Nano-Scale Clusters Formed in the Early Stage of Phase Decomposition of Al-Mg-Si Alloys

2005 ◽  
Vol 475-479 ◽  
pp. 357-360 ◽  
Author(s):  
Shoichi Hirosawa ◽  
Tatsuo Sato
Keyword(s):  
Early Stage ◽  
Sheet Material ◽  
Three Dimensional ◽  
Natural Aging ◽  
Aging Treatment ◽  
Atom Probe ◽  
Phase Decomposition ◽  
Aging Behavior ◽  
Scanning Calorimetry ◽  
Nano Scale

The formation of nano-scale clusters (nanoclusters) prior to the precipitation of the strengthening b” phase significantly influences two-step aging behavior of Al-Mg-Si alloys. In this work, the existence of two kinds of nanoclusters has been verified in the early stage of phase decomposition by differential scanning calorimetry (DSC) and three-dimensional atom probe (3DAP). Pre-aging treatment at 373K before natural aging was also found to form preferentially one of the two nanoclusters, resulting in the remarkable restoration of age-hardenability at paint-bake temperatures. Such microstructural control by means of optimized heat-treatments; i.e. nanocluster assist processing (NCAP), possesses great potential for enabling Al-Mg-Si alloys to be used more widely as a body-sheet material of automobiles.

Aging Behavior of Cu-Ni-Si Alloy Processed by High-Pressure Torsion

2010 ◽  
Vol 667-669 ◽  
pp. 307-312 ◽  
Author(s):  
Hirotaka Matsunaga ◽  
Z. Horita ◽  
Kazutaka Imamura ◽  
Takanobu Kiss ◽  
Xavier Sauvage
Keyword(s):  
Electrical Conductivity ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Three Dimensional ◽  
Aging Treatment ◽  
Atom Probe ◽  
Appreciable Amount ◽  
Aging Behavior ◽  
Transmission Electron ◽  
20 Nm

An age-hardenable Cu-2.9%Ni-0.6%Si alloy was subjected to high-pressure torsion. Aging behavior was investigated in terms of hardness, electrical conductivity and microstructural features. Transmission electron microscopy showed that the grain size is refined to ~150 nm and the Vickers microhardness was significantly increased through the HPT process. Aging treatment of the HPT-processed alloy led to a further increase in the hardness. Electrical conductivity is also improved with the aging treatment. It was confirmed that the simultaneous strengthening by grain refinement and fine precipitation is achieved while maintaining high electrical conductivity. Three dimensional atom probe analysis revealed that fine precipitates with sizes of ~20 nm or smaller were formed in the Cu matrix and some particles consist of Ni and Si with no appreciable amount of Cu.

3DAP Characterization and Thermal Stability of Nano-Scale Clusters in Al-Mg-Si Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 245-250 ◽  
Author(s):  
Ai Serizawa ◽  
Shoichi Hirosawa ◽  
Tatsuo Sato
Keyword(s):  
Thermal Stability ◽  
Quantitative Estimation ◽  
Three Dimensional ◽  
Atom Probe ◽  
Chemical Compositions ◽  
Scanning Calorimetry ◽  
Subsequent Formation ◽  
Nano Scale ◽  
Β Phase ◽  
Cluster 2

The formation of nano-scale clusters (nanoclusters) prior to the precipitation of the strengthening β" phase significantly influences the two-step aging behavior of Al-Mg-Si alloys. In this work, two types of nanoclusters are found to be formed at different temperatures. The characterization of these two nanoclusters has been performed from the viewpoints of composition and thermal stability using a three-dimensional atom probe (3DAP) and differential scanning calorimetry (DSC). Mg-Si co-clusters formed at room temperature (RT), Cluster(1), play a deleterious role in the subsequent formation of the β" phase because of the high thermal stability even at the bake-hardening (BH) temperature of 443K. In contrast, the nanoclusters formed by pre-aging at 373K, Cluster(2), are effective in the formation of the refined β", suggesting that Cluster(2) transforms more easily into the β" phase than Cluster(1). The quantitative estimation of the chemical compositions of the two nanoclusters suggests that the Mg/Si ratio is one of the key factors in addition to the internal structures consisting of Si, Mg and probably vacancies. The detailed two-step aging mechanism in Al-Mg-Si alloys is proposed based on the characteristics of the two types of nanoclusters.

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

2014 ◽  
Vol 794-796 ◽  
pp. 897-902 ◽  
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.

scholarly journals T4 and T6 Treatment of 6061 Al-15 Vol. % SiCP Composite

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
S. Rajasekaran ◽  
N. K. Udayashankar ◽  
Jagannath Nayak
Keyword(s):  
Room Temperature ◽  
Artificial Aging ◽  
Brinell Hardness ◽  
Natural Aging ◽  
Aging Treatment ◽  
Temperature History ◽  
Peak Hardness ◽  
Aging Behavior ◽  
Hardness Variation ◽  
Peak Aging

Aging temperature history has profound effect on the mechanical and corrosion behavior of 6061 Al/SiC composite. In order to understand the effect of aging on the corrosion resistance, the natural and artificial aging behavior of 15 vol. % 6061 Al-SiCP composites was studied using the aging treatment and the Brinell hardness measurements. The aging curves for the composite (T6 treated) were determined at various aging temperatures such as room temperature, 140, 160, 180, 200, 220, and 240°C. According to the peak hardness variation with temperature profile, it is found that the composite is underaged at 140°C and 160°C. Peak aging takes place at 180°C. Overaging takes place at 200°C, 220°C, and 240°C. The natural aging characteristics of the composite (T4 treated) are also studied using the Brinell hardness measurements.

Atom probe study of early stage phase decomposition in an Al-7.8 at.% Li alloy

1992 ◽  
Vol 40 (11) ◽  
pp. 3027-3034 ◽  
Author(s):  
K. Hono ◽  
S.S. Babu ◽  
K. Hiraga ◽  
R. Okano ◽  
T. Sakurai
Keyword(s):  
Early Stage ◽  
Atom Probe ◽  
Phase Decomposition

Effects of Zn Addition and Aging Condition on Serrated Flow in Al-Mg Alloys

2014 ◽  
Vol 794-796 ◽  
pp. 483-488 ◽  
Author(s):  
Katsushi Matsumoto ◽  
Yasuhiro Aruga ◽  
Hidemasa Tsuneishi ◽  
Hikaru Iwai ◽  
Masataka Mizuno ◽  
...  
Keyword(s):  
Artificial Aging ◽  
Flow Behavior ◽  
Natural Aging ◽  
Atom Probe ◽  
Mg Alloys ◽  
Scanning Calorimetry ◽  
Serrated Flow ◽  
Zn Addition ◽  
Al Mg Alloys ◽  
Zn Alloys

The serrated flow phenomena in Al-Mg alloys with and without Zn were investigated after aging on several conditions, focusing on the role of precipitates. Al-6mass%Mg-0~3mass%Zn alloys were solution treated at 753~803K, quenched, and then aged at room temperature. Further artificial aging at 323~573K for 86.4ks was performed for some of them after natural aging for 2.6Ms. The serrated flow behavior was evaluated by tensile test. Microstructure was characterized by differential scanning calorimetry, transmission electron microscopy, atom probe tomography, and positron annihilation lifetime spectroscopy. The increase in the amount of Zn addition and the natural aging time lead to a delayed onset of serrated flow. The artificial aging at higher temperatures after natural aging, on the other hand, decreases the onset strain. A large number of small coherent Zn-Mg clusters are formed during natural aging in the Al-Mg-Zn alloys, which are transformed to the larger incoherent meta-stable precipitates during subsequent artificial aging. These results suggest that the mechanism of interfering with serrated flow is related to the vacancy trapping effect, which is enhanced by the coherent clusters.

Nanoscale Precipitation in a Maraging Steel Studied by APFIM

2004 ◽  
Vol 10 (3) ◽  
pp. 342-348 ◽  
Author(s):  
Krystyna Stiller ◽  
Mats Hättestrand
Keyword(s):  
Maraging Steel ◽  
Material Properties ◽  
Three Dimensional ◽  
Atom Probe ◽  
Chemical Information ◽  
Phase Decomposition ◽  
Precipitation Sequence ◽  
Rich Phase ◽  
Complementary Methods ◽  
Prolonged Aging

This article summarizes findings from our previous investigations and recent studies concerning precipitation in a maraging steel of type 13Cr-9Ni-2Mo-2Cu (at.%) with small additions of Ti (1 at.%) and Al (0.7 at.%). The material was investigated after aging at 475°C up to 400 h using both conventional and three-dimensional atom-probe analyses. The process of phase decomposition in the steel proved to be complicated. It consisted of precipitation of several phases with different chemistry. A Cu-rich phase was first to precipitate and Mo was last in the precipitation sequence. The influence of the complex precipitation path on the material properties is discussed. The investigation clearly demonstrated the usefulness of the applied techniques for investigation of nanoscale precipitation. It is also shown that, complementary methods (such as TEM and EFTEM) giving structural and chemical information on a larger scale must be applied to explain the good properties of the steel after prolonged aging.

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