J. H. Sokolowski

On-line prediction of aluminum–silicon eutectic modification level using thermal analysis

Abstract Most contemporary evaluations of silicon modification level (ML) are done according to a specific scale based on an American Foundry Society (AFS) standard chart in aluminum–silicon casting. The structures depicted in the chart do not always resemble those seen in actual castings. Therefore, this procedure is subjective and can introduce bias into comparative metallographic analyses. Thermal analysis (TA) that incorporates image analysis algorithms can be a powerful on-line tool for estimating the degree of silicon modification in cast test samples. The aim of this work is to establish a methodology for the on-line quantitative control of aluminum–silicon ML using TA.

The removal of copper-phase segregation and the subsequent improvement in mechanical properties of cast 319 aluminium alloys by a two-stage solution heat treatment

Abstract The commercial heat treatment schedules that are utilized with cast AlSiCu alloys in order to obtain the optimum microstructure, and thereby optimum mechanical properties are often not effective because the precipitation strengthening process, which involves the precipitation of CuAl 2 or its precursors, does not occur in the desired manner since copper-rich phases, which form in the as-cast structure, are not fully dissolved in the aluminum solid solution during the solution treatment thus interfering with the desired precipitation on aging. Thermal analysis experiments for a 319 alloy show that the copper-rich phase in the as-cast alloy causes localized melting once the solution treatment temperature reaches 495°C, thus limiting single-stage (i.e., direct heating to temperature) solution treatment to temperatures of 495°C or below. To overcome these problems, a two-stage solution treatment has been developed for the 319 alloy where the conventional solution treatment is followed by a second solution treatment at a temperature above 495°C. Optical metallography showed that the two-stage solution treatment significantly reduces the amount of (as-cast) copper-rich phase in the alloy and gave rise to better homogenization prior to aging. Mechanical property measurements of cast alloys subjected to either the conventional or the two-stage solution treatments demonstrate the microstructural improvements generated by the two-stage process give rise to improve mechanical properties.

The Effect of the Melt Temperature and the Cooling Rate on the Microstructure of the Al-20% Si Alloy Used for Monolithic Engine Blocks

The Al-20%Si melt heated to 785°C (1445°F) and 850°C (1562°F) exhibited refinement of the primary Si while heating to 735°C (1355°F) produced coarse and heterogeneous primary Si crystals following the solidification process at approximately 1.3, 4.5, 15 and 35°C/s. The primary Si crystals were 40% finer for the samples heated to 850°C (1562°F) as compared with those heated to 735°C (1355°F). Higher cooling rates produced better primary Si refinement and minimized its variation caused by the melt temperature. The secondary dendrite arm spacing (SDAS) was not affected by the melt temperature and was a function of the cooling rate for the given experimental conditions. The SDAS changed from approximately 32 to 22μm for a 1.3 and 4.5°C/s cooling rate and was reduced to approximately 11μm for a 35°C/s cooling rate. Cooling curve analysis was used to analyze the sequence of the metallurgical transformations and fraction liquid development during alloy melting and solidification. The non-equilibrium thermal characteristics under cooling rate up to 15°C/s were analyzed as well. The experimental results were used to optimize the casting process and improve the service characteristics of the vacuum assisted high pressure die casting (HPDC) motorcycle engine blocks.

Thermoelectric power characterization of a 2024 aluminum alloy during solution treatment and aging

Abstract The solution treatment and aging of a 2024 aluminum alloy was studied using the thermoelectric power (TEP) measurement technique, and the results compared to those obtained by microhardness and optical microscopy. The TEP value changes with solution treatment temperature and duration and reaches a maximum value for solution treatment at 500 °C. The changes in TEP during solution treatment are caused by changes in the solubility of the alloying elements in α-Al. In the artificial aging process, the TEP value decreases with increasing aging time, but exhibits different characteristics for different stages of aging. In the initial stage, the TEP value decreases slowly and shows a fluctuating behavior for aging in temperatures below 190 °C. This fluctuation is caused by G.P. zone, G.P.B. zone, θ″, θ′, S″, and S′ formation which make different contributions to the TEP value. The TEP values corresponding to maximum microhardness for different aging temperatures are the same for a given solution treatment temperature. After the peak age, the TEP values decrease very quickly because the solubility of the alloying elements in α-Al decreases with aging time. The micro structural changes caused by precipitation during aging which cannot be observed by the light optical microscope were successfully monitored by the TEP measurement technique.

Methodology for Automatic Control of Automotive Al-Si Cast Components

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.

Comparison of Newtonian and Fourier thermal analysis techniques for calculation of latent heat and solid fraction of aluminum alloys

The cooling curve analysis (CCA) has been used extensively in the metal casting industry, usually to predict alloy compositio n and microstructure constituents. The use of CCA can be expanded to other areas of solidification if the zero curves can be properly calculated. In this paper the Newtonian and Fourier techniques of zero curve determination are described. These techniques were developed to calculate latent heat and to determine the correlations between solid fraction and temperature/time for Al-7 wt%Si alloy. The importance of the changes in heat capacity and density of solid and liquid phases during solidification on the latent heat calculations was examined. The latent heat calculated by Computer-Aided Cooling Curve Analysis (CA-CCA) method is compared with those reported in the literature. The effect of experimental procedure and type of sampling cup on the latent heat calculations were studied for both techniques.

Comparison Between Wedge Test Castings and Component Engine Block Casting Properties

A significant portion of the literature on new and/or modified alloy compositions that could serve as a replacement for the traditional 300 series aluminum alloys used for engine components are performed on test castings, which at times have limited complexity, lending themselves to advantageous liquid feeding conditions in the semi-solid state. More specifically the limited complexity of the test casting design may lead to conditions where progressive solidification provides enhanced soundness and limited segregation, which may not repeat in the component casting, made of the same alloy with the same melt treatment strategy.The research contained in this paper will investigate both a directionally chilled wedge test casting and a component engine block (CEB) poured with four development test alloys having the same melt treatment, with the aim to establish similarities and differences encountered in the test results of both casting designs used. The authors will make a recommendation regarding the best approach for successful alloy conversion strategies for production castings.

The Effect of Solidification Models on the Prediction Results of the Temperature Change of the Aluminum Cylinder Head Estimated by FDM Solidification Analysis

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.

The Effect of Chemistry and Cooling Rate on the Latent Heat Released during the Solidification of the 3XX Series of Aluminum Alloys

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.

Influence of Cooling Rate on the Size of the Precipitates and Thermal Characteristic of Al-Si Cast Alloys

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.