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

Abstract

The cooling curve analysis (CCA) has been used extensively in the metal casting industry, usually to predict alloy composition 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.Key words: Thermal Analysis, Al-Si alloys, Newtonian and Fourier methods. ABSTRAKTAnaliza krivih hladjenja je siroko primenjivana metoda u livnicama železnih i ne železnih metala/legura. U svakodnevnoj livačkoj praksi ova metoda je često korišćena za određivanje sastava legura i njihovih struktura. Primena ove metode može se znatno proširiti ukoliko bi se osnovna (nulta) linija ocvršćavanja legura matematicki tačno interpretirala. Newtonian i Fourier-ova metoda su opšte poznate metode za izračuna-vanje osnovnih/nultih linija krivih hlađenja. Obe metode su razvijene u cilju izračuna-vanja latentne toplote oslobođene tokom očvršćavanja čvrste faze različitih legura (u ovom radu su primenjene na leguri Al-7 wt.% Si). Uticaji promene gustine i toplotnog kapaciteta čvrste i tečne faze na izračunate vrednosti latentne toplote su analizirani u ovom radu. Izračunate vrednosti latentne toplote očvršćavanja su upoređene sa literaturnim podacima. U radu je takođe analiziran utical vrste tigla na eksperimentalno dobijene rezultate.Ključne reči: Termijska Analiza, Al-Si legure, Newtonian adn Fourier metode.

On the Newtonian Thermal Analysis of Casting: a Critical Aproach

“…Emadi et.al. reported that they used a crucible whose thermal mass was less than 0.5% of the total thermal mass of the system [7]. Yet, the thermal capacity of resin-coated sand molds used in this study were measured 117 J/K, while that of pure tin is 83 J/K.…”

A new baseline for the Newtonian thermal analysis of casting: two-capacitive system baseline

“…It is based on the measurement and analysis of the temperature of cooling sample in a small cup. CA-CCA techniques include the determination of liquidus and solidus temperature [5], grain refinement [6,7], phase transitions [4,8,9], dendrite coherency point [2,10], solid fraction, and latent heat [4,11,12]. Cooling curve analysis has been applied using various methods for several types of alloys in metallurgical applications [2][3][4][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

Cooling curve analysis in binary Al-Cu alloys: Part I- Effect of cooling rate and copper content on the eutectic formation

“…In recent years computer-aided cooling curve analysis (CA-CCA) has been used to determine thermo-physical properties of alloys, latent heat and solid fraction. Being very simple to setup it can be widely used, especially in industries [7][8][9][10][11]. The foremost use of cooling curves has been the determination of arrest points during solidification.…”