and [11 0] .-Mg Ś [111] Mg17Al12. Precipitation of the g-Mg17Al12 phase are mostly of the shape of roads, and the prevailing growing directions are the directions <110> .-Mg. Research limitations/implications: The investigations were performed using standard metallographic investigation as optical, scanning and transmission electron microscopy methods, also electron diffraction methods were applied for phase identification. Originality/value: The originality of this work is based on applying of regulated cooling rate of magnesium alloy for structure and mechanical properties changes. In this work the dependence between the regulated heat treatment, chemical composition and structure of the investigated magnesium cast alloy on the basis of the structure investigations was presented.