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The Effect of Bifilm and Sr Modification on the Mechanical Properties of AlSi12Fe Alloy

Uludağ M., Gurtaran M., Dispinar D.

Archives of Foundry Engineering

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2020

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Vol. 20, iss. 3

99--104

EN

The microstructure of Al-Si alloy has coarse silicon and this structure is known dangerous for mechanical properties due to its crack effect. Sr addition is preferred to modify the coarse silica during solidification. Additionally, bifilms (oxide structure) are known as a more dangerous defect which is frequently seen in light alloys. It is aimed at that negative effect of bifilms on the properties of the alloys tried to be removed by the degassing process and to regulate the microstructure of the alloy. In this study, the effect of degassing and Sr modification on the mechanical properties of AlSi12Fe alloy was investigated, extensively. Four different parameters (as-received, as-received + degassing, Sr addition, Sr addition + degassing) were studied under the same conditions environmentally. The microstructural analyses and mechanical tests were done on cast parts. All data obtained from the experimental study were analyzed statistically by using statistical analysis software. It was concluded from the results that Sr addition is very dangerous for AlSi12Fe alloy. It can be suggested that to reach high mechanical properties and low casting defects, the degassing process must be applied to all castings whereas Sr addition should not be preferred.

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Observation of Hot Tearing in Sr-B Modified A356 Alloy

Uludağ M., Çetin R., Dışpınar D.

Archives of Foundry Engineering

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2017

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Vol. 17, iss. 4

165--168

EN

In this work, T-shaped mould design was used to generate hot spot and the effect of Sr and B on the hot tearing susceptibility of A356 was investigated. The die temperature was kept at 250ºC and the pouring was carried out at 740ºC. The amonut of Sr and B additions were 30 and 10 ppm, respectively. One of the most important defects that may exist in cast aluminium is the presence of bifilms. Bifilms can form by the surface turbulence of liquid metal. During such an action, two unbonded surfaces of oxides fold over each other which act as a crack. Therefore, this defect cause many problems in the cast part. In this work, it was found that bifilms have significant effect over the hot tearing of A356 alloy. When the alloy solidifies directionally, the structure consists of elongated dendritic structure. In the absence of equiaxed dendrites, the growing tips of the dendrites pushed the bifilms to open up and unravel. Thus, leading to enlarged surface of oxide to become more harmful. In this case, it was found that these bifilms initiate hot tearing.

3

Mechanical Properties and Melt Quality Relationship of Sr-modified Al-12Si Alloy

Uludağ M., Uyaner M., Yilmaz F., Dişpinar D.

Archives of Foundry Engineering

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2015

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Vol. 15, iss. 4

134--140

EN

The formation of oxide film on the surface of aluminium melts, i.e. bifilms, are known to be detrimental when they are incorporated into the cast part. These defects causes premature fractures under stress, or aid porosity formation. In this work, Al-12 Si alloy was used to cast a step mould under two conditions: as-received and degassed. In addition, 10 ppi filters were used in the mould in order to prevent bifilm intrusion into the cast part. Reduced pressure test samples were collected for bifilm index measurements. Samples were machined into standard bars for tensile testing. It was found that there was a good agreement with the bifilm index and mechanical properties.