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  • Author: D. Dışpınar x
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E. Erzi, D. Dispinar and S. Yilmaz

Abstract

In this study T6 heat treated 6063 aluminum alloys were used as substrate material. In order to form a bond between the substrate and the main coating, all samples were coated with Ni-Cr-Al powders. 8 wt% Yttria Stabilized Zirconia powders (YSZ) were coated with plasma spray technique. Thickness of YSZ was 150 μm and bond coating was 36 m. XRD and SEM-EDS analyses were performed to characterize the coating layers. These YSZ coated and uncoated samples were subjected to wear testing under different spindle speed, loading and working distance. Wear test results were compared with the kinetic friction coefficients and weight loss values. Wear marks on YSZ coated and uncoated samples were investigated by SEM analysis. By coating with plasma spray technique, the wear resistance of Al alloys was increased without changing the friction coefficient. It was found that spindle speed had significant effect over the wear properties than the load applied. By YSZ coating, wear properties were increased 10 times.

Open access

M. Çolak and D. Dışpınar

Abstract

Grain refining and modification are common foundry practice for improving properties of cast Al-Si alloys. In general, these types of treatments provide better fluidity, decreased porosity, higher yield strength and ductility. However, in practice, there are still some discrepancies on the reproducibility of the results from grain refining and effect of the refiner’s additions. Several factors include the fading effect of grain refinement and modifiers, inhomogeneous dendritic structure and non-uniform eutectic modification. In this study, standard ALCAN test was used by considering Taguchi’s experimental design techniques to evaluate grain refinement and modification efficiency. The effects of five casting parameters on the grain size have been investigated for A357 casting alloy. The results showed that the addition of the grain refiner was the most effective factor on the grain size. It was found that holding time, casting temperature, alloy type and modification with Sr were less effective over grain refinement.

Open access

M. Uludağ, R. Çetin and D. Dışpınar

Abstract

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 250°C and the pouring was carried out at 740°C. 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.

Open access

M. Uludağ and D. Dişpinar

Abstract

It is well-known that the better the control of the liquid aluminium allows obtaining of better properties. One of the most important defects that is held responsible for lower properties has been the presence of porosity. Porosity has always been associated with the amount of dissolved hydrogen in the liquid. However, it was shown that hydrogen was not the major source but only a contributor the porosity. The most important defect that causes porosity is the presence of bifilms. These defects are surface entrained mainly due to turbulence and uncontrolled melt transfer. In this work, a cylindrical mould was designed (Ø30 x 300 mm) both from sand and die. Moulds were produced both from sand and die. Water cooled copper chill was placed at the bottom of the mould in order to generate a directional solidification. After the melt was prepared, prior to casting of the DC cast samples, reduced pressure test sample was taken to measure the melt quality (i.e. bifilm index). The cast parts were then sectioned into regions and longitudinal and transverse areas were investigated metallographically. Pore size, shape and distribution was measured by image analysis. The formation of porosity was evaluated by means of bifilm content, size and distribution in A356 alloy.

Open access

M. Uludağa, M. Uyaner, F. Yilmaz and D. Dişpinar

Abstract

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.

Open access

M. Uludağ, M. Kocabaş, D. Dışpınar, R. Çetin and N. Cansever

Abstract

In the present study, the corrosion behaviour of A356 (Al-7Si-0.3Mg) alloy in 3.5% NaCl solution has been evaluated using cyclic/potentiodynamic polarization tests. The alloy was provided in the unmodified form and it was then modified with AlTi5B1 for grain refinement and with AlSr15 for Si modifications. These modifications yield to better mechanical properties. Tensile tests were performed. In addition, bifilm index and SDAS values were calculated and microstructure of the samples was investigated. As a result of the corrosion test, the Ecorr values for all conditions were determined approximately equal, and the samples were pitted rapidly. The degassing of the melt decreased the bifilm index (i.e. higher melt quality) and thereby the corrosion resistance was increased. The lowest corrosion rate was founded at degassing and as-received condition (3.9x10-3 mm/year). However, additive elements do not show the effect which degassing process shows.

Open access

C. Yuksel, O. Tamer, E. Erzi, U. Aybarc, E. Cubuklusu, O. Topcuoglu, M. Cigdem and D. Dispinar

Abstract

A356 is one of the widely used aluminium casting alloy that has been used in both sand and die casting processes. Large amounts of scrap metal can be generated from the runner systems and feeders. In addition, chips are generated in the machined parts. The surface area with regard to weight of chips is so high that it makes these scraps difficult to melt. Although there are several techniques evolved to remedy this problem, yet the problem lies in the quality of the recycled raw material. Since recycling of these scrap is quite important due to the advantages like energy saving and cost reduction in the final product, in this work, the recycling efficiency and casting quality were investigated. Three types of charges were prepared for casting: %100 primary ingot, %100 scrap aluminium and fifty-fifty scrap aluminium and primary ingot mixture were used. Melt quality was determined by calculating bifilm index by using reduced pressure test. Tensile test samples were produced by casting both from sand and die moulds. Relationship between bifilm index and tensile strength were determined as an indication of correlation of melt quality. It was found that untreated chips decrease the casting quality significantly. Therefore, prior to charging the chips into the furnace for melting, a series of cleaning processes has to be used in order to achieve good quality products.