Influence of Thermal Aging Parameters on the Characteristics of Aluminum Semi-Solid Alloys

The current study aimed at analyzing the response of semisolid A357 aluminum alloys to unconventional thermal treatment cycles of T4/T6/T7 conditions. The mechanical, electrical, and microstructural characterizations of such semisolid alloys were investigated. The microstructure evolutions of Fe-intermetallic phases and strengthening precipitates were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The mechanical failure of such semi solid A357 aluminum alloys, used for suspension automotive parts, is mostly related to cracking issues which start from the surface due to hardness problems and propagate due to severe load variations. For these reasons, the multiple thermal aging cycles, in this study, are applied to enhance the mechanical properties and to have compromised values compared to those obtained by standard thermal treatments. The results obtained in this work indicate that the heat treatment of this alloy can be optimized. The results showed that the optimum characteristics of A357 semisolid alloys were obtained by applying thermal under-aging cycle, interrupted thermal aging cycles and a T7/T6 two steps aging treatment condition. The electrical conductivity and electron microscopy were applied in this study to analyze the characteristics of hardening phases formed due to different aging cycles applied to the alloys investigated.

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Quality Index Charts of Al-Si-Mg Semi Solid Alloys Subjected to Multiple Temperatures Aging Treatments and Different Quenching Media

Materials ◽

10.3390/ma12111834 ◽

2019 ◽

Vol 12 (11) ◽

pp. 1834 ◽

Cited By ~ 1

Author(s):

Khaled Ahmed Ragab ◽

Mohamed Bouazara ◽

X.-Grant Chen

Keyword(s):

Thermal Aging ◽

Quality Index ◽

Mechanical Performance ◽

Statistical Design ◽

Aging Treatment ◽

Statistical Design Of Experiments ◽

Quenching Media ◽

And Performance ◽

Semi Solid ◽

Solid Alloys

The use of quality index charts is considered as an effective mean for evaluating the mechanical performance of Aluminum alloys for industrial engineering applications. The current study was carried out to investigate the influences of multiple-interrupted temperatures aging and quenching media (water versus air) on the quality index performance and precipitations evolution of A357 Aluminum semi solid alloys. Regarding the lack of similar investigations applied on such alloys, the quality index charts were generated for Al-Si-Mg semi solid castings based on its tensile properties. These charts are used to determine the quality index, in MPa, as a simple mean for compromising the strength and ductility together in one value using the Drouzy model. The multiple temperatures aging cycles were applied to improve the quality index values of Al-Si-Mg semi solid alloys for enhancing its characteristic and performance to resist the mechanical failures relating to automotive dynamic parts. The evolution of Mg2Si hardening precipitates, formed for specific thermal aging cycles, was investigated using transmission electron microscopy (TEM). The results obtained in this work revealed that the optimum quality index values were obtained by the application of T6-thermal under-aging treatment cycles. The regression models, using a statistical design of experiments, indicated that the optimum strength and high-quality index values were obtained by the application of interrupted thermal aging cycles, mainly C2,3-T6/T4/T7 conditions.

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Influences of Carbon and Nitrogen Content on the Precipitation of 18Cr18Mn Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.789.297 ◽

2014 ◽

Vol 789 ◽

pp. 297-302

Author(s):

Jing Yuan Li ◽

Fei Fang ◽

Yi De Wang ◽

Bo Li ◽

Xiang Jun Zhang

Keyword(s):

Electron Microscopy ◽

Cast Steel ◽

Austenitic Stainless Steels ◽

Aging Treatment ◽

Solidification Process ◽

Σ Phase ◽

Carbon And Nitrogen ◽

Transmission Electron ◽

Carbon And Nitrogen Content ◽

Nitrogen Contents

The effect of carbon and nitrogen contents on microstructure and the mechanism of precipitation of 18Cr18Mn steels at as-cast and aging treatment state were investigated by thermodynamics calculation, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results show that the increase in carbon and nitrogen contents promotes the precipitation of carbides and nitrides, respectively, inhibiting σ phase precipitation during solidification process. The rod-like σ phases present in 18Cr18Mn0.44N as-cast steel with 0.025%C. The coarse lamellar structure Cr23C6 phases with a space width of 0.34μm exist in 18Cr18Mn0.44N as-cast steel with 0.16%C. However, Cr23C6 and σ phase disappear in the interior of the grains and a small amount of nitrides exist only in grain boundaries of 18Cr18Mn0.72N0.020C as-cast steel. The precipitation of Cr23C6 and σ phases are greatly inhibited in high nitrogen austenitic stainless steels at 800°C aging treatment. Additionally, Cr2N, the main precipitation phase, nucleates at austenitic grain boundary and grows towards inner grains with a lamellar morphology. Moreover, the quantity of Cr2N increases and incubation time of it decreases as nitrogen or carbon content increasing.

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A Weak-Beam Dark-Field Study of Stacking Faults in a Co-Cr-Mo-C Alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100091871 ◽

1976 ◽

Vol 34 ◽

pp. 378-379

Author(s):

Ernest L. Hall

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Field Study ◽

Previous Investigation ◽

Stacking Faults ◽

Aging Treatment ◽

Dark Field ◽

Bright Field ◽

Weak Beam ◽

Transmission Electron

In a previous investigation (1) of the mechanisms of strengthening in a Co-28 wt% Cr-6 wt% Mo-0.29 wt% C alloy (H.S. 21), it was observed that the fee regions of this alloy were generally heavily faulted, and the density of stacking faults was seen to be dependent upon the time and temperature of the aging treatment after solutionizing. In the present study, weak-beam darkfield transmission electron microscopy was used to examine the interaction of stacking faults on intersecting {111} planes. The alloy was solutionized at 1230°C for 4 hours, quenched in water, and aged at 650°C for 8 hours in order to produce a suitable density of faults. Figure 1 shows a bright-field (BF), weak-beam dark-field (WB DF) pair of micrographs illustrating both the successful and unsuccessful intersection of faults which exist in different ﹛111﹜ planes.

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TEM/STEM Characterization of Rapidly Solidified Aluminum Alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117236 ◽

1985 ◽

Vol 43 ◽

pp. 30-31

Author(s):

R. J. Kar ◽

T. P. McHale ◽

R. T. Kessler

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Aluminum Alloys ◽

High Strength ◽

Advanced Materials ◽

Structure Property ◽

Aerospace Applications ◽

Transmission Electron ◽

Scanning Transmission ◽

Rapidly Solidified

Low-density and high strength-type rapidly solidified (RST) aluminum alloys offer promise for structural aerospace applications. At Northrop, as part of a continuing program to establish structure-property relationships in advanced materials, detailed transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) of candidate RST aluminum-lithium (Al-Li) and high strength (7XXX-type) aluminum-copper-magnesium-zinc (Al-Cu-Mg-Zn) alloys is routinely performed. This paper describes typical microstructural features that we have observed in these alloys.Figure 1 illustrates the microstructure of an inert-gas atomized RST Al-Li-Cu-Mg-Zr alloy. Frequently the grain boundaries are decorated with continuous or semi-continuous stringers of oxide that are relatively opaque to the incident electron beam. These have been identified to be Al-,Mg-, and Li- containing oxides present on powder particle surfaces prior to consolidation, and which have not been adequately broken up and dispersed by post-consolidation processing. The microstructures of these alloys are generally characterized by unrecystallized grains and equiaxed sub-grains pinned by fine (0.2μm) precipitates. These have been identified to be Al3Zr dispersoids using a combination of selected area diffraction/energy-dispersive x-ray (SAD/EDX) methods.

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Using Recycled Materials for Semi- Solid Processing of Al-Si-Mg Based Alloys

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.327.207 ◽

2022 ◽

Vol 327 ◽

pp. 207-222

Author(s):

Jiehua Li ◽

Xun Zhang ◽

Johannes Winklhofer ◽

Stefan Griesebner ◽

Bernd Oberdorfer ◽

...

Keyword(s):

Electron Microscopy ◽

Shape Factor ◽

Volume Fraction ◽

Solidification Microstructure ◽

Number Density ◽

Foundry Industry ◽

Transmission Electron ◽

Eutectic Si ◽

Semi Solid ◽

Secondary Materials

In order to reduce CO2 emission and energy consumption, more recycled secondary materials have to be used in foundry industry, especially for Al-Si-Mg based alloys for semi-solid processing. In this paper, Al-Si-Mg based alloys with the addition of recycled secondary materials up to 30 % (10, 20, 30 %, respectively) have been produced by semi-solid processing. The solidification microstructure was investigated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, computed tomography (CT) was also used to elucidate the size, size distribution, number density, volume fraction of porosities. It was found that with the addition of the recycled secondary materials up to 30 %, there is no significant effect on the solidification microstructure in terms of the grain size and the shape factor of primary α-Al and the second α-Al. More importantly, the morphology of eutectic Si can be well modified and that of the Fe-containing phase (π-AlSiMgFe) can be tailored. Furthermore, with increasing recycled secondary materials, at least another two important issues should also be highlighted. Firstly, more TiB2 particles were observed, which can be due to the addition of Al-Ti-B grain refiners for the grain refinement of recycled secondary materials. Secondly, a significant interaction between Sr and P was also observed in the recycled secondary materials. The present investigation clearly demonstrates that Al-Si-Mg based alloys with the addition of recycled secondary materials at least up to 30% can be used for semi-solid processing, which may facilitate better sustainability.

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Aging Behavior of Semi-Solid Mg-10Al-0.3Mn Alloy by the Hot Extrusion

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.658.102 ◽

2013 ◽

Vol 658 ◽

pp. 102-107

Author(s):

Dae Hwan Kim ◽

Heek Yung Kim ◽

Su Gun Lim

Keyword(s):

Aging Treatment ◽

Hot Extrusion ◽

Hardness Test ◽

Tensile Tests ◽

Conductivity Measurements ◽

Aging Behavior ◽

Transmission Electron ◽

Aging Conditions ◽

Ram Speed ◽

Semi Solid

In present study, the aging behavior of the hot extruded semi-solid Mg-10Al-0.3Mn alloy was investigated. In order to obtain the extruded bar, we carried out the hot extrusion at 380°C with an extrusion ratio of 25 and ram speed of 2.4mms-1. Vickers hardness test, electrical conductivity measurements, scanning and transmission electron microscopy and tensile testing were performed to identify the aging behaviors and mechanical properties during the aging treatment. Observations of the aging behavior and results of the tensile tests after the T6 heat treatment at each aging temperature show that the optimum aging conditions was indicated by a hardness increment of 72% and a tensile strength of 340MPa in the extruded bar.

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Optimal Filling of Test Dies for Evaluating Properties of Semi-Solid Alloys

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.116-117.145 ◽

2006 ◽

Vol 116-117 ◽

pp. 145-148

Author(s):

Chee Ang Loong ◽

Chang Qing Zheng

Keyword(s):

Electron Microscopy ◽

Mechanical Properties ◽

A356 Alloy ◽

Flow Patterns ◽

Optical And Electron Microscopy ◽

Semi Solid ◽

The Moment ◽

Alloy Segregation ◽

Solid Alloys ◽

Filling And Solidification

An investigative study was conducted on how two different dies designed to produce sound specimens for evaluating mechanical properties of semi-solid alloys could be filled optimally. The first die contains one cavity that produces a wedge with a sectional thickness varying from 19.05 mm (0.75 in) to 9.52 mm (0.375 in). The second die contains four cavities fed by a single runner, producing ASTM-type round bars with a diameter of 9.52 mm (0.375 in). Experiments were undertaken to cast partial and complete shots of A356 alloy test specimens under controlled injection conditions. Flow patterns developed from the moment the alloy entered the cavity were noted, including difficulties experienced in balancing flow in the four-cavity die. Microstructural abnormalities were observed in the bar specimens examined using optical and electron microscopy. It was found that control of filling and solidification in the wedge die was much easier and specimens produced did not result in any significant alloy segregation.

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