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

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

REDUCED PRESSURE TEST (RPT) FOR BIFILM ASSESSMENT

The assessment of the cleanness of liquid aluminum alloys has traditionally been viewed as difficult, but has been tackled by a number of techniques, all of which have been comparatively expensive and complicated. In the past the presence of entrained defects known as bifilms in metals has not been realised because they are often only a few molecules thick, and so remain invisible, or at best, difficult to detect. The reduced pressure test (RPT) is sensitive to the size and number of entrained oxides which appear to be the major defects affecting metal quality in terms of workability, mechanical properties and corrosion. In addition, the test is a confirmation of the fact that such oxides are double, and thus conveniently called `bifilms'. The RPT is a simple, low cost, but fundamentally appropriate technique for the assessment of (a) the number and (b) the size of bifilms in a melt. This paper outlines an initial draft procedure. Future users will be welcome to suggest improvements

Taguchi Approach for Optimization of Parameters that Effect Grain Size of Cast A357 Alloy

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

STUDYING ON THE EFFECTS OF QUENCHING RATE ON RESIDUAL STRESS IN Al-5Mg and Al-Mg-Cu ALLOYS

In aluminium alloys, Cu and Mg are added in order to increase the strength. Obtained alloys are subjected to solution treated and precipitation hardening (T6) processing. Phases are formed with simultaneous diffusions of Cu and Mg in these alloys. The purpose of this study is the modelling of elements, which are in Al-Cu, Al-Mg and Al-Cu-Mg alloys, solution treatment times into alloys both one by one and in an interrelated way and their microstructural changings. Alloys are produced by pouring to both sand and metal mould. Then, these samples are subjected to solution treated and precipitation hardening processing in different temperatures and for different periods of time. Solution treated speeds of obtained samples are examined with microstructure and image analyses through metallographic examination and a model is designed. Microhardness analyses are also made. On the other hand, residual stress of alloys are examined with hardness, DSC and microstructure analyses

The Effect of Desulfovibrio sp Biofilms on Corrosion Behavior of Copper in Sulfide-Containing Solutions

This study aims to detect the effect of Desulfovibrio sp. on copper in terms of biofilm formation and corrosion in 722 h. In that way, appropriate strategies to inhibit microbiological corrosion in copper systems with Desulfovibrio sp. can be evaluated. For this purpose, experiments were performed in 1 L glass model system containing 28 copper coupons and pure culture of the sulfate-reducing bacteria (SRB) strain Desulfovibrio sp. in Postgate's medium C. Also, a control system with copper coupons but without Desulfovibrio sp. containing sterile Postgate's medium was studied concurrently with the test system. The test coupons were collected from systems at certain time intervals, namely 24, 168, 360, and 720 h. The samples were then subjected to several characterization analyses such as measurement of Desulfovibrio sp. numbers, corrosion resistance, EPS extraction, carbohydrate analysis, SEM, and EDS. During the experiments, the maximum Desulfovibrio sp. count in biofilm samples was found at 360 h. Carbohydrate and copper concentrations in biofilm were increased over time. EDS analysis revealed Cu, S, C, O, and Cl peaks on the surface of the samples. For the control coupons, only Cu peaks were observed. The results obtained from this study showed that copper was corroded by Desulfovibrio sp. in the model system under laboratory conditions

Freezing Range, Melt Quality, and Hot Tearing in Al-Si Alloys

In this study, three different aluminum-silicon alloys (A356, A413, and A380) that have different solidification morphology and solidification ranges were examined with an aim to evaluate the hot tearing susceptibility. T-shape mold and Constrained Rod Casting (CRC) mold were used for the characterization. Reduced Pressure Test (RPT) was used to quantify the casting quality by measuring bifilm index. It was found that bifilm index and solidification range have an important role on the hot tearing formation. As it is known, bifilms can cause porosity and in this case, it was shown that porosity formed by bifilms decreased hot tearing tendency. As the freezing range of alloy increases, bifilms find the time to unravel that reduces hot tearing. However, for eutectic alloy (A413), due to zero freezing range, regardless of bifilm content, hot tearing was never observed. A380.1 alloy had the highest tendency for hot tearing due to having the highest freezing range among the alloys investigated in this work

Melt Cleanliness Comparison of Chlorine Fluxing and Ar Degassing of Secondary Al-4Cu

The treatment of liquid aluminum prior to casting typically consists of purging gas and/or fluxes through the melt. By the use of several chemicals during these operations, several environmental problems can occur. Therefore, in this study, the melt cleanliness of Al-4Cu secondary alloy was investigated by comparing the use of argon degassing with or without chlorine fluxing. Reduced pressure test was used to assess the melt quality. Highest quality melt was obtained by Ar degassing with preheated graphite lance without the need to use any chemicals

CORRELATION BETWEEN MELT QUALITY AND FLUIDITY OF A356

Aluminium and its alloys are prefer choice of automotive parts due to their low density and high strength ratios. These critical applications requires high quality castings to be produced. Melt quality can be measured by bifilm index using reduced pressure test. This index is a numerical indication of bifilm quantity of the melt. It has been shown that these bifilms affect many of the properties significantly. One of the limiting factor of casting methods is the fluidity of the liquid metal. The aim of the study is to investigate the effect of bifilms (i.e. melt quality) over the fluidity of A356 by using spiral test mould. Different mould temperatures were studied and it was found that as the bifilm index was increased, the scatter of the test results was increased

CORRELATION BETWEEN BIFILM INDEX AND TOUGHNESS OF ALUMINUM ALLOYS

The measurement of melt quality of aluminum alloys have been a complex phenomenon. There exists various methods but the general experience show that they were slow, complicated or expensive for use on the foundry floor. In addition, these methods were not quantifiable. For the first time, bifilm index was proposed by the authors which give a numerical indication of the melt quality in millimeters as the total oxide length. Numerous studies were carried out to correlate this index with the mechanical properties. In this work, toughness measurements were made by using MatLab software. Alloy studied was 356 which were cast under various conditions (degassed and upgassed for 0.1, 0.2 and 0.4 cm(3)/100g Al) and the results were correlated with bifilm index

Influence of Different Cross Sections on Fluidity Characteristics of A356

Fluidity of cast metals are typically measured by the length of metal that is stopped by the solidification where the filling is carried out at a constant cross sectional mold cavity. In this work, a sand mold geometry with different section thicknesses were used to measure the fluidity characteristics of A356 alloy at various casting temperatures (700, 725, 750 A degrees C) with and without modifications. It was found that Ti modification had no significant effect on fluidity. On the other hand, the highest fluidity was achieved by Sr modification even at low pouring temperatures. The results were compared with simulation software (SolidCast), and critical fraction of liquid (CFL) was determined