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1

Influence of Defects on Deformation Behavior of High-Pressure Die-Casting Magnesium Alloys

Braszczyńska-Malik Katarzyna

Archives of Foundry Engineering

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2023

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Vol. 23, iss. 2

10--14

EN

The results of investigations of defects in AME-series magnesium alloys produced by the high-pressure die-casting method are presented. The analyzed magnesium alloys contain about 5 wt% aluminum and 1-5 wt% rare earth elements introduced in the form of mischmetal. The casts were fabricated using a regular type cold-chamber high-pressure die-casting machine with a 3.2 MN locking force. The same surfaces of the casts were analyzed before and after the three-point bending test in order to determine the influence of the gas and shrinkage porosity on the deformation behavior of the alloys. The obtained results revealed that the most dangerous for the cast elements is the shrinkage porosity, especially stretched in the direction perpendicular to the that of the tensile stress action. Additionally, the influence (Mg) solid solution and its interaction on the cracking process was described [alpha]  of deformation twins arise in the dendrites of the primary.

2

Shrinkage Porosity Criterion and Its Application to A 5.5 Ton Steel Ingot

Zhang C., Bao Y., Wang M., Zhang L.

Archives of Foundry Engineering

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2016

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Vol. 16, iss. 2

27--32

EN

In order to predict the distribution of shrinkage porosity in steel ingot efficiently and accurately, a criterion R√L and a method to obtain its threshold value were proposed. The criterion R√L was derived based on the solidification characteristics of steel ingot and pressure gradient in the mushy zone, in which the physical properties, the thermal parameters, the structure of the mushy zone and the secondary dendrite arm spacing were all taken into consideration. The threshold value of the criterion R√L was obtained with combination of numerical simulation of ingot solidification and total solidification shrinkage rate. Prediction of the shrinkage porosity in a 5.5 ton ingot of 2Cr13 steel with criterion R√L>0.21 m･℃1/2･s-3/2 agreed well with the results of experimental sectioning. Based on this criterion, optimization of the ingot was carried out by decreasing the height-to-diameter ratio and increasing the taper, which successfully eliminated the centreline porosity and further proved the applicability of this criterion.

3

Prediction of Shrinkage Porosity in Femoral Stem of Titanium Investment Casting

Sutiyoko, Suyitno, Mahardika M., Syamsudin A.

Archives of Foundry Engineering

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2016

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Vol. 16, iss. 4

157--162

EN

Design of gating system is an important factor in obtaining defect-free casting. One of the casting defects is a porosity caused by internal shrinkage in solidification process. Prediction of the internal shrinkage porosity in the femoral stem of commercially pure titanium (CP-Ti) is investigated based on the gating system design. The objective of this research is to get the best gating system between three gating system designs. Three gating system designs of the femoral stem were simulated in an investment casting method. The internal shrinkage porosity occurs on the largest part and near the ingate of the femoral stem. The gating system design that has ingates cross section area: 78.5; 157; and 128.5 mm2 has the least of the internal shrinkage porosity. This design has the most uniform solidification in the entire of the femoral stem. An experiment is conducted to validate the simulation data. The results of internal shrinkage porosity in the three gating system designs in the simulation were compared with the experiment. Based on the comparison, the trend of internal shrinkage porosity at the three gating system designs in the simulation agrees with the experiment. The results of this study will aid in the elimination of casting defect.

4

The Effect of Shell Thickness, Insulation and Casting Temperature on Defects Formation During Investment Casting of Ni-base Turbine Blades

Raza M., Irwin M., Fagerström B.

Archives of Foundry Engineering

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2015

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Vol. 15, iss. 4

115--123

EN

Turbine blades have complex geometries with free form surface. Blades have different thickness at the trailing and leading edges as well as sharp bends at the chord-tip shroud junction and sharp fins at the tip shroud. In investment casting of blades, shrinkage at the tip-shroud and cord junction is a common casting problem. Because of high temperature applications, grain structure is also critical in these castings in order to avoid creep. The aim of this work is to evaluate the effect of different process parameters, such as, shell thickness, insulation and casting temperature on shrinkage porosity and grain size. The test geometry used in this study was a thin-walled air-foil structure which is representative of a typical hot-gas-path rotating turbine component. It was observed that, in thin sections, increased shell thickness helps to increase the feeding distance and thus avoid interdendritic shrinkage. It was also observed that grain size is not significantly affected by shell thickness in thin sections. Slower cooling rate due to the added insulation and steeper thermal gradient at metal mold interface induced by the thicker shell not only helps to avoid shrinkage porosity but also increases fill-ability in thinner sections.

5

Contribution to the Identification of Porosity Type in AlSiCu High-Pressure-Die-Castings by Experimental and Virtual Way

Ignaszak Z., Hajkowski J.

Archives of Foundry Engineering

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2015

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Vol. 15, iss. 1

143--151

EN

The paper concerns the problem of discontinuity in high pressure die castings (HPDC). The compactness of their structure is not perfect, as it is sometimes believed. The discontinuities present in these castings are the porosity as follow: shrinkage and gas (hydrogen and gas-air occlusions) origin. The mixed gas and shrinkage nature of porosity makes it difficult to identify and indicate the dominant source. The selected parameters of metallurgical quality of AlSi9Cu3 alloy before and after refining and the gravity castings samples (as DI - density index method), were tested and evaluated. This alloy was served to cast the test casting by HPDC method. The penetrating testing (PT) and metallographic study of both kinds of castings were realized. The application of the NF&S simulation system allowed virtually to indicate the porosity zones at risk of a particular type in gravity and high-pressure-die-castings. The comparing of these results with the experiment allowed to conclude about NF&S models validation. The validity of hypotheses concerning the mechanisms of formation and development of porosity in HPDC casting were also analyzed.

6

The role of metallurgical defects and microstructure on failure formation in roll necks of cast iron rolls

Krawczyk J., Pacyna J.

Metallurgy and Foundry Engineering

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2007

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Vol. 33, no. 2

89-96

EN

This work presents the examples of structural reasons for failure of the necks of cast iron rolls. The most common reason for damage of metallurgical roll necks is a presence of shrinkage porosity in their volume. Moreover, a high fraction of ledeburitic cementite can lead to the formation of a continuous net of eutectic carbides, which facilitate cracking. Even very thin net of secondary carbides, formed on the boundaries of former grain of austenite, can significantly facilitate propagation of the crack. Continuous net of ledeburitic cementite, in the case of its precipitation in a form of bands and existence of hardened areas in the alloy matrix can lead to roll neck fracture relatively easy. The use of flake graphite cast iron for metallurgical rolls increases a risk of the fracture of roll neck.

PL

W niniejszej pracy przedstawiono przykłady strukturalnych przyczyn uszkodzeń czopów w żeliwnych walcach hutniczych. Najczęstszą przyczyną uszkodzeń czopów walców hutniczych jest zaleganie w nich obszarów rzadzizn. Ponadto duży udział cementytu ledeburytycznego może prowadzić do powstania ciągłej siatki węglików eutektycznych, która tworzy drogę łatwego pękania. Nawet bardzo cienka siatka węglików drugorzędowych utworzona na granicach pierwotnego ziarna austenitu może w znaczący sposób ułatwiać rozwój pęknięcia. Ciągła siatka cementytu ledeburytycznego, w przypadku jego wydzielania w postaci pasmowej oraz występowanie w osnowie obszarów podhartowanych, może doprowadzić do łatwego złamania czopa walca. Zastosowanie na walce hutnicze żeliwa z grafitem płatkowym zwiększa niebezpieczeństwo złamania czopa.