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Analysis of the Causes of Cracks in a Thick-Walled Bush Made of Die-Cast Aluminum Bronze

Pisarek B. P., Kołakowski D., Pacyniak T.

Archives of Foundry Engineering

2016

Vol. 16, iss. 4

119--124

For the die casting conditions of aluminium bronzes assumed based on the literature data, a thick-walled bush was cast, made of complex aluminium bronze (Cu-Al-Fe-Ni-Cr). After the cast was removed from the mould, cracks were observed inside it. In order to identify the stage in the technological production process at which, potentially, the formation of stresses damaging the continuity of the microstructure created in the cast was possible (hot cracking and/or cold cracking), a computer simulation was performed. The article presents the results of the computer simulation of the process of casting the material into the gravity die as well as solidifying and cooling of the cast in the shape of a thick-walled bush. The simulation was performed with the use of the MAGMA5 program and by application of the CuAl10Ni5,5Fe4,5 alloy from the MAGMA5 program database. The results were compared with the location of the defects identified in the actual cast. As a result of the simulation of the die-casting process of this bush, potential regions were identified where significant principal stresses accumulate, which can cause local hot and cold cracking. Until now, no research has been made of die-cast aluminium bronzes with a Cr addition. Correlating the results of the computer simulation validated by the analysis of the actual cast made it possible to clearly determine the critical regions in the cast exposed to cracking and point to the causes of its occurrence. Proposals of changes in the bush die casting process were elaborated, in order to avoid hot tearing and cold cracking. The article discusses the results of preliminary tests being a prologue to the optimization of the die-casting process parameters of complex aluminium bronze thick-walled bushs.

Prediction and validation of hot tearing in permanent mold steel casting using a viscoplastic damage model

Hadzic S., Schmidtne Kelity E., Sommitsch K.

Computer Methods in Materials Science

2013

Vol. 13, No. 1

36--42

Hot tears are unacceptable defects, which can be found in final steel casting products. It is believed that a hot tear forms at the mushy zone with a high fraction of solid due to an applied tensile strain. In this work the simulation of the solidification and deformation processes are carried out using commercial software combined with a user-defined constitutive model. The shrinkage porosity information is coupled to the constitutive deformation model in the solid state to calculate the materials damage, where a viscoplastic model can predict the hot tear formation in permanent mold steel alloy casting. A good correlation between experimental findings and predicted damage is observed.

Pękania są uszkodzeniami dyskwalifikującymi wyrób, mogącymi występować w produktach końcowych odlewania stali. Uważa się, że pękanie powstaje z powodu powstających naprężeń rozciągających w strefie pół-ciekłej przy wysokim tarciu ciała stałego. W niniejszej pracy symulacja krzepnięcia i proces deformacji przeprowadzone zostały przy zastosowaniu przemysłowego oprogramowania w połączeniu z określonym przez użytkownika modelem konstytutywnym. Informacja o powstałej w wyniku krzepnięcia rzadziźnie jest włączona do modelu konstytutywnego odkształceń w stanie stałym, co pozwala obliczyć uszkodzenie materiału. W tym przypadku model lepkoplastyczny może przewidzieć tworzenie się pęknięcia przy odlewaniu stopów stali do formy. Zaobserwowano dobrą korelację między wynikami doświadczalnymi i uszkodzeniami przewidywanymi przez model.