Effects of Pre-Aging and Natural Aging on Bake Hardening Behavior in Al-Mg-Si Alloys

The effects of pre-aging and natural aging on the bake hardening behavior of Al-0.62Mg-0.93Si (mass%) alloy with multi-step aging process were investigated by means of Vickers hardness test, tensile test, differential scanning calorimetry analysis (DSC) and transmission electron microscopy (TEM). The characteristics of nanoclusters (nano scale solute atom clusters) formed during pre-aging and natural aging were also investigated using the three dimensional atom probe (3DAP) analysis. The results revealed the occurrence of natural age hardening and that the bake hardening response was decreased after the extended natural aging even though the pre-aging was conducted before natural aging. Since the 3DAP results exhibited the Si-rich clusters were newly formed during extended natural aging, it was assumed that the Si-rich clusters caused the natural age hardening and the reduced bake hardening response corresponding to Cluster(1). The decrease of the bake hardening response was markedly higher in the later stage of bake hardening than in the early stage. The size of the β’’ precipitates were reduced with increasing the natural aging time. Exothermic peaks of Peak 2 and Peak 2’ were observed in the DSC curves for the alloys pre-aged at 363K. Peak 2’ became larger with the natural aging time. This is well understood by the following model. The transition from Cluster(2) to the β’’ phase occurs preferentially at the early stage of the bake hardening. Then the growth of the β’’ phase is inhibited by the presence of Cluster(1) at the later stage of bake hardening. The combined formation of Cluster(1) and Cluster(2) by the multi-step aging essentially affects the bake hardening response and the β’’ precipitates in the Al-Mg-Si alloys.

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Effects of Mg Addition and Pre-Aging on the Age-Hardening Behavior in Al-Mg-Si

Metals ◽

10.3390/met8121046 ◽

2018 ◽

Vol 8 (12) ◽

pp. 1046 ◽

Cited By ~ 1

Author(s):

JaeHwang Kim ◽

Jiwoo Im ◽

Minyoung Song ◽

Insu Kim

Keyword(s):

Early Stage ◽

Natural Aging ◽

Age Hardening ◽

Number Density ◽

Hardening Behavior ◽

Transmission Electron ◽

Alloy Hardness ◽

Peak Aged ◽

Mg Addition ◽

Cluster 2

Two types of nanoclusters, Cluster (1) and Cluster (2), formed at around room temperature and 100 °C, respectively, affect the age-hardening behavior in Al-Mg-Si alloys. Formation of Cluster (1) during natural aging (NA) is more accelerated in the high-Mg (9M10S) alloy than in the low-Mg (3M10S) alloy. Hardness at the early stage of two-step aging at 170 °C is not increased for the natural aging samples. On the other hand, hardness is directly increased for the pre-aged (PA) specimens. Furthermore, the formation of Cluster (1) during natural aging is suppressed by the formation of Cluster (2) during pre-aging at 100 °C. To understand the effects of heat treatment histories and Mg contents on the microstructure, transmission electron microscopy (TEM) was utilized. All the images were obtained at (001) plane, and peak aged samples with different heat treatments were used. Lower number density of precipitates is confirmed for the natural aging samples compared with the single-aged and pre-aged specimens. A higher number density of precipitates is confirmed for 9M10S in comparison to 3M10S. Hardness results correspond well to the TEM images.

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Effect of Combined Pre-Straining and Pre-Aging on the Precipitation Behavior and Age Hardening Response for Al-Mg-Si Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1026.74 ◽

2021 ◽

Vol 1026 ◽

pp. 74-83

Author(s):

Guan Jun Gao ◽

Xi Wu Li ◽

Li Zhen Yan

Keyword(s):

Electron Microscopy ◽

Natural Aging ◽

Hardness Test ◽

Age Hardening ◽

Precipitation Behavior ◽

Strengthening Phase ◽

Scanning Calorimetry ◽

Transmission Electron ◽

Hardening Treatment ◽

Cluster 2

Pre-strain (PS) and pre-aging (PA) treatments are often applied during the preparation of Al-Mg-Si automotive aluminum alloy. In this study, the effect of combined PS and PA on the precipitation behavior and age hardening response for Al-Mg-Si alloys was investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile test, Vickers hardness test, and differential scanning calorimetry (DSC). It was found that the dislocations introduced by PS treatment and the cluster (2) formed during PA treatment effectively inhibited the cluster (1), which further strengthened the inhibition of natural aging hardening at room temperature (RT). The strength increment of the alloys was kept below 10.0 MPa during two weeks RT storage. The dislocations provided heterogeneous nucleation for the precipitates forming and the cluster (2) transformed into β″ strengthening phase during bake hardening treatment. With the acceleration response of the dislocations and the cluster (2), the age hardening response of Al-Mg-Si alloys obviously improved with the denser and larger β″ strengthening phase formed.

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Effects of Isothermal Aging on Clustering and Paint-Bake Hardening Behavior in an Al-Mg-Si Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.794-796.897 ◽

2014 ◽

Vol 794-796 ◽

pp. 897-902 ◽

Cited By ~ 1

Author(s):

Yasuhiro Aruga ◽

Masaya Kozuka ◽

Yasuo Takaki ◽

Tatsuo Sato

Keyword(s):

Early Stage ◽

Natural Aging ◽

Atom Probe ◽

Bake Hardening ◽

Subsequent Aging ◽

Significant Drop ◽

Β Phase ◽

Long Time ◽

Hardness Increase ◽

Small Clusters

The relationship between the cluster morphology formed during natural or artificial aging and the paint-bake hardening response in an Al-0.62Mg-0.93Si (mass%) alloy have been investigated using atom probe tomography (APT). Increasing the subsequent aging time at 170 °C causes a gradual increase in hardness in the artificially aged materials, while the retardation period of the hardness increase appears in the naturally aged materials at the early stage of aging. The statistically-proved records in the APT analysis have shown that the artificially aged materials have some large clusters. It is revealed that the hardening at the early stage of the subsequent aging at 170 °C is not promoted in the long-time naturally aged material although the number density of small clusters increases approximately 1.3 times by prolonged natural aging.Hence, we believe that the small clusters are hard to transform continuously into the β'' phase during aging at 170 °C. As for the naturally aged materials, the long-time aging leads to a significant drop in hardness at the early stage of aging at 170 °C. It is speculated that the Mg-Si mixed clusters formed after long-time natural aging can be reversed during the subsequent heat treatment.

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TEM Observation for Precipitates Structure of Al-1.0Mass%Mg2Ge Alloys Aged at 473K

Materials Science Forum ◽

10.4028/www.scientific.net/msf.794-796.992 ◽

2014 ◽

Vol 794-796 ◽

pp. 992-995

Author(s):

Akihiro Kawai ◽

Keisuke Matsuura ◽

Katsumi Watanabe ◽

Kenji Matsuda ◽

Susumu Ikeno

Keyword(s):

Phase Diagram ◽

Equilibrium Phase ◽

Hardness Test ◽

Age Hardening ◽

Precipitation Sequence ◽

Hardening Behavior ◽

Β Phase ◽

Hrtem Observation ◽

Peak Aged ◽

First Time

It is known that Al-Mg-Ge alloys show a similar precipitation sequence to that of Al-Mg-Si alloys, and that ther equilibrium phase is β-Mg2Ge according to the phase diagram. In this study, the precipitation sequence and age-hardening behavior of Al-1.0mass%Mg2Ge alloys has been investigated by hardness test, write out in full first time used TEM and HRTEM observations on.The hardness curves showed no big difference between peak values hardness for samples aged at 423, 473 and 523K. The precipitates in the peak-aged samples have been classified as some metastable phases, such as the β’-phase and parallelogram-type precipitates by HRTEM observation. The large precipitates are similar to the A-type precipitate in the Al-Mg-Si alloy with excess Si.

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Aging Behavior of Al-Mg-Ge Alloys with Different Mg2Ge Contents

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.409.63 ◽

2011 ◽

Vol 409 ◽

pp. 63-66

Author(s):

Tomoatsu Murakami ◽

Kenji Matsuda ◽

Takeshi Nagai ◽

Junya Nakamura ◽

Tokimasa Kawabata ◽

...

Keyword(s):

Relative Frequency ◽

Equilibrium Phase ◽

Hardness Test ◽

Age Hardening ◽

Precipitation Sequence ◽

Aging Behavior ◽

Hardening Behavior ◽

Β Phase ◽

Hrtem Observation ◽

Peak Aged

It is known that Al-Mg-Ge alloy shows the similar precipitation sequence to Al-Mg-Si alloy, and its equilibrium phase is β-Mg2Ge according to its phase diagram. In this study, the precipitation sequence of Al-Mg-Ge alloys containing different contents of Mg2Ge has been investigated by hardness test, TEM and HRTEM observation to understand the effect of Mg2Ge contents on age-hardening behavior of the alloys. The hardness of as-quenched and peak-aged samples have been improved by increasing Mg2Ge contents. The precipitates in the peak-aged samples have been classified into some metastable phases, such as the β’-phase and parallelogram-type precipitate by HRTEM observation. The relative frequency of these precipitates in the is has been changed with Mg2Ge contents.

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Age-Hardening Behavior of Pd-Ag-Sn-In-Zn Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1028.14 ◽

2014 ◽

Vol 1028 ◽

pp. 14-19 ◽

Cited By ~ 2

Author(s):

Hai Jun Wu ◽

Xiao Qing Zuo ◽

Ying Wu Wang ◽

Kun Hua Zhang ◽

Yu Zeng Chen

Keyword(s):

Aging Time ◽

Early Stage ◽

Energy Dispersive Spectrometer ◽

Hardness Test ◽

Age Hardening ◽

Aged Alloy ◽

X Ray Diffraction ◽

Electron Microscopic ◽

Scanning Electron Microscopic ◽

Zn Alloy

Pd-Ag-Sn-In-Zn alloy was subjected to isothermal aging treatments at 400°C, 500°C, and 650°C. Age-hardening behaviour and related microstructure changes of the aged alloy were studied by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) and energy dispersive spectrometer (EDS). The results indicate that the hardness of the alloy reaches a highest value of 348Hv after aging at 650°C for 20min. Further increasing the aging time leads to softening. The hardening of the alloy at early stage of the age-hardening at 650°C is ascribed to the formation of lamellar (α1+ β) precipitates along the grain boundaries of α matrix. The softening of the alloy occurred by further increasing aging time is caused by the coarsening of the precipitates.

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HRTEM Observation of the Age Hardening Precipitates in Mg-15wt%Gd-Zr Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.15-17.445 ◽

2006 ◽

Vol 15-17 ◽

pp. 445-448 ◽

Cited By ~ 1

Author(s):

Toshiyuki Matsuno ◽

Tokimasa Kawabata ◽

Kenji Matsuda ◽

Shigeharu Kamado ◽

Yo Kojima ◽

...

Keyword(s):

Aging Time ◽

Precipitation Hardening ◽

Early Stage ◽

Atomic Layer ◽

Age Hardening ◽

Β Phase ◽

Hrtem Observation ◽

Zr Alloy

The TEM observation was performed to investigate the precipitation hardening in Mg-Gd-Zr alloy. Both the β’ and the β” phase coexist in the specimen aged at 473K for 16h. In the specimen aged at 523K, the β’ phase which has base centered orthorhombic (bco) structure was observed at early stage during aging. The β’ phase has a globular shape and four atomic layer periodicity in the [1100]Mg. The β’ phase grew with increasing aging time mainly along the [0001]Mg and the [1100]Mg.

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Effects of Sn Addition on Clustering and Age-Hardening Behavior in a Pre-Aged Al-Mg-Si Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.877.455 ◽

2016 ◽

Vol 877 ◽

pp. 455-460 ◽

Cited By ~ 6

Author(s):

Hisao Shishido ◽

Yasuo Takaki ◽

Masaya Kozuka ◽

Katsushi Matsumoto ◽

Yasuhiro Aruga

Keyword(s):

Cluster Formation ◽

Natural Aging ◽

Atom Probe ◽

The Other ◽

Endothermic Peak ◽

Age Hardening ◽

Number Density ◽

Scanning Calorimetry ◽

Hardening Behavior ◽

Other Hand

The effects of Sn addition on clustering and age-hardening behavior in an Al-0.6Mg-1.0Si (mass %) alloy were investigated. Addition of Sn delayed the age-hardening in single aging at 170 ̊C. On the other hand, Sn promoted the age-hardening response in 3-step aging process which comprises a pre-aging (PA) at 90 ̊C for 18ks followed by natural aging (NA) for 604.8ks and artificial aging (AA) at 170 ̊C. The characteristics of clusters formed during PA and NA were evaluated by differential scanning calorimetry (DSC) analysis and atom probe tomography (APT). The DSC results show that the endothermic peak at around 160 ̊C to 200 ̊C was observed in the Sn-free alloy. On the other hand, in the Sn-added alloy, endothermic peak was not observed. It is suggested that Sn addition suppresses the formation of the clusters formed during NA. The APT results show that the Sn addition decreases the number density of clusters, especially smaller clusters. No Sn precipitates were found in Mg-Si precipitates formed during AA at 170 ̊C for 3.6ks. It is speculated that suppression of smaller cluster formation by addition of Sn promotes the age-hardening response

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Effect of Casting Method and Al Contents on Microstructure in AM-Type Magnesium Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.663 ◽

2010 ◽

Vol 654-656 ◽

pp. 663-666 ◽

Cited By ~ 5

Author(s):

Katsumi Watanabe ◽

Kenji Matsuda ◽

Takumi Gonoji ◽

Tokimasa Kawabata ◽

Katsuya Sakakibara ◽

...

Keyword(s):

Magnesium Alloys ◽

Hardness Test ◽

Al Alloys ◽

Age Hardening ◽

Casting Method ◽

Absorption Properties ◽

Al Content ◽

Hardening Behavior ◽

The Difference ◽

Impact Absorption

Magnesium alloys have received considerable attention because of their lightweight and recyclability. AM-type and AZ-type Mg-Al alloys have been used for industrial products widely, particularly for AM-type alloys because of the better toughness and impact absorption properties than AZ-type alloys. However, there is little report about the effect of casting method on age-hardening behavior and microstructure of AM-type alloys. The purpose of this study is to investigate the difference of the age-hardening behavior and microstructures of three AM-type alloys cast with steel, copper and sand molds using hardness test and scanning electron microscopy (SEM) observation. Furthermore, the effect of Al content is also investigated in this study using three alloys of AM30 (3%Al), AM60 (6%Al) and AM90 (9%Al).

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