A new methodology for measurement of semi-solid constitutive behavior and its application to examination of as-cast porosity and hot tearing in aluminum alloys

Question

1. What is the effect of pre-existing porosity on the surface of a two?

2. What contributions have the authors mentioned in the paper "A new methodology for measurement of semi-solid constitutive behavior and its application to examination of as-cast porosity and hot tearing in aluminum alloys" ?

3. What is the effect of the as-cast material on ductility?

4. What is the effect of high casting rates on the surface of a cylindrical ingot?

Accepted Answer

Without pre-existing porosity, more strain must be applied to increase the dislocation / vacancy concentration and coalescence, and thus to create voids in a two-phase material composed of liquid and a highly compliant solid.

Accepted Answer

The effect of porosity on hot tearing was investigated using a novel semi-solid tensile deformation methodology combined with x-ray micro-tomography.. Further, it was shown that failure in this material is localized to the fracture surface with very little internal damage occurring in other areas.

Accepted Answer

Assuming that the grains are completely surrounded by liquid films, the pre-existing voids found in the as-cast material will act as stress risers enabling increase accumulation of damage and failure along the grain boundaries.

Accepted Answer

High casting rates lengthen the mushy zone, increase the solidification time, and therefore create a coarse grain structure, insufficient feeding to compensate the solidification shrinkage and the likelihood of increased porosity.

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After a 30 s hold at the test temperature for thermal stability, the cross-head is displaced at a rate of 50 m s-1, in increments of 25 m.

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While the casting surface is not normally prone to porosity, the hot casting conditions increase the surface solidification time and thus increase porosity.

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In the case of DC cast cylindrical billets, hot tearing occurs in the central part of the casting, when high casting rates are used.

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5. The application of the HIP process to the as-cast material has greatly reduced theamount of internal damage accumulated during semi-solid deformation, indicating that pre-existing as-cast porosity plays an important role in the formation of hot tears.

Accepted Answer

One feature of the Gleeble apparatus is that during specimen heat-up, an asymmetric parabolic temperature profile develops along the specimen length.

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Due to the parabolic temperature distribution and the difference in cross-sectional area, TC#2 remains at a significantly lower temperature during testing as compared to TC#1, and thus does not experience localized surface melting.

Accepted Answer

As proposed by Phillion et al., [43] the presence of free surface in the liquid in the form of as-cast porosity acts as a stress riser and allows strain to be accommodated by growth of this pre-existing void through the liquid along the grain boundary.

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in both cases, greater control over the as-cast porosity would lead to a reduction in hot tearing by reducing nucleation sites and thus increasing the amount of deformation required for hot tear propagation.

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due to the misalignment of the laser dilatometer as compared to strain localization, and also the accumulation of internal damage during deformation [40], it is still not possible to determine the true stress – true strain curve of the semi-solid material.

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These tensile tests have shown that semi-solid strength is strongly dependent on the fraction solid, microstructure size, morphology, and especially alloy chemistry [28, 36, 37].

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At 560°C, Fig. 7(d), the fracture surface appears to have been largely covered by liquid during deformation, leading to a complete loss in ductility.

Accepted Answer

Previous researchers have adopted two basic techniques for investigating semi-solid tensile constitutive behavior: partial remelting of the solid sample (e.g. [25]), and in situ solidification of the liquid melt (e.g. [33]).

A new methodology for measurement of semi-solid constitutive behavior and its application to examination of as-cast porosity and hot tearing in aluminum alloys

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Most frequently asked questions

1. What is the effect of pre-existing porosity on the surface of a two?

2. What contributions have the authors mentioned in the paper "A new methodology for measurement of semi-solid constitutive behavior and its application to examination of as-cast porosity and hot tearing in aluminum alloys" ?

3. What is the effect of the as-cast material on ductility?

4. What is the effect of high casting rates on the surface of a cylindrical ingot?

5. How long does the cross-head hold at the test temperature?

6. What is the effect of hot casting on the surface of aluminum alloys?

7. What is the effect of hot tearing on the surface of a DC cast cylindrical ingot?

8. What is the reason for the reduction of the internal damage accumulated during the as-cast process?

9. What is the asymmetric parabolic temperature profile of the Gleeble apparatus?

10. Why is TC#2 at a lower temperature during testing?

11. What is the effect of as-cast porosity on tearing?

12. What is the effect of reducing the as-cast porosity on hot tearing?

13. Why is it not possible to determine the true stress curve of the semi-solid material?

14. What are the main factors that influence the strength of semi-solid materials?

15. At what temperature did the fracture surface show a loss of ductility?

16. What are the two basic techniques for investigating semi-solid tensile behavior?

Figures

Citations

Tensile properties of as-deformed 2A50 aluminum alloy in semi-solid state

Inhomogeneity of density and mechanical properties of A357 aluminum alloy backward extruded in semi-solid state

X-ray tomography studies on porosity and particle size distribution in cast in-situ Al-Cu-TiB2 semi-solid forged composites

Effect of Ti on hot cracking and mechanical performance in the gas tungsten arc welds of copper thick plates

Interplay among Coating Thickness, Strip Size, and Thermal and Solidification Characteristics in A356 Lost Foam Casting Alloy

References

Behavior of metal alloys in the semisolid state

Mechanical properties in the semi-solid state and hot tearing of aluminium alloys

Modeling microporosity in aluminum–silicon alloys: a review

Hydrogen porosity in directional solidified aluminium-copper alloys:in situ observation

A technique for characterizing microsegregation in multicomponent alloys and its application to single-crystal superalloy castings

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