• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.556-564
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• 1996

Variation of shape and size of solid particles and solute redistribution in Mg-9wt.%Al, AI-4.5wt.% Cu, and AI-7wt.%Si alloys were investigated when they were heated to semi-solid temperatures and held without stirring. In the case of Mg-9wt.% Al and Al-4.5wt.%Cu alloys, the polygonal shaped solid particles were agglomerated with non-uniform distribution, and there were no disappearance of the solid/solid boundary until the end of melting. But in the case of an Al-7wt.%Si alloys, two or three spherical shaped particles were coalesced or separated individually, and the coalesced particles had no solid/solid interface on the contrary to the prevous case. The maximum size of solid particles during isothermal heating at high temperature was smaller than that at lower temperature, but the time required to reach the maximum size at high temperature was shorter than that at lower temperature. The concentrations of main solute atom whose distribution coefficient is lower than 1, decreased in the primary solid particles as the liquid fraction increased, and the gradient of solute concentration was steeper in Mg-9wt.%Al alloy and Al-4.5wt.%Cu alloy than that of Al-7wt.%Si alloy.

• Korean Journal of Materials Research
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• v.22 no.2
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• pp.82-85
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• 2012

The effect of the alloy systems Al-Mg alloy and Al-Si alloy in this study on the characteristics of die-casting were investigated using solidification simulation software (MAGMAsoft). Generally, it is well known that the casting characteristics of Al-Mg based alloys, such as the fluidity, feedability and die soldering behaviors, are inferior to those of Al-Si based alloys. However, the simulation results of this study showed that the filling pattern behaviors of both the Al-Mg and Al-Si alloys were found to be very similar, whereas the Al-Mg alloy had higher residual stress and greater distortion as generated due to solidification with a larger amount of volumetric shrinkage compared to the Al-Si alloy. The Al-Mg alloy exhibited very high relative numbers of stress-concentrated regions, especially near the rib areas. Owing to the residual stress and distortion, defects were evident in the Al-Mg alloy in the areas predicted by the simulation. However, there were no visible defects observed in the Al-Si alloy. This suggests that an adequate die temperature and casting process optimization are necessary to control and minimize defects when die casting the Al-Mg alloy. A Tatur test was conducted to observe the shrinkage characteristics of the aluminum alloys. The result showed that hot tearing or hot cracking occurred during the solidification of the Al-Mg alloy due to the large amount of shrinkage.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.6
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• pp.295-302
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• 2022

The present study aims to investigate the effect of Al content on microstructure and hardness of discontinuous precipitates (DPs) formed by continuous cooling (CC) in Mg-8%Al and Mg-9.5%Al alloys. The DPs had a wide range of (α+β) interlamellar spacings, which may well be attributed to the different transformation temperatures during CC. The higher Al content gave rise to the higher level of interlamellar spacings of the DPs, and thicker and larger amount of β phase layer in the DPs. It is noticeable that the Mg-9.5%Al alloy exhibited higher hardness of the DPs than the Mg-8%Al alloy, but the ratio of increase in hardness of the DPs compared to that of the as-cast state was similar regardless of the Al content. The reason was discussed based on the differences in microstructures of the DPs for the Mg-8%Al and Mg-9.5%Al alloys.

• Transactions of Materials Processing
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• v.21 no.5
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• pp.324-329
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• 2012

Mg-(9-x)Sn-xAl-1Zn (x=1, 2, 3 and 4 wt.%) alloys were subjected to indirect extrusion, and the microstructure and mechanical properties of the as-extruded Mg-Sn-Al-Zn (TAZ) alloys were investigated. The TAZ 811 alloy exhibited a finer grain structure than the TAZ 541 alloy due to a larger number of Mg2Sn particles, which pinned the grain boundaries and prevented growth of recrystallized grains. The TAZ alloys showed an unusual yield asymmetry behavior. The tension-compression yield asymmetry increased with decreasing average grain size. The TAZ 811 alloy with a small grain size exhibited a larger yield asymmetry than that of the TAZ 541 alloy having a relatively large grain size, which is mainly attributed to the low Al content and large number of second phase particles in the TAZ 811 alloy.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.4
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• pp.175-180
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• 2012

Role of Ca in grain growth behavior has been investigated in hot-rolled Al-3%Mg and Al-3%Mg-0.5%Ca wrought alloys. When annealed for 1 hr from 723 to 823 K, grain size of the Al-3%Mg alloy increased rapidly above 723 K, whereas grains were relatively stable up to 773 K for the Ca-containing alloy. Grain homogeneity of the Ca-containing alloy was better than that of the Ca-free alloy both in hot-rolled and annealed states. Calculated activation energies for grain growth were 77.6 and 85.9 kJ/mole in the range of 723 to 823 K for the alloys with 0 and 0.5%Ca, respectively. Taking SEM images and EDS results into account, enhanced thermal stability in response to Ca addition would be associated with Al4Ca compounds located along the grain boundaries, which eventually play a role in restricting grain growth at elevated temperatures.

• Journal of Powder Materials
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• v.30 no.6
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• pp.470-477
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• 2023

The effects of annealing on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Si alloys fabricated by high-energy ball milling (HEBM) and spark plasma sintering (SPS) were investigated. The HEBM-free sintered alloy primarily contained Mg₂Si, Q-AlCuMgSi, and Si phases. Meanwhile, the HEBM-sintered alloy contains Mg-free Si and θ-Al₂Cu phases due to the formation of MgO, which causes Mg depletion in the Al matrix. Annealing without and with HEBM at 500℃ causes partial dissolution and coarsening of the Q-AlCuMgSi and Mg₂Si phases in the alloy and dissolution of the θ-Al₂Cu phase in the alloy, respectively. In both alloys, a thermally stable α-AlFeSi phase was formed after long-term heat treatment. The grain size of the sintered alloys with and without HEBM increased from 0.5 to 1.0 ㎛ and from 2.9 to 6.3 ㎛, respectively. The hardness of the sintered alloy increases after annealing for 1 h but decreases significantly after 24 h of annealing. Extending the annealing time to 168 h improved the hardness of the alloy without HEBM but had little effect on the alloy with HEBM. The relationship between the microstructural factors and the hardness of the sintered and annealed alloys is discussed.

• Journal of Welding and Joining
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• v.22 no.5
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• pp.53-57
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• 2004

Friction stir weldability of AZ31B-H24, AZ61A-F and AZ91C-F Mg alloys were studied using microstructural observation and mechanical tests. The microstructure of stir zone(SZ) was coarse in AZ31B-H24 alloy whereas it was very fine both in AZ61A-F and AZ91C-F alloys. The hardness of SZ was remarkably increased by very fine recrystallized grains both in AZ61A-F and AZ91C-F alloys. On the other hand, the hardness of SZ was decreased in AZ31B-H24 due to the coarse microstructure. In SZ, AZ91C-F alloy showed very high hardness values because of dispersion hardening of $Mg_{17}$Al$_{12}$($\beta$ phase) and Al solid solution hardening. Because of more $Mg_{ 17}Al_{12}($\beta$ phase)$ intermetallic compounds, Mg alloy with high Al content showed poor mechanical properties.s.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.2
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• pp.81-92
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• 1997

The effect of alloying elements, precipitate size, its distribution, and dislocation substructure resulted from warm rolling or cold rolling in the superplastic Al-Mg alloy system was investigated. One of the major requirements for fine structure superplasticity is that the grain size should be very small. Fine grain structure is controlled by the dislocation substructure and the dynamic recrystallization during hot or warm working. The recovery of Al-Mg base alloys was constrained resulting in relatively high dislocation density when the alloys were warm rolled. In particular, Al-Mg-Zr alloy exhibited the smallest sub-grain size among Al-Mg alloys containing Mn, Cu, Zr as a third element. The Al-Mg-Mn alloy cold rolled 80% after hot rolling showed the maximun strain rate sensitivity exponent, m, of 0.75 under strain rate of $7.1{\times}10^{-4}/s$ at $500^{\circ}C$. The elongation of the alloys was limited in spite of high m values due to large dispersoids containing appreciable amount of Fe impurities.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.1
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• pp.10-16
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• 1998

The softening behavior of squeeze cast Mg-Li-Al and Mg-Li-Al-Zr alloys have been investigated. The highest hardness values of Mg-Li-Al and Mg-Li-Al-Zr alloys were obtained after solution treatment at $400^{\circ}C$ for 1 hour. The hardness value, however, decreased as the aging temperature and time increased. Microstructural and calorometric analyses showed that quenched-microstructure changed from primary (${\alpha}$ and ${\beta}$)+secondary ${\alpha}$ to primary(${\alpha}$ and ${\beta}$)+secondary ${\alpha}+{\theta}$ after aging. The softening during aging was due to the coarsening of ${\theta}$ precipitates.

• Journal of Korea Foundry Society
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• v.17 no.4
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• pp.356-364
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• 1997

In order to study effects of Cu and Be on the microstructure and tensile properties of rapidly solidified Al-Mg alloys, Al-Mg-Cu-Be alloys have been rapidly solidified by inert gas atomization process. Microstructure of rapidly solidified Al-Mg-Cu-Be powders exhibited refinement and good dispersion of Be particles as increasing of solidification rate. Solidification rate of atomized powders was estimated to be about $5{\times}10^{3{\circ}}C/s$. Inert gas atomized Al-Mg-Cu-Be powders were hot-processed by vacuum hot pressing at $450^{\circ}C$ under 100 MPa and hot extruded with reduction ratio in area of 25: 1 at $450^{\circ}C$. The extruded Al-Mg-Cu-Be powders consisted of recrystallized fine Al grains and homogeneously dispersed fine Be particles, and exhibited improved tensile properties with increase in Cu content. $Al_2CuMg$ compounds precipitated in grain and grain boundaries of Al-Mg-Cu-Be alloys with aging heat treatment after solution treatment. Hardness and tensile properties were improved by increasing Cu content and Be addition. Compared with extruded Al-Mg-Cu powders, the extruded Al-Mg-Cu-Be powders exhibited finer recrystallized grains and improved tensile properties by dispersion hardening of Be and subgrain boundaries pinned by fine Be particles. After aging treatment, hardness and tensile properties were improved due to restricted precipitation by increasing of dislocation density around Be particles in matrix.