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.

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

2014 ◽  
Vol 794-796 ◽  
pp. 1026-1031 ◽  
Author(s):  
Yasuo Takaki ◽  
Yasuhiro Aruga ◽  
Masaya Kozuka ◽  
Tatsuo Sato
Keyword(s):  
Aging Time ◽  
Early Stage ◽  
Natural Aging ◽  
Hardness Test ◽  
Age Hardening ◽  
Bake Hardening ◽  
Scanning Calorimetry ◽  
Hardening Behavior ◽  
Β Phase ◽  
Cluster 2

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.

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.

Effect of Aging Precipitates on the Bendability of an Al-Mg-Si Alloy

2014 ◽  
Vol 794-796 ◽  
pp. 572-577 ◽  
Author(s):  
Hidetaka Nakanishi ◽  
Mineo Asano ◽  
Hideo Yoshida
Keyword(s):  
Shear Bands ◽  
Natural Aging ◽  
Bending Test ◽  
Heat Radiation ◽  
Plate Material ◽  
Bake Hardening ◽  
Β Phase ◽  
Phase Precipitate ◽  
Aging Conditions ◽  
Better Than

Al-Mg-Si alloys are usually applied a T4 temper as the plate material for automobile bodies due to the necessity of a high bake hardening property. Many reports about the improvement in the bendability of Al-Mg-Si alloys applied a T4 temper have been published, because they easily crack during the hemming process. On the other hand, Al-Mg-Si alloys applied T6 and T7 tempers are used as the material of wiring plates and heat radiation devices. A high electrical conductivity and good bendability are necessary for these devices. In this study, the effect of the aging conditions on the bendability was investigated. As a result, the bendability at the T6 temper significantly decreased. The bendability under the aging temper, and over the aging temper was better than that at the T6 temper. Samples treated by natural-aging at high temperature before the T6 temper easily cracked during the bending test. It was postulated that the formation of shear bands was significant and the bendability decreased during the bending test under the high density and fine β phase precipitate conditions.

Hopf bifurcation for a discontinuous HTLV-1 model

Filomat ◽  
2017 ◽  
Vol 31 (20) ◽  
pp. 6247-6267 ◽  
Author(s):  
Elham Shamsara ◽  
Zahra Afsharnezhad ◽  
Reihaneh Mostolizadeh
Keyword(s):  
Hopf Bifurcation ◽  
Sliding Mode ◽  
Early Stage ◽  
Time Lag ◽  
Discontinuous System ◽  
Steady State Condition ◽  
Ctl Response ◽  
Optimal Drug ◽  
Long Time ◽  
Immunosuppressive Diseases

Developing accurate mathematical models for host immune response in immunosuppressive diseases such as HIV and HTLV-1 are essential to achieve an optimal drug therapy regime. Since for HTLV-1 specific CTL response typically occurs after a time lag, we consider a discontinuous response function to better describe this lagged response during the early stage of the infectious, thus the system of HTLV-1 model will be a discontinuous system. For analyzing the dynamic of the system we use Filippov theory and find conditions in which the Filippov system undergoes a Hopf bifurcation. The Hopf bifurcation help us to find stable and unstable periodic oscillations and can be used to predict whether the CTL response can return to a steady state condition. Also, Hopf bifurcation in sliding mode is investigated. In this case the solutions will remain in the hyper-surface of discontinuity and as a consequence the disease cannot progress, at least for a long time. Finally we use numerical simulations to demonstrate the results by example.

scholarly journals The macroscopic shape of assemblies formed from microparticles based on host–guest interaction dependent on the guest content

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Takahiro Itami ◽  
Akihito Hashidzume ◽  
Yuri Kamon ◽  
Hiroyasu Yamaguchi ◽  
Akira Harada
Keyword(s):  
Molecular Recognition ◽  
Smart Materials ◽  
Self Assembly ◽  
Early Stage ◽  
Contact Point ◽  
Sodium Acrylate ◽  
Contact Points ◽  
Assembly Behavior ◽  
Small Clusters ◽  
Macroscopic Shape

AbstractBiological macroscopic assemblies have inspired researchers to utilize molecular recognition to develop smart materials in these decades. Recently, macroscopic self-assemblies based on molecular recognition have been realized using millimeter-scale hydrogel pieces possessing molecular recognition moieties. During the study on macroscopic self-assembly based on molecular recognition, we noticed that the shape of assemblies might be dependent on the host–guest pair. In this study, we were thus motivated to study the macroscopic shape of assemblies formed through host–guest interaction. We modified crosslinked poly(sodium acrylate) microparticles, i.e., superabsorbent polymer (SAP) microparticles, with β-cyclodextrin (βCD) and adamantyl (Ad) residues (βCD(x)-SAP and Ad(y)-SAP microparticles, respectively, where x and y denote the mol% contents of βCD and Ad residues). Then, we studied the self-assembly behavior of βCD(x)-SAP and Ad(y)-SAP microparticles through the complexation of βCD with Ad residues. There was a threshold of the βCD content in βCD(x)-SAP microparticles for assembly formation between x = 22.3 and 26.7. On the other hand, the shape of assemblies was dependent on the Ad content, y; More elongated assemblies were formed at a higher y. This may be because, at a higher y, small clusters formed in an early stage can stick together even upon collisions at a single contact point to form elongated aggregates, whereas, at a smaller y, small clusters stick together only upon collisions at multiple contact points to give rather circular assemblies. On the basis of these observations, the shape of assembly formed from microparticles can be controlled by varying y.

Evolution of Nanostructure during the Early Stages of Ageing in Al-Zn-Mg-Cu Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 555-560 ◽  
Author(s):  
Peter V. Liddicoat ◽  
Tomoyuki Honma ◽  
L.T. Stephenson ◽  
Simon P. Ringer
Keyword(s):  
Atom Probe Tomography ◽  
Atom Probe ◽  
Age Hardening ◽  
Peak Hardness ◽  
Cu Alloys ◽  
Transmission Electron ◽  
Element Species ◽  
Hardness Increase ◽  
Solute Interactions ◽  
Effect Of Copper

During age-hardening of certain Al-Zn-Mg-Cu alloys, a 90% hardness increase can occur with 75 seconds. The clustering and precipitation of solute element species during this early rapid hardening (RH) period has been investigated through atom probe tomography, transmission electron microscopy, and Vickers hardness measurements. This study has focussed on the effect of copper by analysing three alloys; Al-2.0Zn-1.8Mg-0.7Cu, Al-2.0Zn-1.7Mg-0.2Cu and Al-1.9Zn-1.7Mg (at.%). The early RH reaction in these alloys accounts for up to 70% of the total hardening (peak hardness minus as-quenched hardness) and takes place during the first 60 seconds of ageing. We report preferred solute-solute interactions in the as-quenched materials. This quenched-in nanostructure acts as a template for subsequent solute clustering, the nature of which we have correlated with ageing.

scholarly journals A 2-DIMENSIONAL CELLULAR AUTOMATON FOR AGENTS MOVING FROM ORIGINS TO DESTINATIONS

2005 ◽  
Vol 16 (12) ◽  
pp. 1849-1860 ◽  
Author(s):  
NAJEM MOUSSA
Keyword(s):  
Cellular Automaton ◽  
Cluster Size ◽  
Bimodal Distribution ◽  
Minimal Distance ◽  
Time Step ◽  
Neighbor Site ◽  
Model Dynamics ◽  
Long Time ◽  
Freely Moving ◽  
Small Clusters

We develop a two-dimensional cellular automaton (CA) as a simple model for agents moving from origins to destinations. Each agent moves towards an empty neighbor site corresponding to the minimal distance to its destination. The stochasticity or noise (p) is introduced in the model dynamics, through the uncertainty in estimating the distance from the destination. The friction parameter "μ" is also introduced to control the probability that movement of all involved agents to the same site (conflict) is denied at each time step. This model displays two states; namely the freely moving and the jamming state. If μ is large and p is low, the system is in the jamming state even if the density is low. However, if μ is large and p is high, a freely moving state takes place whenever the density is low. The cluster size and the travel time distributions in the two states are studied in detail. We find that only very small clusters are present in the freely moving state, while the jamming state displays a bimodal distribution. At low densities, agents can take a very long time to reach their destinations if μ is large and p is low (jamming state); but long travel times are suppressed if p becomes large (freely moving state).

scholarly journals Uwarunkowania procesu pojednania w Kambodży

2020 ◽  
Vol 14 ◽  
pp. 267-280
Author(s):  
Radosław Zarzecki
Keyword(s):  
Early Stage ◽  
Khmer Rouge ◽  
State Level ◽  
Political Life ◽  
Historical Background ◽  
Difficult Situation ◽  
Main Challenge ◽  
Long Time ◽  
History Of ◽  
Culture Of Silence

Determinants of Reconciliation in Cambodia Forty years after Cambodian genocide the reconciliation is still in early stage. Despite such long time there was almost nothing done, especially in 20th century, to make that process happened. The article discusses the determinants, reasons and factors that had impact on reconciliation. Determinants can be divided into different categories. First of all the socio-historical background. Circumstances in which Khmer Rouge come to power, their revolutionary approach to economy, implemented reforms, use of children, displacements of people and categorization of citizens had great impact on post-1979 Cambodia. Another determinant is a political one. Policy of post-Khmer Rouge Cambodia rulers stunted the reconciliation. There reason of such actions are multidimensional but the most important one is provenance of People’s Republic of Kampuchea leaders. The most important figures in Cambodia politics are ex-Khmer Rouge soldiers, accused by some of taking a part in genocide. What’s even more confusing, the most powerful opposition party in 1980s were perpetrators themselves and their allies. Even after signing Paris Peace Accords in 1991 until early 2000s there was no will to punish Khmer Rouge officials responsible for genocide. The Cambodian culture of silence, the third determinant, only exacerbates a difficult situation. Cambodians rarely speak about atrocities and harsh past because of fear, shame or trauma. Even in school textbooks until 2009 there was almost nothing said about tragic events which happened between 1975 and 1979. History of Democratic Kampuchea still affects the Cambodian society. Despite sentencing few Khmer Rouge officials in 2010s, there’s still lot to be done also on state-level. Reconciliation and coming back to the state of balance is the main challenge for Cambodia in the nearest future, crucially important to social and political life of this nation.

scholarly journals Effect of Dissolution of η′ Precipitates on Mechanical Properties of A7075-T6 Alloy

2022 ◽  
Vol 60 (1) ◽  
pp. 83-93
Author(s):  
Young-We Kim ◽  
Yong-Hee Jo ◽  
Yun-Soo Lee ◽  
Hyoung-Wook Kim ◽  
Je-In Lee
Keyword(s):  
Mechanical Properties ◽  
Yield Strength ◽  
Solution Treatment ◽  
Aluminum Matrix ◽  
Natural Aging ◽  
Aging Treatment ◽  
Nucleation Site ◽  
Treatment Temperature ◽  
Solution Treatment Temperature ◽  
Bake Hardening

The effects of dissolution of the η′ phase by solution treatment on the mechanical properties of A7075-T6 alloy were investigated. Immediately after solution treatment of the T6 sheet at 450 oC or higher, elongation significantly increased and dissolution of the η′ phase occurred. η′ is the main hardening phase. After natural-aging, GPI, which is coherent with the aluminum matrix, was formed and strength increased. When bake hardening after natural-aging was performed, the yield strength slightly increased due to partial dissolution of the GPI and re-precipitation of the η′ phase. In contrast, after solution treatment at 400 oC, there was less elongation increase due to the precipitation of the coarse η phase at grain boundaries and low dissolution of the η′ phase. In addition, when bake hardening after natural-aging was performed, the yield strength decreased due to insufficient GPI, which is the nucleation site of the η′ phase. To promote reprecipitation of the η′ phase, the solution treatment temperature was set to a level that would increase solubility. As a result, the yield strength was significantly increased through re-precipitation of a large number of fine and uniform η′ phase. In addition, to increase the effect of dissolution, a pre-aging treatment was introduced and the bake hardenability can be improved after dissolution.

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