Papers by Author: Jerry Sokolowski

Abstract: This paper presents the prediction results of the temperature change during the solidification process of the cylinder head made of the AC2A aluminum alloy. Prediction results have been obtained by using the FDM solidification analysis based on two different solidification models were investigated. Here, the solidification model means functional relationship between the Temperature and the Fraction Solid. The first model is a simple Linear function and the second model is estimated from DSC measurement. The comparison between the simulated and measured temperatures of the aluminum cylinder head revealed that the selection of solidification models significantly reflects the prediction results. The DSC model gives higher prediction accuracy of the temperature change than the Linear model. The solidification models estimated by using Thermo- Calc and UMSA [3] were also investigated.

Abstract: Traditional gravity pour down-sprue methods of filling moulds in the making of aluminum castings inherently lead to oxide and air bubble entrainment. The reason for this is found in the high velocities the metal flow experiences during the filling of a mould. The Nemak Windsor Aluminum Plant (WAP) produces cylinder blocks using the low-pressure Cosworth process, which includes low velocity up-hill filling of the sand mould package. This doctrine is followed in all except one part of the process: the runner system. The nature of the resulting defect is generally known as Head Deck Porosity. Runners were cast full in open production runners at three different velocities with the resulting quickly chilled castings analyzed using X-ray radioscopy, and Scanning Electron Microscopy. Results reveal that the subject bubble porosity is indeed the result of air entrained during initial transient flow within the production runner system whose velocity is higher than the critical value of 0.5ms-1. This theoretical value is corroborated by experimental results. In addition, a new "sessile" runner of optimized shape, filled at a velocity slower than the critical value, is proposed and analyzed using Magmasoft mould fill modelling software. The design can potentially replace the existing runner providing a casting free of entrained air.

Abstract: The main aim of the metallurgical investigation was to enhance our understanding of the role Cu and Si have on the development of shrinkage porosity in the as-cast structure, which in turn can affect high cycle fatigue (HCF) properties of Al-9Si-1Cu (W328) and Al- 7Si-4Cu (W319) alloys. In order to achieve this objective a novel approach using thermal analysis and calculated fraction solid techniques was developed to assess mushy zone kinetics, the state between the liquidus and solidus where a solid skeletal α-Al phase and the Al-Si eutectic phase grow at the expense of an inter-dendritic liquid. Specifically, the cooling curve and calculated fraction solid curve were partitioned into segments, which reflect different stages of feeding through the entire solidification event of the alloy. Each partitioned segment corresponds to a stage of feeding, which in turn signifies a relative degree of pore growth susceptibility. Two thermal analysis techniques, both using calibrated thermocouples, were used to precisely understand the solidification path for both the W319 alloy and the W328 alloy.

Abstract: Computer based classification methodology is presented in the paper for defects being developed in the Al alloys as the car engine elements are made from them produced with the vacuum casting method. Identification of defects was carried out using data acquired from digital images obtained using the X-ray defect detection methods. The developed methodology as well as the related X-ray image analysis and quality control neural networks based software were carried out to solve this problem.

Abstract: The latent heat of solidification of any alloy depends on its chemistry that consequently affects the macro and microstructures for the given solidification conditions. In order to analyze the effects of chemistry on the release of latent heat during solidification of the industrial 3XX series of aluminum alloys, four different levels of silicon (5, 7, 9 and 11wt% Si) and three different levels of copper (1, 2 and 4 wt% of Cu) were taken into consideration. The solidification process was studied at cooling rates of 6 and 10°C/minute. The solidification path of these alloys was determined and the corresponding latent heat released during the solidification process was measured using a Differential Scanning Calorimeter (DSC). The tested hypoeutectic alloy chemical composition was expressed by the novel concept of silicon equivalency. The findings indicate that increases in the cooling rates shift the characteristic temperatures toward lower values without having a significant effect on the amount of released latent heat.

Abstract: The potential use of an Al-9Si-1Cu alloy (W328 alloy) as a replacement for W319 alloy in engine blocks was investigated.. The ambient mechanical properties (tensile, hardness and fatigue) of sand and permanent mould cast test bars along with bars machined from a sand cast automotive component were studied. The tensile properties were evaluated in as-cast and T6 heat-treated conditions. The effects of Fe and Mn on properties were also investigated. The castings in W328 alloy exhibit lower porosity than W319 alloy, which is attributed to the smaller solidification range and feeding distance and larger volume fraction of the eutectic phase. Higher iron levels increased the level of intermetallics and reduced properties. The addition of Mn did not offset the effect of higher iron levels. The W328 alloy offers some advantages over the 319 alloy and is a potential candidate for production of automotive components such as engine blocks and cylinder heads.

Abstract: In this work effect of cooling rate on the size of the grains, SDAS, β phases and thermal characteristic results of Al-Si cast alloys have been described. The solidification process was studied using the cooling and crystallization curve at cooling rate ranging from 0,1 °Cs-1 up to 1 °Cs-1. The main observation made from this work was that when cooling rate is increased the aluminum dendrites nucleation temperature and solid fraction at the dendrite coherency point increases, which implies that mass feeding is extended. In addition to that, it was observed that solidus temperature and size of the β phases decreases when cooling rate increases. Investigations were showed, that the thermal modification could be quantitatively assessed by analysis of the crystallization curve.